BRITISH STANDARD
BS 5628-3: 1985 (Reprinted, incorporating Amendment No. 1)
Code of practice for
Use of masonry — Part 3: Materials and components, design and workmanship — (formerly CP 121-1)
UDC 624.012:693.1/.3
BS 5628-3:1985
Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Civil Engineering and Building Structures Standards Committee (CSB/-) to Technical Committee CSB/33, upon which the following bodies were represented: Association of Consulting Engineers Autoclaved Aerated Concrete Products Association Brick Development Association British Ceramic Research Association British Precast Concrete Federation Ltd. Building Employers Confederation Calcium Silicate Brick Association Limited Cement and Concrete Association Department of the Environment (Building Research Establishment) Department of the Environment (Housing and Construction Industries) Department of the Environment (Property Services Agency) District Surveyors Association Greater London Council Incorporated Association of Architects and Surveyors Institution of Civil Engineers Institution of Structural Engineers
The following bodies were also represented in the drafting of the standard, through sub-committees and panels: Aggregate Concrete Block Association Association of British Roofing Felt Manufacturers Association of Teachers in Technical Institutions Eurisol (UK) Association of Manufacturers of Mineral Fibre Insulation Fire Offices Committee Institute of Clerks of Works of Great Britain Inc. National Cavity Insulation Association National Federation of Clay Industries Ltd. Refractories Association of Great Britain Royal Institute of British Architects Royal Institution of Chartered Surveyors Coopted members
This British Standard, having been prepared under the direction of the Civil Engineering and Building Structures Standards Committee, was published under the authority of the Board of BSI and comes into effect on 29 March 1985 © BSI 11-1999 The following BSI references relate to the work on this standard: Committee reference CSB/33 Draft for comment 77/11249 DC ISBN 0 580 14368 6
Amendments issued since publication Amd. No.
Date of issue
Comments
4974
November 1985
Indicated by a sideline in the margin
BS 5628-3:1985
Contents Page Committees responsible Inside front cover Foreword iii Section 1. General 1 Scope 1 2 Definitions 1 3 Related British Standards 3 4 Alternative materials, components and methods of design and construction 3 Section 2. Materials and components 5 Masonry units 4 6 Materials for mortar 4 7 Wall ties 4 8 Anchorages, dowels and fixings 4 9 Reinforcement 6 10 Damp-proof courses 6 11 Sealants 6 12 Airbricks, gratings and flues 6 13 Sills 6 14 Lintels 7 15 Copings 7 16 Flashings and weatherings 8 Section 3. Design 17 General 9 18 Design for stability 10 19 Structural detailing for stability 19 20 Movement in masonry 31 21 Exclusion of moisture 36 22 Durability 56 23 Selection of mortars 67 24 Fire resistance 68 25 Thermal properties 73 26 Sound absorption and noise reduction 73 27 Masonry bonds and other constructional details 74 Section 4. Workmanship 28 Setting out 83 29 Scaffolding 83 30 Storage on site 83 31 Batching, mixing and use of mortars 84 32 Laying of masonry units 86 33 Constructional details 90 34 Provision of services, including fixings and chases 91 35 Protection against damage during construction 91 36 Supervision 92 Appendix A Determination of movement in masonry 93 Appendix B Masonry bonds and joint finishes 98 Index 102 Figure 1 — Wind zones 12 Figure 2 — Walls with edge restraint 14
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Page Figure 3 — Fixed support conditions in solid walls 15 Figure 4 — Fixed support conditions in cavity walls 16 Figure 5 — Fixed and simple supports 17 Figure 6 — Limiting dimensions of internal walls for stability 18 Figure 7 — Typical ways of connecting floors and roofs 20 Figure 8 — Typical anchorages, dowels and fixings 26 Figure 9 — Typical chimney details 29 Figure 10 — Movement joints 35 Figure 11 — Overlap between exposure categories 38 Figure 12 — Damp-proof systems 47 Figure 13 — Matching facing masonry 77 Figure 14 — Brick arches 81 Figure 15 — Sizes of corbels 82 Figure 16 — Factors affecting movement 96 Figure 17 — Brick masonry bonds 99 Figure 18 — Block masonry bonds 100 Figure 19 — Joint finishes 101 Table 1 — Anchorages, dowels and fixings 5 Table 2 — Sills 6 Table 3 — Lintels 7 Table 4 — Copings 7 Table 5 — Flashings and weatherings 8 Table 6 — Selection of materials for masonry 10 Table 7 — Height to thickness ratio for freestanding single-leaf walls without piers 11 Table 8 — Maximum permitted areas of certain walls 13 Table 9 — Wall ties 28 Table 10 — Classification of exposure to local wind-driven rain 37 Table 11 — Assessment of resistance to rain penetration 39 Table 12 — Physical properties and performance of materials for d.p.cs 42 Table 13 — Durability of masonry in finished construction 59 Table 14 — Protection of metal components (other than wall ties) built into masonry 66 Table 15 — Mortar mixes 67 Table 16 — Notional fire resistance of walls 69 Table 17 — Ready-mixed lime : sand mixes for specified cement : lime : sand mortars 85 Table 18 — Bulk density, water demand and yield of wet mortars 86 Table 19 — Linear thermal movement of masonry units and mortar 94 Table 20 — Moisture movement of concrete and calcium silicate masonry units 95 Table 21 — Shrinkage of mortars due to change in moisture content 95 Publications referred to Inside back cover
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BS 5628-3:1985
Foreword This Part of BS 5628, prepared under the direction of the Civil Engineering and Building Structures Standards Committee, is a new code of practice for the design and construction of brick and block masonry. It supersedes CP 121-1:1973, which is therefore withdrawn. The recommendations of this code are based on experience of single-leaf and unfilled cavity walls. Filling the complete cavity of a wall with thermal insulation will increase the risk of rain penetration through the wall. (See BRE Digest 236 “Cavity Insulation” 19801).) Accordingly, a number of recommendations have been made for design detailing and workmanship to minimize this effect of cavity insulation on the performance of the wall. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations.
Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 108, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. 1) Available
© BSI 11-1999
from the Building Research Station, Garston, Watford, Herts WD2 7JR.
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BS 5628-3:1985
Section 1. General 1 Scope This Part of BS 5628 gives general recommendations for the design and construction of brick and block masonry, including materials and components, the main aspects of design, other than structural, which is covered by BS 5628-1 and BS 5628-2, and workmanship. This code does not cover natural stone masonry. Reference should be made to BS 5390. NOTE The publications referred to in this standard are listed on page 107.
2 Definitions
2.7 datum defined level to which other levels may be related 2.8 efflorescence salts on the surface of the wall left by evaporation (see clause 22) 2.9 fair faced work built with particular care, both to line and with even joints, where the finished work is to be visible
For the purposes of this standard the definitions given in BS 6100-5 or in the British Standard for the given material or component apply together with the following.
2.10 frog
2.1 bat
2.11 indenting
portion of a brick either specially manufactured or cut on site 2.2 capping unit or assemblage placed at the head of a wall that does not shed rainwater from the top of the wall clear of all exposed surfaces of the walling beneath NOTE Examples of cappings are brick-on-edge and other cappings that may be flush or overhanging but that do not incorporate a throating or other device designed to shed rainwater clear of the walling beneath.
2.3 cavity tray
purpose-made indentation in either or both of the bed faces of a brick
recesses formed in masonry to receive future work 2.12 jamb part of a wall at the side of an opening 2.13 jointing finishing of a mortar joint as the work proceeds (see B.3) 2.14 lime bloom particular kind of efflorescence (see 2.8)
component provided to divert water that has entered a cavity to the outside of the building
2.15 masonry
2.4 closer
assemblage of units jointed with mortar
portion of a masonry unit used to maintain masonry bond, either specially manufactured or cut [see Figure 17(a)] 2.5 coping unit or assemblage placed at the head of a wall and designed to shed rainwater from the top of the wall clear of all exposed faces of the walling it is intended to protect NOTE Examples of copings are copings complying with BS 5642-2, some types of continuous sheet metal or extruded plastic copings and built up details, such as tile creasing.
2.6 course layer of masonry that includes a layer of mortar as well as a layer of units
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2.16 masonry bond disposition of units in masonry (for examples, see B.1 and B.2) 2.17 masonry unit brick or block 2.18 panel area of masonry with defined boundaries, that may contain openings 2.19 pier member that forms an integral part of a wall, in the form of thickened sections placed at intervals along the wall
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2.20 pointing
2.26.2 header
filling and finishing of raked-out joints
masonry unit laid on its bed face with its longer face perpendicular to the face of the wall [see Figure 17(a)]
2.21 quoin external corner 2.22 string course distinctive course in a wall, usually horizontal, and projecting 2.23 toothing
2.26.3 pistol brick brick, purpose made or sawn from whole brick on site to form an accurate sized rebated shape to fit over and face the nibs [see Figure 13(b)] 2.26.4 slip
2.24 Types of joint
masonry unit, either specially manufactured or cut, of the same height and length as a header (see 2.26.2) or stretcher (see 2.26.8), and usually with a thickness of between 20 mm and 50 mm
2.24.1 bed joint
2.26.5 snap header
mortar layer upon which masonry units are set
half unit with its end showing as a header (see 2.26.2) on the face of the wall
masonry units left projecting to bond with future work
2.24.2 collar joint continuous vertical joint parallel to the face of the wall 2.24.3 cross joint joint, other than a bed joint, at right angles to the face of a wall
2.26.6 special unit masonry unit whose shape is other than a rectangular prism 2.26.7 squint special brick used at an oblique quoin
2.24.4 movement joint (control joint)
2.26.8 stretcher
joint designed to permit relative movement of sections of a structure built in masonry to occur without impairing the functional integrity of the structure (see Figure 10)
masonry unit laid on its bed with its longer face parallel to the face of the wall [see Figure 17(a)]
2.24.5 perpend joint vertical cross joint 2.25 shell bedding bedding consisting of two separate strips of mortar covering the outer and inner face shells of the blocks in both horizontal and vertical joints, neither strip being more than 50 mm wide
2.27 Types of support 2.27.1 fixed support support to the edge of a wall that restrains the wall against lateral movement and also substantially against rotation [see Figure 5(a)] 2.27.2 simple support support to the edge of a wall that may permit rotation but restrains the wall against lateral movement [see Figure 5(b)]
2.26 Types of masonry unit
2.28 Types of wall
2.26.1 fixing unit
2.28.1 single-leaf wall
masonry unit made to facilitate the driving of nails and screws and to achieve good holding
wall of masonry units laid to overlap in one or more directions and set solidly in mortar
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BS 5628-3:1985
2.28.2 cavity wall two parallel single-leaf walls, usually at least 50 mm apart and effectively tied together with wall ties 2.28.3 double-leaf (collar-jointed) wall two parallel single-leaf walls, with a space between not exceeding 25 mm, filled solidly with mortar and so tied together as to result in common action under load 2.28.4 freestanding wall wall without top or side support that depends for stability on its mass and/or base fixity 2.28.5 grouted cavity wall two parallel single-leaf walls, spaced at least 50 mm apart, effectively tied together with wall ties and with the intervening cavity filled with fine aggregate concrete (grout) that may be reinforced so as to result in common action under load 2.28.6 sleeper wall wall, usually honeycombed, built to support a suspended ground floor 2.28.7 veneered wall wall having a facing that is attached to the backing, but not so bonded as to result in common action under load 2.29 weathering cover applied to a structure, or the geometrical form of a part of a structure, enabling rain-water to be shed
© BSI 11-1999
3 Related British Standards This code gives general guidance applicable to all brick and block masonry. In certain cases its recommendations may need to be supplemented by reference to other British Standards, including the following. Analysis of structures Unreinforced masonry
BS 5628-1
Reinforced and prestressed masonry
BS 5628-2
Accuracy in building
BS 5606
Access for the disabled to buildings
BS 5810
Basic data for design of buildings
BS 6399, CP 3
Cleaning and surface repair of masonry
BS 6270-1
Foundations
CP 101, CP 2004
Manholes
BS 8301, CP 2005
4 Alternative materials, components and methods of design and construction Where materials, components and methods of design and construction are not covered by this code or by any other British Standard, this is not to be regarded as discouraging their use. The designer should satisfy himself by reference to appropriate manufacturers’ literature and test certificates issued by competent, independent authorities that the materials and methods to be employed are such as to ensure a level of performance at least equal to that recommended in this standard.
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Section 2. Materials and components 5 Masonry units
6.5 Water
5.1 Fired-clay masonry units
Water should be mains water or other potable supply. If mains water is not available, the water should be clean and should not contain any material, either in solution or in suspension, in quantity sufficient to have a harmful effect on the mortar or on metals or to impair the durability of the construction. In cases where water supplies may be of doubtful quality, the methods of sampling and testing the water should be as described in BS 3148.
Fired-clay masonry units should comply with BS 3921 or BS 6649. 5.2 Calcium silicate masonry units Calcium silicate masonry units should comply with BS 187 or BS 6649. 5.3 Concrete masonry units Concrete masonry units should comply with the relevant British Standard. Concrete flue blocks
BS 1289
Precast concrete masonry units
BS 6073-1
Reconstructed stone masonry units
BS 6457
6 Materials for mortar 6.1 Cement Cement should comply with the relevant British Standard. Portland cement (ordinary and rapid hardening)
BS 12
Portland blastfurnace cement
BS 146-2
Sulphate-resisting Portland cement
BS 4027
Masonry cement
BS 5224
6.2 Lime Limes should comply with BS 890. 6.3 Aggregate 6.3.1 Natural aggregates. When specifying aggregates from natural sources designers should refer to BS 882 or BS 1200. For guidance, see clause 23. 6.3.2 Lightweight aggregates. Lightweight aggregates should comply with BS 877-2 or BS 3797-2. 6.4 Admixtures 6.4.1 General. Admixtures may affect the strength and adhesion of mortars and care should be exercised in their use. For guidance, see clause 23. 6.4.2 Calcium chloride. Calcium chloride and admixtures containing calcium chloride should never be added to mortars (see 23.3). 6.4.3 Plasticizers. Mortar plasticizers should comply with BS 4887. For guidance on use, see 23.2.5 and 31.3. 6.4.4 Colouring agents. Colouring agents (pigments) should comply with BS 1014. For guidance on use, see 31.3.
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6.6 Ready-to-use mortars and ready-mixed lime : sand Ready-mixed lime : sand for mortar and ready-to-use retarded cement : lime : sand and retarded cement : sand mortars, which are all delivered wet to the site, should comply with BS 4721. Dry-packaged cementitious mixes should comply with BS 5838-2. NOTE 1 The term sand is used here to include all permitted aggregates. NOTE 2 Ready-mixed lime : sand for mortar is produced by adding damp sand to lime in the form of lime putty or dry hydrated lime. This process is normally undertaken in a factory away from the building site. NOTE 3 Ready-to-use building mortars are factory made mortars (cement : lime : sand and cement : sand) which contain a cement-set retarding admixture and require no further treatment before use. The cement is normally ordinary Portland cement but may be sulphate-resisting Portland cement or Portland-blastfurnace cement or, for non-lime mortars, masonry cement.
7 Wall ties Wall ties should comply with BS 1243. For guidance on selection and use of wall ties, see 19.5.
8 Anchorages, dowels and fixings Materials for anchorages, dowels and fixings, including bonding ties, joist hangers and lateral restraint straps, are given in Table 1. For guidance on selection of materials for anchorages, dowels and fixings, see 22.7.1. Typical fixings are illustrated in Figure 8. Joist hangers required only for vertical support should comply with BS 6178-1. Joist hangers required both for vertical support and lateral support, as shown in Appendix C of BS 5628-1:1978, should be purpose made.
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BS 5628-3:1985
Table 1 — Anchorages, dowels and fixings Category
A
Base material
Hot-dip galvanized low carbon steel
Form
Grade and standard to be complied with
Sheet BS 2989, Z1 or Z2, coating type G 600. Minimum mass of coating 600 g/m2 including both sides
BS 2989, Z1 or Z2, coating type G 275. Minimum mass of coating 275 g/m2 including both sides
B
Low carbon steel Strip BS 1449-1:1983 (mechanical requirements in Table 11 only) BS 4360 grade 43A
C
Low carbon steel Strip BS 1449-1:1983 (mechanical requirements in Table 11 only) BS 4360 grade 43A
D
Copper Copper alloys
BS 6017 BS 2870:1980, grades listed in Tables 8 and 12 BS 2873:1969, grades listed in Tables 4 and 6 BS 2874:1968, grades listed in Tables 6, 8 and 9 except CA 106
Austenitic stainless steel, minimum 18/8 composition and excluding free machining specifications
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Strip Bar Rod Tube Wire
Protective measures to be carried out after fabrication
All external cut edges to be protected using a one-pack chemical-resistant paint complying with HF1A to HF2F in part 4 of Table 4H of BS 5493:1977 and modified to give adequate adhesion to the fixing Coating to be applied after fabrication to the external surfaces and consisting of either: a) bituminous solution complying with types 1 or 2 of BS 3416 and of minimum thickness 25 4m; or b) a one-pack chemical-resistant paint complying with HF1A to HF2F in part 4 of Table 4H of BS 5493:1977 and modified to give adequate adhesion to the fixing. Where the zinc is removed on internal surfaces during fabrication, e.g. by welding, further protection should be applied to these areas Post-galvanizing complying with BS 729. Minimum mass of coating 460 g/m2 including both sides Post-galvanizing complying with BS 729. Minimum mass of coating 940 g/m2 including both sides Material other than phosphor bronze to be formed either: a) by bending at dull red heat and allowing to cool in still air; or b) by cold forming and subsequently stress relief annealing at 250 °C to 300 °C for 30 min to 1 h Effectiveness of stress relieving of cold formed components to be tested by the supplier using the mercurous nitrate test described in clause 11 of BS 2875:1969
BS 1449-2 BS 970-1 BS 6323-8 BS 1554 BS 3111-2
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9 Reinforcement
11 Sealants
Reinforcement for structural use should follow the recommendations of BS 5628-2. Reinforcement for non-structural use, e.g. crack control (see 20.5), should be of a type approved by the designer. Stainless steel reinforcement should be fabricated from austenitic stainless steel complying with grades 3042S15, 316S31 or 316S33 of BS 970-1. Other types of steel reinforcement should be protected against corrosion (see 22.7).
Sealants should comply with the relevant British Standard.
10 Damp-proof courses
12 Airbricks, gratings and flues
Materials for damp-proof courses (d.p.cs) should comply with the relevant British Standard.
Airbricks and gratings should comply with BS 493. Flues should follow the recommendations of BS 5440-1 or BS 6461, as appropriate.
One-part polysulphide sealants
BS 5215
Two-part polysulphide sealants
BS 4254
Silicone-based building sealants
BS 5889
For guidance on choice and application of sealants and back up materials, see 20.4.
Bitumen
BS 6398
Brick
BS 3921
13 Sills
Polyethylene
BS 6515
All others
BS 743
Sills should comply with the relevant British Standard given in Table 2. For guidance on d.p.cs below sills, see 21.5.3.
The criteria for suitability of materials for d.p.cs are set out in 21.4 and Table 12. Table 2 — Sills Material
Standard to be complied with
Brick and block
BS 187, BS 3921 or BS 6073-1
Cast stone
BS 5642-1
Clay tile
BS 402
Clayware
BS 5642-1
Concrete
BS 5642-1
Natural stone
BS 5642-1
Slate
BS 5642-1
Steel
BS 6510
Timber
BS 1186-1 and BS 1186-2 and BS 5642-1
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Other recommendations
Sills formed from bricks or blocks should be in accordance with Table 13 (I)
Timber sills should comply with the requirements for coordinating dimensions and performance given in BS 5642-1 and the requirements for quality given in BS 1186-1 and BS 1186-2
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BS 5628-3:1985
14 Lintels
15 Copings
Lintels should comply with the relevant British Standard given in Table 3. For guidance on use, see 19.3 and on workmanship, see 33.4.
Copings should comply with the relevant British Standard given in Table 4. For guidance on use, see 21.6. Copper copings may cause staining of external walls. To avoid electrolytic action between metallic copings and metal roofing where dissimilar metals are to be used, consideration should be given to the use of non-metallic copings. Table 3 — Lintels
Material
Standard to be complied with
Autoclaved aerated concrete Cast concrete Reinforced concrete
BS 5977-2
Pressed steel Rolled low carbon steel
BS 5977-2
Prestressed concrete plank
BS 5977-2
Reinforced masonry
BS 5628-2
Timber
BS 5977-2
Other recommendations
Bricks and blocks used for lintels should be of the appropriate quality recommended in Table 13.
Table 4 — Copings Material
Standard to be complied with
Recommended thickness
Other recommendations
mm
Aluminium
BS 1470
0.9 min.
Brick and block BS 187, BS 3921 or BS 6073-1 Cast stone
BS 5642-2
Clay tile
BS 402 or BS 1286
Commercial or super purity quality aluminium should be used. Copings should preferably be preformed Copings formed from bricks or blocks should be of the appropriate quality recommended in Table 13 (I)
Concrete (cast ) BS 5642-2 Concrete tile
BS 473 & BS 550 or BS 1197
Copper
BS 2870, grades C 104 or C 106 in the O condition
Lead
BS 1178
Natural stone
BS 5642-2
Zinc
BS 849
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1.8 min. (code no. 4) 0.8 min.
Copings should preferably be preformed. In heavily polluted atmospheres, it is advisable to use a heavier sheet, e.g. 1.0 mm thick or use another material
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16 Flashings and weatherings Flashings and weatherings should comply with the relevant British Standard given in Table 5. For guidance on use, see 21.6. Table 5 — Flashings and weatherings Material
Standard to be complied with
Recommended thickness
Other recommendations
mm
Aluminium BS 1470 Aluminium alloy
0.6 to 0.9 (sheet or strip)
See CP 143-16
Asbestos bitumen sheet (semi-rigid) Bituminous felt
BS 747
Copper
BS 2870 grades C 104 and C 106 in the O condition
0.4 to 0.7
Lead
BS 1178
1.8 min. (code no. 4)
Zinc
BS 849
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Flashings and weatherings should be protected from contact with mortar by a coating of bituminous paint
For guidance on installation, see CP 144
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BS 5628-3:1985
Section 3. Design 17 General
17.5 Adhesion
17.1 Factors to be considered
It is essential to ensure that in any masonry construction adequate adhesion exists between the masonry units and the mortar. Where the design relies on flexural strength and there is insufficient experience or information on the adhesion characteristics of particular masonry units and mortar designations, preliminary tests as described in A.3 of BS 5628-1:1978 should be carried out to establish whether adequate adhesion can be achieved. Depending on their characteristics, masonry units may be highly porous and, particularly in warm weather, rapidly absorb the moisture from the mortar when laid. In such cases the mortar becomes harsh and insufficiently plastic to allow repositioning of the unit during laying and levelling and it is possible that no adhesion between the unit and the mortar will be obtained. Experience has shown that adhesion will be adversely affected when masonry is allowed to dry out rapidly in warm, dry conditions. Laying mortar beds in shorter lengths, thus limiting water loss from the mortar before the next course is laid, is advantageous in such conditions. Wetting may assist in removing dust from bricks and thus further improve adhesion. However, the bricks should not be over wetted, as this may lead to “floating” on the mortar bed and also to excessive efflorescence and staining of the brick face. In fired-clay brickwork, optimum adhesion is likely to be achieved when the suction rate of the bricks at the time of laying is not greater than 1.5 kg/(m2.min). A suitable test for suction rate of fired-clay bricks is given in Appendix H of BS 3921:1985. Where the achievement of maximum flexural strength is critical, e.g. in infill panels, and bricks of higher suction rate are used, the consistency of the mortar should be adjusted or the bricks should be wetted (docked) just before use. In very dry conditions, easier laying and better adhesion of calcium silicate bricks may be achieved by adjusting the consistency of the mortar or dipping the bricks briefly in water just before use. The bricks should not be soaked in water. Concrete masonry units should not be wetted. Instead, the consistency of the mortar should be adjusted to suit the suction, if necessary using water-retaining admixtures. For guidance on the characteristics of particular masonry units and appropriate wetting procedures, the manufacturer should be consulted.
The designer should consider the following factors when designing masonry: a) stability (see clauses 18 and 19); b) accommodation for movement (see clause 20); c) adhesion (see 17.5); d) resistance to rain penetration (see clause 21); e) durability (see clause 22); f) fire, thermal and acoustic performance (see clauses 24, 25 and 26); g) masonry bonds, provision of services and other constructional details (see clause 27). Other factors, not dealt with in detail in this code, may also need to be considered: 1) whether there is an applied facing or finish to provide characteristics not inherent in the basic construction, and the compatibility of this facing or finish with the masonry; 2) the effect of the weight of the wall, including finishes, on the strength of the supporting structure; 3) the effect of the thickness of the wall, including finishes, on the useable floor area; 4) speed of construction; 5) accuracy of construction. 17.2 Loading The loading requirements for masonry and the lateral wind pressures that should be allowed for in design are given in BS 6399-1 and CP 3:Chapter V-2. Masonry should also be designed to withstand any additional loads which may arise, e.g. if materials are to be stacked or heaped against walls. 17.3 Impact resistance Impact damage may be caused to walls in various ways. Where there is an applied finish, resistance to light impacts is largely a matter of the resistance of this finish. Where the wall is likely to be subject to heavier impact loads, either the structure of the wall and the applied finish should be sufficiently strong and stable to withstand the impact without undue damage, or the wall should be protected, e.g. by positioning of bollards where there is danger of damage from motor vehicles. 17.4 Foundations Masonry walls should be built on adequate foundations. For guidance, see CP 101 and CP 2004.
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17.6 Selection of masonry units and materials
18.3 Walls subjected to concentrated loads
The selection of masonry units and associated materials should be made bearing in mind the criteria listed in Table 6. Table 6 — Selection of materials for masonry
Where a concentrated load occurs in a wall, e.g. at a lintel or beam bearing, due regard should be given to the local bearing stress (see clause 34 of BS 5628-1:1978) and, where necessary, suitable bearing plates, spreader beams, padstones, piers or columns should be provided. Lintels or beams should not bear on a short length of cut block. Where possible, the masonry should be set out to provide a full block under a bearing. Certain types of cellular, frogged or hollow unit which are normally suitable for the construction of the wall may not provide sufficient bearing strength at points of concentrated load and may need to be filled.
Criterion
Clause reference
Durability
22
Strength
18, 23
Adhesion
17.5
Fire resistance
24
Thermal and acoustic properties
25, 26
Handling, including weight of blocks
35
Appearance
—
18 Design for stability 18.1 Masonry in general All masonry should be designed to have adequate strength, stiffness and stability. The designer should consider the interaction of the whole structure, of which the masonry forms part, to ensure that connections of other elements with walls are sufficient to transmit all vertical and lateral loads safely to the foundations. Temporary support for masonry during construction may need to be considered, e.g. where composite action is required. Recommendations for the structural design of masonry are given in BS 5628-1 and BS 5628-2. Depending on the type of masonry, the necessary stiffness and stability are derived from one or more of the following. a) Thickness in relation to height and length. NOTE The useful thickness will be reduced by using recessed joints.
b) Self weight. c) Presence of piers. d) Interaction with other walls, columns, floors, roofs or structural elements. Careful consideration should be given to the effect of introducing movement joints or slip planes. The designer should always bear in mind the need for robust construction, including the effect of accidental loading. 18.2 Walls and columns subjected to imposed vertical and lateral loads Walls and columns subjected to imposed vertical and lateral loads should be designed following the recommendations of BS 5628-1 or BS 5628-2.
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18.4 Walls subjected to imposed lateral load only 18.4.1 Freestanding walls. The recommendations in this subclause apply to freestanding single-leaf walls without piers that are subjected only to wind loads. Other types of freestanding wall should be designed following the recommendations of BS 5628-1 or BS 5628-2. For guidance on loading and minimum heights for parapets and balustrades, see BS 6180. Freestanding single-leaf walls without piers that are subjected only to wind loads may be designed with a height to thickness ratio as given in Table 7, subject to the following conditions. a) The height should be taken to be the overall height of the wall above the level of lateral restraint. b) The walls should be constructed of masonry units having a compressive strength not less than 3.5 N/mm2 and a density not less than 1 400 kg/m3, subject to the recommendations for durability given in clause 22. c) The walls should be located in an area with many windbreaks, such as a town, city or well wooded area, i.e. in protection category 3 described in DD 93. If the wall is located in open farmland, on the top of an escarpment or cliff, or in any other exposed area, the wall should be designed following the recommendations of BS 5628-1 or BS 5628-2. d) The walls should either not contain a horizontal d.p.c. or have a d.p.c. which is capable of developing the same flexural resistance as the remainder of the wall, e.g. engineering bricks.
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Table 7 — Height to thickness ratio for freestanding single-leaf walls without piers Wind zone (see Figure 1)
Maximum permitted height to thickness ratio, R
8.5 7.5 6.5 6.0
1 2 3 4
A horizontal d.p.c. which cannot resist flexure will reduce the stability of the wall. If such a d.p.c. is used, the wall thickness should be taken to be the greater of: 1.33hd/R, or hl/R, where hd is the height of the wall above the d.p.c.; R is the ratio obtained from Table 7 for the appropriate wind zone; hl is the height of the wall above the lowest level of lateral restraint below the d.p.c.; lateral restraint to the base of walls may be assumed where there is a continuous support, .e.g. a concrete slab. 18.4.2 Walls with edge restraint 18.4.2.1 Maximum areas of walls. Walls with edge restraint which are subjected to wind loads may be designed following the recommendations of BS 5628-1. However, certain rectangular walls and gables in buildings up to and including four storeys high may be proportioned as given in Table 8, subject to the following conditions. a) The walls should be in buildings up to and including four storeys high situated in the wind zones shown in Figure 1. b) The building of which the wall forms part should be situated in an area with many windbreaks, such as a town, city or well wooded area, i.e. in protection category 3 described in DD 93. If the building is located in open farmland, on the top of an escarpment or cliff, or in any other exposed area, the wind pressure should be obtained from CP 3:Ch V-2 and the wall designed following the recommendations of BS 5628-1 or BS 5628-2. c) The walls should be free from any doors, windows or other openings, unless either: 1) intermediate supports are provided, such as those shown in Figure 2(a); or
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2) the total area of such openings is not greater than 10 % of the appropriate maximum area given in Table 8 or 25 % of the actual area of the wall, whichever is the less, and no opening is less than half its maximum dimension from the edge of the wall, other than its base, or from any other opening [see Figure 2(b)]. d) In a single-leaf, double-leaf or grouted-cavity wall, the distance between supports should not exceed 40 times the total thickness of the wall. e) In a cavity wall: 1) the distance between supports should not exceed 30 times the total thickness of the masonry in the wall; 2) the thickness of each leaf should be not less than 100 mm excluding plaster or render; 3) the cavity width should not exceed 100 mm; 4) wall ties should be spaced in accordance with 19.5. f) Pitched gable ends which have support at the top (see 19.2) should be regarded as being equivalent to a rectangular area whose height is measured to half way up the triangular portion [see Figure 2(c)]. Three-or four-sided support should be assumed as appropriate. g) Mortar should not be weaker than designation iii) (see Table 15). 18.4.2.2 Support conditions. A fixed support may be assumed in a single-leaf, double-leaf or grouted-cavity wall in the cases shown in Figure 3 or where the wall abuts, and is adequately tied to, a column capable of resisting without excessive deflection horizontal forces applied to it. A fixed support may be assumed in a cavity wall in the cases shown in Figure 4. A simple support may be assumed where the wall is permitted to rotate but is restrained against lateral movement. In all cases, the wall should be adequately connected to its support and all supports should be sufficiently strong and rigid to carry the transmitted loads. For guidance, see Figure 5. Any chases cut in the wall should be taken account of (see 19.6).
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Figure 1 — Wind zones (for use with 18.4)
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Table 8 — Maximum permitted areas of certain walls Wind Height zone
A
B
C
D
E
F
G
H
I
Cavity 190 mm Cavity 190 mm Cavity 190 mm Cavity 190 mm Cavity 190 mm Cavity 190 mm Cavity 190 mm Cavity 190 mm Cavity 190 mm solid solid solid solid solid solid solid solid solid wall wall wall wall wall wall wall wall wall wall wall wall wall wall wall wall wall wall
1 2 3 4
m
m2
m2
m2
m2
m2
m2
m2
m2
m2
m2
m2
m2
5.4
11.0
13.5
17.5
19.0
26.5
28.5
20.5
29.0
32.0
41.0
32.0
41.0
10.8
9.0
11.5
13.0
15.5
17.5
21.5
15.5
23.5
24.0
32.5
32.0
5.4
9.5
12.0
14.0
17.0
21.0
24.0
17.5
25.5
27.0
35.5
10.8
8.0
9.5
11.5
14.0
13.5
17.5
13.0
20.5
19.0
5.4
8.5
10.5
12.5
15.0
15.5
20.0
14.5
22.5
10.8
7.0
8.5
10.0
12.0
11.5
15.5
11.0
5.4
8.0
9.5
11.0
13.5
13.0
17.0
10.8
6.5
7.5
9.0
11.0
10.5
13.5
m2
m2
m2
m2
m2
m2
8.5
10.0
14.0
19.0
19.5
30.5
41.0
7.0
8.0
10.0
14.5
15.5
21.5
32.0
41.0
7.5
8.5
10.5
16.5
17.0
24.5
28.5
28.0
36.5
6.0
7.0
9.0
11.0
13.0
17.5
22.0
31.0
30.5
40.5
6.5
7.5
9.5
13.5
14.5
20.0
17.5
14.5
24.5
24.5
31.5
5.0
6.0
7.5
9.0
11.5
15.0
12.5
19.5
18.0
27.5
27.0
35.0
6.0
6.5
8.5
10.5
12.5
17.0
9.5
14.5
12.5
21.0
21.5
27.5
4.0
5.5
6.5
7.5
10.0
12.5
NOTE 1 Key to support conditions. Types of support are described in 18.4.2.2. Free edge shown thus Simple support shown thus Fixed support shown thus NOTE 2 The term solid is used in this table to denote single-leaf walls, collar-jointed walls (see 2.28.3) or grouted-cavity walls (see 2.28.5). The 190 mm solid walls are of any brick, or blocks of compressive strength not less than 3.5 N/mm2. NOTE 3 Cavity walls consist of the following: a) an outer leaf, 100 mm minimum thickness, of any brick or blocks of compressive strength not less than 14.0 N/mm2. b) an inner, leaf, 100 mm minimum thickness, of any brick, or blocks of compressive strength not less than 3.5 N/mm2. If either leaf of a cavity wall is increased to 140 mm using blocks of the respective strength, the areas given in the table may be increased by 20 %.
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(a) Example of division of a wall into panels with intermediate supports
is the maximum dimension of opening (height or length) A0 is the permitted area of opening [see 18.4.2.1 c)]. (b) Effect of opening in a wall x
(c) Gable walls [see 18.4.2.1 f)]. Figure 2 — Walls with edge restraint
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Figure 3 — Fixed support conditions in solid walls
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Figure 4 — Fixed support conditions in cavity walls
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Figure 5 — Fixed and simple supports
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18.5 Internal walls or partitions not designed for imposed loading Unless it is designed as a freestanding wall (see 18.4.1), an internal wall or partition should be laterally restrained by horizontal or vertical continuous or intermittent supports, similar to those given in Table 8. The length or height of the wall in relation to its thickness should be within the limits given in Figure 6. Consideration should also be given to the following factors which may affect stability: a) accommodation for movement (see clause 20); b) openings; c) chasing (see 19.6); d) the likelihood of exceptional lateral loading, arising from the nature of use of the building; e) wind load (see CP 3:Ch V-2).
Where it is known that an internal wall or partition is to be plastered, a maximum thickness of 13 mm of plaster to one side or both sides of the partition may be included when determining the thickness of the wall for design in accordance with Figure 6. In such a case, the wall may require temporary bracing prior to plastering. NOTE The graphs in Figure 6 are derived from the following empirical formulae: i) wall restrained at both ends but not at the top t W L/40 and t W H/90 or t W H/15 with no restriction on the value of L or t < L/40 and t > L/59 and t W H + 2 L)/133; ii) wall restrained at both ends and at the top t W L/50 and t W H/90 or t W H/30 with no restriction on the value of L or t < L/40 and t W L/110 and t W (3H + L)/200; iii) wall restrained at the top but not at the ends t W H/30; where t is the thickness (in mm); H
is the height (in mm);
L
is the length (in mm).
Figure 6 — Limiting dimensions of internal walls for stability
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19 Structural detailing for stability 19.1 Floors Typical ways of connecting floors with walls are shown in Figure 7(a) to Figure 7(c). Where floors are required to provide lateral restraint, reference should be made to Appendix C of BS 5628-1:1978. Suspended timber floors near to the ground should preferably be supported independently by sleeper walls. Where this is not practicable, offsets or corbels from external walls may be used. Suspended timber floors elsewhere may be built into the walls or supported by offsets, corbels or joist hangers. Timber wall plates should not be built into any wall. Unreinforced concrete floors laid on the ground or on fill should not bear on walls, as this may give rise to cracking due to differential movement. The design should ensure that the bearing of all types of floor is not less than 75 mm, taking normal tolerances into account. Concrete floors should normally have a bearing of not less than 90 mm; however, this bearing may be reduced at the discretion of the designer, taking into account relevant factors such as loading, span, tolerances, height of support and the provision of continuity reinforcement. 19.2 Roofs The design should ensure that the roof structure provides adequate lateral restraint for the wall. Typical ways of connecting roofs with walls are shown in Figure 7(d) to Figure 7(h). Reference should also be made to Appendix C of BS 5628-1:1978. Particular care should be taken when detailing the bearings of flat roofs upon walls, to reduce the danger of displacement of the top courses of masonry as a result of thermal movements in the roof and deflection of the structure. Temperature variations may be reduced by providing external insulation or reflective coatings.
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Timber joists and joist hangers should have a minimum bearing of 75 mm on walls. The frogs of bricks should be filled to provide an even bearing. It may be desirable to provide a wall plate in certain cases. Concrete roofs should normally have a bearing of not less than 90 mm. However, this bearing may be reduced at the discretion of the designer, taking into account relevant factors such as loading, span, tolerances, height of support and the provision of continuity reinforcement. Binders or other beams giving rise to concentrated loads on the wall may need to be provided with a padstone or spreader beam (see 18.3). 19.3 Support over openings Masonry should not be supported on window or door frames which are not designed for the purpose. Where lintels are used, these should have adequate bearings, commensurate with the solidity of the support (see 18.3) and the load for which they are designed and in any case not less than 100 mm in length. Lintels should not bear on a short length of cut block. Where possible, the masonry should be set out to provide a full block under a bearing. Pressed steel lintels should have a bearing of not less than 150 mm in length and may need stiffening over the bearing length to resist the total load. Protective measures for steel lintels, including provision of d.p.cs where appropriate, should comply with BS 5977-2. Where composite lintels, e.g. prestressed concrete plank lintels, are used, no chase or hole should be formed in the area comprising the composite section nor should any inclusion, such as joists, be built into this section, with the exception of d.p.c. materials which intrude not more than one-quarter of the width of the bed joint or 30 mm, whichever is the lesser. Installation should follow the recommendations of the manufacturers.
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Figure 7 — Typical ways of connecting floors and roofs
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Figure 7 — Typical ways of connecting floors and roofs (continued)
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Figure 7 — Typical ways of connecting floors and roofs (continued)
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NOTE 1 NOTE 2
Boards should span at least two rafters and be butted up to the wall. The soffit board should be securely fixed to the ladder bracket and should also be a close fit to the wall.
(e) Truss roof without straps Figure 7 — Typical ways of connecting floors and roofs (continued)
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Figure 7 — Typical ways of connecting floors and roofs (continued)
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Figure 7 — Typical ways of connecting floors and roofs (concluded) © BSI 11-1999
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19.4 Anchorages, dowels and fixings Typical anchorages, dowels and fixings are shown in Figure 8.
It is essential to select the correct materials for these components to ensure adequate resistance to corrosion (see clause 8).
Figure 8 — Typical anchorages, dowels and fixings
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Figure 8 — Typical anchorages, dowels and fixings (concluded)
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19.5 Wall ties The leaves of a cavity wall should be tied together by wall ties embedded in the horizontal mortar joints at the time the course is laid, to a minimum depth of 50 mm. The length of the wall tie should be chosen to suit the width between the two leaves. The ties should be placed at a frequency of not less than the values given in Table 9(A) and they should be staggered and evenly distributed. Additional ties should be provided within 225 mm of all openings so that there is one for each 300 mm of height of the opening. Consideration should be given to providing additional flexible ties across the cavity adjacent to movement joints. The choice of the type of tie depends on the cavity width [see Table 9(B)]. In situations of Severe or Very Severe exposure as defined in 21.2, copper alloy or stainless steel ties should be used. In chimneys where masonry bonding is not maintained (see Figure 9) stainless steel ties should be provided at intervals of three courses. 19.6 Provision for services and fittings
The designer should consider the effects of chasing on stability, bearing in mind the recommendations of BS 5628-1, particularly where walls or leaves are constructed of hollow units. In walls or leaves constructed of solid units, the depth of horizontal chases should not normally exceed one-sixth of the thickness of the single leaf at any point, whilst the depth of vertical chases should not normally exceed one-third of the thickness of the single leaf at any point. The cutting of holes up to approximately 300 mm square in the wall to accommodate items of equipment may be permitted. Where heavy fittings are to be fixed to a wall, the effect on the stability of the masonry should be considered. 19.7 Chimneys Where a chimney is not supported by adequate ties or otherwise made secure, its height, measured from the level of the highest point in line with the roof, gutter or other part of the building, and including any pot or flue terminal, should not be more than four and a half times its least width at that level. Typical chimney details are shown in Figure 9 (see also 21.5.8).
When making provision for services and fittings, designers should ensure that none of the functions of the wall are impaired by fixings, chases or holes. Table 9 — Wall ties (A) Spacing of ties Least leaf thickness (one or both)
Type of tie
Cavity width
mm
65 to 90 90 or more
Equivalent no. of ties per square metre
Spacing of ties Horizontally
Vertically
mm
mm
mm
All See Table 9(b)
50 to 75 50 to 150
4.9 2.5
450 900
450 450
(B) Selection of ties Type of tie in BS 1243
Cavity width mm
Increasing strength
28
Increasing flexibility and sound insulation
Vertical twist
150 or less
Double triangle
75 or less
Butterfly
75 or less
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Figure 9 — Typical chimney details
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Figure 9 — Typical chimney details (concluded)
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20 Movement in masonry 20.1 General After construction, buildings are subject to small dimensional changes, which may be caused by one or more of the following factors. a) Change in temperature (see A.4). b) Change in moisture content (see A.5). c) Adsorption of water vapour (see A.5). NOTE Adsorption is the term used to describe the bonding of water molecules to the molecules of the masonry material. It should not be confused with absorption, which refers to the entry of water molecules into the pores of the masonry.
d) Chemical action, e.g. carbonation (see A.6). e) Deflection under loads. f) Ground movement and differential settlement. To guard against dimensional changes occurring as a result of sulphate attack, the recommendations of 22.4 should be followed. In general, because restraints are often present, masonry is not completely free to expand or contract and compressive or tensile forces may develop, and these may lead to bowing or cracking. The risk of bowing is greater where the compressive forces are applied eccentrically, e.g. where panel walls are not supported across their whole thickness. The risk of cracking is increased where there are stress concentrations, for example at openings or at changes in height, thickness or direction of walls, and where stronger mortars than those recommended in clause 22 are used. Masonry units of markedly different characteristics, for example fired-clay and concrete masonry units, should not be bonded, but should be effectively separated by either a vertical or horizontal movement joint or by a slip plane, since their movements are different in magnitude and in kind (see Appendix A). It is essential to consider provision for movement at the design stage. 20.2 Accommodation for movement of adjoining structural members 20.2.1 Walls supported by structural members. Where a wall is built on a suspended floor or beam and is not designed for composite action, it may be necessary to make provision for deflection of the supporting member by providing vertical movement joints or a separation joint at the base of the wall. In the latter case it may be necessary to reinforce the bed joints where tension may occur.
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20.2.2 Walls and partitions beneath structural members. Partitions are normally built up to the underside of a floor, ceiling or roof. However, in circumstances where the partition is designed not to carry any vertical load, it should be separated by a gap or by a layer of resilient material to accommodate the deflections of structural members above it. A cut should be formed between any ceiling and wall plaster or the joint should be masked with a cornice or other cover fillet, which may also be designed to provide lateral restraint to the partition. Consideration should be given to the need for slip planes under the bearings to separate the wall from structural members which can produce a horizontal movement, e.g. longer span concrete lintels. 20.2.3 Panel walls in frame structures 20.2.3.1 General. Panel walls in steel frame and concrete frame buildings should be designed to prevent cracking as a result of stresses generated by differential movement between the panel and the frame. All panels, irrespective of the type of masonry units from which they are built, should be provided with adequate lateral edge restraint (see 18.4). Some particular cases of design to limit the effect of differential movement and yet provide stability of the panel are described in 20.2.3.2 to 20.2.3.4. 20.2.3.2 Panel walls in reinforced concrete frame structures. In external infill panel walls of fired-clay masonry, any expansion will be opposed in the vertical direction to the shrinkage and creep of reinforced concrete columns. Where the panels are built in tightly between horizontal beams and slabs, these opposing movements, if restrained, can cause excessive stresses in the masonry, particularly where they are eccentric, e.g. where the panel overhangs a floor slab. Hence horizontal compressible joints should be provided at each level of intersection of the panel and horizontal elements of the structure. Similar considerations apply to external infill panel walls of calcium silicate or concrete masonry, except that differential movement between the concrete frame and the infill is less, since the long term movement of both will be in the same direction. Provision of movement joints between a panel and a frame may alter the support conditions (see 18.4.2.2) and an alternative means of providing restraint may be necessary. Some forms of suitable restraint are given in 19.4. Vertical movement joints may also be necessary to absorb horizontal movements of panel walls, for example where they pass in front of columns.
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20.2.3.3 Panel walls in steel frame structures. Providing eccentric loads and short returns are avoided, panel walls of fired-clay masonry in multi-storey steel structures can usually be built into, and tied rigidly to, the frame. Concrete and calcium silicate masonry should not be tied rigidly to the frame but it is essential to provide adequate lateral restraint. In frame structures, masonry infill panels which are attached to the frame should be designed to take into account the sway of the structure. This is particularly important in single-storey frame buildings. 20.2.3.4 Panel walls for wind bracing. Where masonry panel walls are provided to form wind bracing in a frame structure, it is essential that they should be built in rigidly to the surrounding framework. The panel should be designed not only to resist the stresses due to the imposed load, but also the stresses which may arise from differential movement between the panel and the frame. 20.2.4 Fired-clay brick slips. When fired-clay brick slips are fixed to the nib or toe of a concrete slab or beam, there is the possibility of vertical stresses acting on the courses of brick slips as a result of both creep and drying shrinkage of the concrete as well as long term vertical expansion of the clay brick infill. Consequently, a compressible flexible joint should be provided between the first course of brick slips and the brickwork beneath, whilst the top course should be protected by a damp-proof membrane in the form of a cavity tray. Similarly, there is some likelihood of horizontal stresses arising as a result of differential movement between the concrete substrate and the brick slips. Accordingly, vertical movement joints should be considered and these should be spaced more frequently than the centres recommended for normal brickwork in 20.3.2 and provided wherever the brick slips join the main structure at piers or columns. The horizontal and vertical movement joints should be formed by a compressible filler and sealed at the face with a suitable sealant (see Figure 13). The width of the joint should normally be 10 mm. 20.3 Accommodation of movement in masonry 20.3.1 Movement joints and slip planes. Movement joints should be designed to accommodate expansion and/or contraction [see Figure 10(a)]. Expansion joints should be filled with easily compressible and resilient material. Joints should be designed so as to be built in as work proceeds and not to be cut into completed work.
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Slip planes should be designed to allow parts of the construction to slide, one in relation to the other, thus reducing shear stresses in the adjacent materials. The slip plane should contain two layers of smooth incompressible sheet material or an applied coating to form a separating membrane. This membrane can often be positioned and formed so as to function also as a flexible d.p.c. The design and positioning of movement joints and slip planes should be carefully considered, making sure that in addition to accommodating movements, such joints or planes do not impair the stability of the wall or any of its functions. Where necessary, dowels strong enough to provide lateral stability should be incorporated. The dowels, which are usually of metal rod or flat strip, should be anchored into the masonry in such a way that longitudinal movement is not restrained [see Figure 8(c)]. Particular care should be taken with the design of movement joints in separating walls, party walls or compartment walls where the efficiency of the wall for sound insulation or as a fire barrier (see clause 24) might be reduced. In external walls, movement joints and slip planes should be sealed, protected or otherwise designed to prevent water penetration (see 20.4). Care should be taken to ensure that fixings and services do not interfere with the performance of the joints or planes. Finishes should be discontinuous at movement joints and slip planes, and fixings and fittings should not tie across the joint. 20.3.2 Provision of movement joints 20.3.2.1 General. The empirical recommendations given in this subclause are applicable to the majority of situations. Movement joints will not normally be required in internal walls in dwellings. The spacing of the first movement joint from an external or internal angle should be not more than half the general spacing and preferably less where the masonry is continuous at the angle, due to the effect of end restraint of the wall panel. For information on basic data and design to accommodate movement, see Appendix A and consult the manufacturers.
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20.3.2.2 Spacing and width of movement joints in fired-clay masonry. In general, unrestrained or lightly restrained unreinforced walls, e.g. parapets and non loaded spandrels built off membrane-type d.p.cs, will expand 1 mm/m during the life of the building, due to thermal and moisture movement changes. The spacing and thickness of movement joints in such walls is governed by the allowable compressibility of fillers and the performance of appropriate sealants. Designers are recommended to consult sealant manufacturers wherever possible, but as a general guide, the width of the joint in millimetres should be about 30 % more than the distance between joints in metres. Thus movement joints at 12 m centres will need to be about 16 mm wide. Where a manufacturer can show evidence from experience that his products, e.g. London Stocks, expand less than 1 mm/m, or will guarantee low expansion, the foregoing guidance may be modified at the designer’s discretion. Experience shows that the expansion of normal storey height walls, as opposed to unrestrained walls, is somewhat less than 1 mm/m and that, in general, expansion reduces with increasing restraint. However, in unreinforced walls spacing between movement joints should never exceed 15 m, in order to avoid cracking due to thermal contraction. Closer spacing may be necessary for the least restrained walls, e.g. parapets. Where bed joint reinforcement is used, it has been found that spacings greater than 15 m are satisfactory but expert advice should be sought. Present evidence suggests that vertical movement of unrestrained walls is of the same order as horizontal movement. 20.3.2.3 Spacing and width of movement joints in calcium silicate masonry. Where possible, calcium silicate masonry should be designed as a series of panels separated by movement joints. The ratio of length to height of the panels should not exceed 3 : 1. As a general rule, vertical joints to accommodate horizontal movement should be provided at intervals of between 7.5 m and 9 m. Movement joints should normally not exceed 10 mm in width and be sealed where necessary.
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In external walls containing openings, movement joints may need to be provided at more frequent intervals or the masonry above and below the opening may need to be reinforced to restrain movement (see 20.5). Particular attention should be paid to low horizontal panels of masonry, for example under windows. 20.3.2.4 Spacing of movement joints in concrete masonry. Where possible, concrete masonry should be designed as a series of panels separated by movement joints. As a general rule, vertical joints to accommodate horizontal movement should be provided at intervals of 6 m. Since there are wide variations in physical properties between different concrete masonry units, some variation in joint spacing is acceptable but it should be noted that the risk of cracking increases if the length of a panel exceeds twice the height. It is, however, always desirable to consult the block manufacturers before using joint spacings greater than 6 m. In external walls containing openings, movement joints may need to be provided at more frequent intervals or the masonry above and below the opening may need to be reinforced to restrain movement (see 20.5). Particular attention should be paid to low horizontal panels of masonry, for example under windows. 20.3.2.5 Placing of movement joints. Features of the building which should be considered when determining joint positions in the masonry are as follows: a) intersecting walls, piers, floors, etc.; b) window and door openings; c) change in height or thickness of the wall [see Figure 10(b)]; d) chases in the wall [see Figure 10(b)]; e) movement joints in the building or in floor slabs [see Figure 10(b)]. Areas above doors and above or below windows may be reinforced to distribute stresses (see 20.5).
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Figure 10 — Movement joints
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Figure 10 — Movement joints (concluded)
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20.4 Sealing of movement joints
21 Exclusion of moisture
The width and depth of seal for movement joints is important. To ensure adequate bond to the masonry, the depth of seal should be at least 10 mm. Certain single-part moisture-cured sealants are best used in joints of small cross section due to their excessive curing time in thick sections. Optimum performance in butt joints is obtained when the width to depth ratio of the sealant bead lies within the range 2 : 1 to 1 : 1, for elastoplastic sealants (including one and two part polysulphides), or the range 1 : 1 to 1 : 2 for elastoplastic sealants (including cross-linked butyl rubber). The sealant should be applied against a firm backing so that it is forced against the sides of the joint under sufficient pressure to ensure good adhesion. The back-up material should be resilient and not adhere to or react with the sealant. The compressibility of the sealant back-up/joint filler is possibly the most critical factor in the design of an adequate joint for fired-clay brickwork. A pressure of about 0.1 N/mm2 should be sufficient to compress the material to 50 % of its original thickness. Flexible cellular polyethylene, cellular polyurethane or foam rubbers are the most satisfactory materials. Hemp, fibreboard, cork and similar materials should not be used for expansion joints in fired-clay brickwork. The width of the joint should be sufficient to accommodate the movements, both reversible and irreversible, without damage to the seal. Hence the width of the joints should be related to the spacing of the joints. Further guidance on the selection of sealants is given in BS 6213.
21.1 General
20.5 Reinforcement Reinforcement may be used to control cracking, which may occur in areas of masonry above or below openings where the vertical cross-sectional area of the masonry is much less than that of the masonry on either side. The reinforcement should be long enough to distribute the stress to a position where the vertical cross-sectional area is able to accommodate it, and should be adequately protected against corrosion (see 22.7.2).
2) Available
36
Rain penetration is one of the commonest building defects (see BRE Digest 176, “Failure patterns and implications” 19752). It is essential to consider carefully design, detailing, workmanship and materials in relation to local exposure conditions if the incidence of rain penetration is to be minimized. An assessment of the local wind-driven rain index should be made (see 21.2). When determining the likely exposure of a building, the most exposed part should be given particular attention and this may affect decisions concerning the choice of design and materials for the whole of the building. Using the guidance on resistance to rain penetration of different forms of construction and the factors affecting rain resistance given in 21.3, the designer should select a construction appropriate to the local wind-driven rain index, paying due regard to the importance of correct detailing and workmanship. In cavity walls, some water will inevitably penetrate the outer masonry leaf in prolonged periods of wind-driven rain but proper design and positioning of the damp-proof systems (see 21.4) will minimize the risk of penetration further into the building. 21.2 Classification of exposure to local wind-driven rain The quantity of rain falling on a vertical surface, such as a wall, at any point depends on both the intensity of the rainfall and the wind speed. The BRE Report “Driving Rain Index” 19762) postulated that the quantity of rain falling on a vertical surface, such as a wall, was proportional to the quantity falling on a horizontal surface and to the local wind speed, and incorporated maps of an annual wind-driven rain index, which is the product of the annual local rainfall and the annual average airfield wind speed. Rainfall varies considerably across the country but is largely unaffected by local features. Conversely, the general wind speed does not change so much across the country but is very much affected by local features, such as the spacing and height of surrounding trees and buildings and whether the ground is flat or steeply rising. Appropriate correction factors to convert the annual wind-driven rain index to the local annual index were computed by the Building Research Establishment (BRE).
from the Building Research Station, Garston, Watford, Herts WD2 7JR.
© BSI 11-1999
BS 5628-3:1985
With the advent of computer analysis of meteorological data, the Meteorological Office was able to produce much more realistic values, based on the fact that heavy rainfall was usually associated with strong winds. To enable designs for “worst expected” conditions to be based on the conditions prevailing in a spell of bad weather, maps were prepared showing the quantity of wind-driven rain falling on vertical surfaces during the worst likely spell of bad weather in any three year period. This data forms the basis for the local spell index method described in DD 93. Table 10 gives exposure categories defined either in terms of the local spell indices calculated using DD 93 or in terms of the exposure categories that were given in CP 121-1:1973, which were based on the BRE report. These indices are not precise, since they are derived from inherently variable meteorological data. This variability has been reflected in the definitions of the exposure categories by overlapping the indices at their boundaries. Where exposure categories overlap (see Figure 11), the designer should decide which is the most appropriate category for the particular case, using local knowledge and experience. Examples of constructions suitable for particular exposure categories are given in 21.3. Table 10 — Classification of exposure to local wind-driven rain 1 Exposure category
2
3
Local spell Exposure index calculated category in as described in CP 121-1:1973 DD 93 (see note)
Very Severe
L/m2 per spell 98 and over
Severe
68 to 123
Moderate/Severe
46 to 85
Sheltered/Moderate 29 to 58 Sheltered
19 to 37
Very Sheltered
24 or less
Severe
Moderate Sheltered
NOTE CP 121-1:1973 defined three exposure categories, namely Severe, Moderate and Sheltered, corresponding to values of Lacy’s Annual Mean Driving Rain Index > 7 m2/s, 3 m2/s to 7 m2/s and < 3 m2/s respectively (see BRE Report “Driving Rain Index” 1976a Developments since the publication of that code, such as the introduction of insulation into cavity walls and the advent of improved meteorological data, have made it necessary to increase the number of exposure categories. a
Available from the Building Research Station, Garston, Watford, Herts WD2 7JR.
© BSI 11-1999
21.3 Selection of external constructions to resist rain penetration 21.3.1 General. The following factors affecting the resistance to wind-driven rain of masonry constructions should be considered in relation to other functions of the wall such as strength, durability, sound and thermal insulation: a) presence of applied external surface finishes (see 21.3.2.1); b) quality of workmanship achieved on site (see 21.3.2.2); c) type of masonry unit (see 21.3.3); d) mortar composition (see 21.3.2.3); e) joint finish (see 21.3.2.4); f) joint profile (see 21.3.2.4); g) thickness of the leaf (see 21.3.2.5); h) presence of a cavity; i) width of air space within any cavity (see 21.3.2.6); j) architectural features (see 21.3.2.7); k) presence and type of any cavity insulation (see 21.3.2.8). NOTE There has been no intention to list these factors in order of importance.
21.3.2 Detailed considerations 21.3.2.1 Applied external surface finishes. For both single-leaf and cavity walls, total resistance to rain penetration can be achieved only by cladding with metal, plastics materials, shingles, slates, tiling or timber. Rendering can substantially enhance the rain resistance of both single-leaf and cavity walls. It is essential, however, to select the right type of mix, thickness and number of coats and to detail the wall properly to minimize cracking, which may otherwise reduce the effectiveness of the rendering against rain penetration. The recommendations of BS 5262 should be followed. The use of masonry paint systems (see BS 6150) and other proprietary external finishes including colourless treatments, e.g. silicone-based water repellents (see BS 3826), may increase the resistance to rain penetration. However, these surface treatments may also reduce the rate of evaporation of any water from the wall and, depending upon exposure conditions, the quantity of water in the wall may therefore increase. In extreme cases this may be enough to saturate certain types of fired-clay masonry sufficiently for frost damage to take place (see clause 22). Surface treatments also have a limited life (see clause 16 of BS 6270-1:1982).
37
BS 5628-3:1985
Figure 11 — Overlap between exposure categories
38
© BSI 11-1999
BS 5628-3:1985
21.3.2.4 Joint finish and profile. Whatever the type Complete cavity fill may inhibit the drying out of of masonry, it is essential to fill all the joints to any moisture which penetrates the external finish. minimize the risk of rain penetration. Tooled mortar The presence of moisture could lead to sulphate joints are more resistant to rain penetration than and/or frost action (see 22.1) on the mortar and/or joints which have not been tooled. Recessed joints finish with some fired-clay masonry backing increase the risk of water penetration. materials. 21.3.2.5 Single-leaf walls. The resistance to rain 21.3.2.2 Quality of workmanship. The quality of penetration of single-leaf walls of calcium silicate workmanship achieved on site is an important and fired-clay masonry without rendering or factor affecting rain penetration. Some masonry cladding is dependent upon both the thickness and external leaves require more care in construction than others. For example, consider lower and higher absorptive capacity of the masonry units, whereas the rain resistance of dense concrete masonry is absorption fired-clay masonry units. For fired-clay dependent more on thickness. Table 11(A) shows the masonry units of lower absorption, e.g. absorption recommended minimum thicknesses for both by mass of 5 % (m/m)3), the water is shed by the rendered and unrendered walls. glass-like surface (the “raincoat effect”). Where joints have not been completely filled, the film of NOTE The thickness of the outer leaf of a cavity wall will water on the surface will rapidly penetrate the wall. similarly affect its rain resistance but Table 11(A) does not apply to cavity constructions, since it takes no account of the cavity. For fired-clay masonry units of higher absorption, Where hollow blocks are used in external walls, the e.g. 25 % (m/m)3), the wall acts like a sponge and absorbs the water falling on it (the “overcoat effect”). use of shell bedding (see 2.25) may reduce rain penetration to the inner surface and so give some of Whilst all mortar joints should always be filled (see 21.3.2.4), minor imperfections which can occur the advantages of cavity wall construction. are not so critical, except in conditions of Very 21.3.2.6 Unfilled cavity walls. In unfilled cavity Severe exposure, because most periods of walls, it is the air space between the two leaves, wind-driven rain are not long enough for the wall to i.e. the clear cavity, which is intended to prevent become saturated, and thus permit rain water passing from the outer leaf to the inner leaf. penetration, before the intervention of a dry period. In most situations, a 50 mm air space is satisfactory but where there is an increased risk of rain 21.3.2.3 Mortar composition. For lower absorption penetration, consideration should be given to the fired-clay masonry units, the designer should use of wider cavities. Where the cavity is consider using one of the less permeable mortars unavoidably bridged, e.g. at window and door such as designation i) and ii). For other types of masonry unit, the selection of mortar is governed by openings, special precautions are necessary other factors such as accommodation of movement, (see 21.4). For filled cavity walls see 21.3.2.8. durability and strength. Table 11 — Assessment of resistance to rain penetration (A) Thickness of single-leaf walls with or without rendering Exposure category
Minimum thickness of masonry (excluding rendering and finishes) (see note 1) Clay and calcium silicate masonry Rendered
Unrendered (see note 2)
Concrete masonry Rendered (dense concrete)
Rendered (lightweight aggregate or autoclaved aerated concrete)
Very Severe
Not recommended. Cladding should be used
Severe
328
Moderate/Severe
215
Sheltered/Moderate Sheltered Very Sheltered
190 90 90
mm
mm
Not recommended Not recommended 440 328 190
mm
mm
250
215
215
190
190 90 90
140 90 90
Unrendered (see note 2)
mm
Not recommended Not recommended 440 328 190
NOTE 1 Thickness of masonry is based on work sizes of masonry units i.e. tolerances are not included. NOTE 2 Thicknesses of unrendered walls are based on the use of tooled joints filled completely with cement : lime : sand mortar. NOTE 3 This table is intended to give guidance on the selection of forms of construction from the point of view of resistance to rain penetration only but other factors such as durability should be considered. 3) Measured
as described in BS 3921.
© BSI 11-1999
39
BS 5628-3:1985
21.3.2.8 Filled cavity walls. Filling the complete cavity of a cavity wall with thermal insulation will increase the risk of rain penetration through the wall (see BRE Digest 236 19804)). In Table 11(B) insulants are divided into: a) type A insulants, such as mineral fibre (see BS 6232) or polystyrene beads, which should not be subjected to exposure conditions more severe than those recommended for the equivalent unfilled wall; b) type B insulants, such as urea formaldehyde foam (see BS 5618) and granular plastics fills, which are subject to various additional restrictions related to the local exposure conditions and the type of construction.
At present there is insufficient information available to enable recommendations to be made regarding the effectiveness of the inner leaf of a cavity wall in resisting water penetration. Therefore, in general, designers should not rely on the inner leaf of a cavity wall to resist rain penetration. The principal factors affecting rain penetration of cavity walls are given in Table 11(B). 21.3.2.7 Architectural features. Architectural features can play an important part in reducing the risk of rain penetration. The designer should always consider the effects that his design will have on the tendency for the external masonry to be wetted more than by the incident rainfall (see 22.5). He can reduce the degree of wetting by ensuring that water is thrown clear of the walls by adequate overhangs and drips and by providing drainage to take the water away from the masonry. Large areas of glazing or cladding give rise to very large amounts of surface run-off water which can cause excessive wetting of the masonry below and possible water penetration problems.
NOTE The risk of rain penetration for all insulants will be reduced by using a cavity wider than 50 mm.
Partial filling of a cavity wall (i.e. filling part of the width of a cavity with insulant placed against the inner leaf) does not affect the resistance to wind-driven rain of the wall, providing the width of the remaining air space is not less than 50 mm. The use of widths less than this increases the risk of rain penetration and should therefore be subject to various restrictions related to the local exposure conditions and type of construction. 21.3.3 Examples of cavity wall external leaf constructions suitable for particular exposure categories. When choosing a cavity wall external leaf construction suitable for a particular exposure category, Table 11(B) may be used with discretion as a starting point for the designer. Table 11 — Assessment of resistance to rain penetration
(B) Factors affecting rain penetration of cavity walls Factor affecting rain penetration
Increasing probability of rain penetration in the direction of the arrow
Applied external finish (see 21.3.2.1)
Cladding
Rendering Other (e.g. masonry paint, water repellent)
Mortar composition (see 21.3.2.3)
Cement : lime : sand
Mortar joint finish and profile (see 21.3.2.4)
Bucket handle, weathered, etc.
Air space (clear cavity) (see 21.3.2.6)
Over 50 mm
Insulation (see 21.3.2.8)
None
Cement : sand plus plasticizer or masonry: cement : sand Flush 50 mm
Partial filling with 50 mm air space
Recessed, tooled 25 mm
Filled with type A insulant (50 mm cavity)
Recessed, untooled None [see Table 11(A)] Filled with type B insulant (50 mm cavity)
NOTE 4 It is essential to read this table in conjunction with 21.3.2 and 21.3.3. In particular, the table does not take account of quality of workmanship (see 21.3.2.2) or the effect of architectural features (see 21.3.2.7).
4) Available
40
from the Building Research Station, Garston, Watford, Herts WD2 7JR.
© BSI 11-1999
BS 5628-3:1985
In general, the more severe the exposure category, the more items from the left-hand side of the table should be selected. Conversely, the more items from the right-hand side of the table the designer wishes to use, the less severe the exposure category in which the building construction will be satisfactory. Local experience and conditions should always be taken into account when making a decision on the suitability of a particular construction. Some examples of cavity wall external leaf constructions suitable for particular exposure categories are as follows. Example 1. Clay brickwork. Cement : lime : sand mortar, designation i), ii) or iii). Tooled and weathered or bucket handled joints. 50 mm clear cavity, no cavity insulation. Maximum exposure category: Severe5). Example 2. Clay brickwork. Cement : sand mortar plus plasticiser, designation i), ii) or iii). Tooled and weathered or bucket handled joints. 50 mm clear cavity, no cavity insulation. Maximum exposure category: Moderate/Severe5). Example 3. Clay brickwork. Cement : sand mortar plus plasticiser, designation i), ii) or iii). Tooled and weathered or bucket handled joints. 50 mm clear cavity, cavity filled with type B insulant. Maximum exposure category: Sheltered/Moderate5). Example 4. Clay brickwork. Cement : lime : sand mortar, designation ii) or iii). Raked and untooled joints. 50 mm cavity filled with type B insulant. Maximum exposure category: Sheltered5). Example 5. Dense concrete blockwork. Cement : lime : sand mortar, designation iii). Tooled and weathered or bucket handled joints. 50 mm clear cavity, no cavity insulation. Maximum exposure category: Moderate/Severe. NOTE Certain types of dense concrete blocks may be suitable for Severe exposure category. The manufacturer should be consulted.
Example 6. Concrete brickwork. Cement : lime : sand mortar, designation iii). Tooled and weathered or bucket handled joints. 50 mm clear cavity, no cavity insulation. Maximum exposure category: Severe.
Example 7. Concrete brickwork. Cement : sand mortar plus plasticiser, designation i), ii) or iii). Tooled and weathered or bucket handled joints. 50 mm clear cavity, no cavity insulation. Maximum exposure category: Moderate/Severe. Example 8. Calcium silicate brickwork. Cement : lime : sand mortar, designation iii). Tooled and weathered or bucket handled joints. 50 mm clear cavity, no cavity insulation. Maximum exposure category: Severe. Example 9. Dense concrete blockwork. Cement : lime : sand mortar, designation iii). Tooled and weathered or bucket handled joints. 50 mm clear cavity, no cavity insulation. Rendered. Joint finish and profile as required for rendering. Maximum exposure category: Severe. 21.4 Damp-proof courses and cavity trays 21.4.1 A damp-proof course (d.p.c.) in a building is intended to provide a barrier to the passage of water from the exterior of the building to the interior, or from the ground to the structure, or from one part of the structure to another. The passage of water may be horizontal, upwards, or downwards. Where the d.p.c. is intended to prevent the upward movement of water due to capillary action, joints may be lapped without sealing. However, where water is moving in a downwards direction, the joints in the d.p.c. should be sealed. 21.4.2 In cavity walls, d.p.c. design should be based on the assumption that rain will penetrate the outer leaf of the wall and run down the inside of the outer leaf. Where the cavity is bridged, e.g. by cavity fill, lintels, structural beams, floor slabs or pipes, there is a danger that water will be conducted across it to cause dampness inside the building. To avoid this problem, it is essential that watertight cavity trays are provided above all bridges of the cavity (other than wall ties), so that water is diverted to the outer leaf or clear of the bridges. 21.4.3 To ensure adequate performance, d.p.cs and cavity trays should have the following material properties: a) an expected life at least equal to that of the building; b) resistance to compression without extrusion; c) resistance to sliding where necessary; d) adhesion to units and mortar where necessary;
5) For
clay brickwork built to the quality of workmanship recommended in this code, the maximum exposure category will be comparable for all absorption levels of brick. However, the mechanism of resistance to rain penetration may differ (see 21.3.2.2)
© BSI 11-1999
41
Material A. Flexible
Minimum mass kg/m2
Minimum thickness
1.8
mm
Joint treatment to prevent water moving Upward Downward
Lapped at Welted least 100 mm
Liability to extrusion
Lead complying with BS 1178
code no. 4
Copper complying with BS 2870 grades C 104 or C106 in the O condition Bitumen Hessian base (class A of BS 6398) Fibre base (class B of BS 6398) Asbestos base (class C of BS 6398) Hessian base and lead (class D of BS 6398) Fibre base and lead (class E of BS 6398) Asbestos base and lead (class F of BS 6398) High bond strength asbestos base
Approx. 0.25 2.28
Lapped at Welded or least 100 mm welted
3.8
—
3.3
—
3.8
—
4.4
—
Lapped at Lapped at Likely to extrude least 100 mm least 100 m under heat and m and sealed moderate pressure but this is unlikely to affect resistance to moisture penetration
4.4 4.9
—
2.2
—
Approx. 0.46 Polyethylene, low 0.5 density (0.915 g/L to 0.925 g/L) complying with BS 6515
Welted Lapped for distance at least equal to width of d.p.c.
Durability
Not under pressure Corrodes in contact with met in normal mortars. Protect with construction bitumen or bitumen paint of heavy consistency applied to the corrosion-producing surface and to both surfaces of the lead Not under pressure Highly resistant to corrosion. If soluble salts met in normal are present, protect as for construction lead The hessian or fibre may decay but this does not affect efficiency if the bitumen remains undisturbed. Classes D, E and F are most suitable for buildings that are intended to have a very long life or where there is risk of movement
Not under pressure No evidence of deterioration in contact met in normal with other building construction materials
Other considerations
May be easily worked to required shape but this is a slow process
May stain masonry. Not easy to work on site, so not suitable for cavity trays Materials should be unrolled with care. In cold weather, warm before use. When used as a cavity tray, the d.p.c, should be fully supported For further guidance see Appendix B of BS 6398:1983
© BSI 11-1999
Should follow the recommendations in Appendix C of BS 6398:1983 Accommodates considerable lateral movement. When used as a cavity tray, may be difficult to hold in place and may need bedding in mastic for the full thickness of the outer leaf, to prevent rain penetration. Not suitable for use where compressive stress is low, e.g. under copings
BS 5628-3:1985
42
Table 12 — Physical properties and performance of materials for d.p.cs
© BSI 11-1999
Table 12 — Physical properties and performance of materials for d.p.cs Material
Minimum mass
Minimum thickness
kg/m2
mm
A (continued)
Bitumen polymer and pitch polymer
Approx. 1.10 1.5
Joint treatment to prevent water moving Upward
Liability to extrusion
Downward
Durability
Not under pressure Unlikely to be impaired Lapped at Lapped at by any movements least 100 mm least 100 mm met in normal normally occurring up to construction and sealed the point of failure of the wall
Other considerations
Accommodates considerable lateral movement. When used as a cavity tray, preformed cloaks should be used, e.g. at changes of level and junctions
B. Semi-rigid
— Mastic asphalt complying with BS 1097 or BS 6577 of hardness appropriate to conditions
12
No joint problems
No joint problems
Liable to extrude No deterioration under pressures above 0.65 N/mm2
To provide key for mortar below next course of brickwork, up to 35 % grit should be beaten into asphalt immediately after application and left proud of surface. Alternatively the surface should be scored whilst still warm
No joint problems
No joint problems
Not extruded
Resin content should be about 15 %. The appropriate hardener should be used Particularly appropriate where d.p.c. is required to transmit tension, e.g. in freestanding walls
C. Rigid
—
6.0
D.p.c. brick complying with BS 3921
—
Slate complying with BS 743
—
Two courses, No joint laid to break problems joint, bedded in 1 : 3 Portland cement : sand Two courses, No joint laid to break problems joint, bedded in 1 : 3 Portland cement : sand
No evidence of deterioration in contact with other materials
Not suitable —
No deterioration
Not suitable —
No deterioration
—
43
BS 5628-3:1985
Epoxy resin/sand
BS 5628-3:1985
e) resistance to accidental damage during installation and subsequent building operations; f) workability at temperatures normally encountered during building operations, with particular regard to ease of forming and sealing joints, fabricating junctions, steps and stop ends, and ability to retain shape. Table 12 gives information on performance of individual materials currently used for d.p.cs. 21.4.4 Wherever possible, the part of the cavity tray which bridges the cavity should be continuously supported. It is particularly important to provide support at joints so as to facilitate their formation. 21.4.5 Detailed three-dimensional drawings should be made of all junctions, steps, angles and stop ends, to enable fabrication either on or off site. Typical details are given in 21.5. Many common details cannot be formed satisfactorily on site, unless they are fabricated in lead. If materials other than lead are to be used in these complex situations, then pre-formed cloaks should be specified, so as to restrict the site operation to simple jointing only. 21.4.6 It is essential to form weepholes in the outer leaf immediately above the cavity tray. These may be formed by leaving open perpend joints at not greater than 1 m intervals in the course of units immediately above the cavity tray, with not less than two weepholes over each opening (see 21.5.5). Where cavity filling is anticipated, consideration should be given to reducing the spacing of weepholes. 21.4.7 D.p.cs should extend through the full thickness of the wall or leaf, and preferably project beyond the external face. It is essential to prevent penetration of water beneath the d.p.c., which can occur if it is placed on an irregular mortar or concrete bed. D.p.cs should be laid on a smooth bed of fresh mortar, unless they are required to accommodate differential sliding movements between the units on either side of them, in which case the mortar bed should be trowelled smooth and allowed to set, and then cleaned off before the d.p.c. is laid. It is essential not to use coarse aggregates which might damage the d.p.c. D.p.cs and cavity trays should not be pierced by services, reinforcement, fixings, etc. A d.p.c. should not be bridged by pointing, rendering, plastering, tiling, etc.
21.5.2 Immediately above ground level. In every external wall, a d.p.c. should be provided at least 150 mm above the finished level of the external ground or paving. To prevent the transference of moisture from external walls into solid floors, the damp-proof membrane in the floor, and the d.p.c. in the wall, should overlap and be sealed. In cavity work, the cavity should be filled to ground level with fine concrete, and weepholes should be left in the perpends of the outer leaf at not greater than 1 m intervals immediately above the top of this fine concrete. 21.5.3 Under sills. All pervious or jointed sills or sub-sills should be provided with a d.p.c. for the full length and width of the sill bed. The d.p.c. should overlap the vertical d.p.cs at the jambs of the openings [see Figure 12(a) and Figure 12(b)]. Where the sill is in contact with the backing, the d.p.c. should be turned up at the back and ends for the full depth of the sill. 21.5.4 At jambs of openings. Where a cavity wall is closed at the jambs of openings by masonry, a vertical d.p.c. should be inserted to separate the inner and outer parts of the wall and should extend into the cavity at least 25 mm beyond the width of the closer [see Figure 12(a)]. NOTE Preformed cavity closers are available but experience of their use is limited. Where they are used, care should be taken in detailing junctions with d.p.cs.
Any frame should be so placed as to avoid transmitting water past the d.p.c. and, in the case of timber frames, preferably so as to protect the timber from any damp units. Where the frame is to be built in, the d.p.c. should be secured to the frame before building in [see Figure 12(c)]. If the frame is to be fixed later, the d.p.c. should be left projecting. Vertical d.p.cs at openings should be positioned to overlap with a horizontal d.p.c. at the sill of the opening (see Figure 12) and to be overlapped by horizontal d.p.cs at the head. In single-leaf walls, a vertical d.p.c. similar to that in a cavity wall should be provided at jambs of openings to ensure resistance to rain penetration at least as good as that of the wall itself. Alternatively, this can be accomplished by rendering the external surfaces of the jamb.
21.5 Positioning of d.p.cs 21.5.1 Below ground level. Horizontal and vertical d.p.cs are required where the lowest floor of the building is below ground level. It may be necessary in this situation to consider tanking (see CP 102).
44
© BSI 11-1999
BS 5628-3:1985
21.5.5 Over openings. In cavity walls, cavity trays with stop ends should be provided over all openings (including small openings for ducts, services, etc.), unless they are well protected by building features, such as overhanging eaves. This may be difficult to achieve in arches (see 27.6). The cavity tray should step down or slope across the cavity towards the external leaf and, preferably, terminate in a small drip on the external face of the wall. Not less than two weepholes should be provided in the outer leaf in the perpends of the course above the cavity tray. Consideration should be given to the detail of the junction between the vertical d.p.c. in the jamb and the cavity tray over the opening to ensure continuity of damp-proof measures [see Figure 12(d) and Figure 12(e)]. 21.5.6 At balcony thresholds. Where balconies or patios are formed by an extension of the structural floor or the roof of a room below, difficult waterproofing problems can arise unless the details are carefully considered. An example of a suitable junction between the cavity tray, sill d.p.c. and vertical d.p.c is shown in Figure 12(f). Such a junction should be carefully detailed for the particular location and, unless made of malleable metal, should be fabricated off-site by specialists. 21.5.7 In parapets. A d.p.c. should be provided at a height of not less than 150 mm above the abutment of a roof, to form a moisture-resisting continuity with the flashing to the roof, and should extend to form a projecting drip at the external face of the parapet. In a cavity parapet wall, a d.p.c. or cavity tray should be provided, stepped down at least 150 mm towards the inner or outer part of the wall [see Figure 12(g)]. The designer should carefully consider which way to slope the d.p.c. in a given case. If sloped outwards, the d.p.c. will direct water towards the outer face, which may cause staining. If sloped inwards, moisture may travel along the underside of the d.p.c. and gain access to the underside of the roof covering and interior of the building. In addition to weepholes (see 21.4.6), a d.p.c. should be provided under the coping, with rigid support where necessary. It should be noted that the d.p.c. or cavity tray structurally separates the parapet from the wall beneath, and the coping from the parapet. Structural stability of the parapet should be considered in accordance with 18.4.1.
© BSI 11-1999
21.5.8 Chimneys. Chimneys should preferably be built in cavity wall construction from the foundation to the chimney terminal. D.p.cs should be provided to prevent the downward passage of water into the interior of the building. In principle, the aim should be to provide a horizontal d.p.c. through the thickness of the chimney wall with an upturn at the inner face, which is continuous with the vertical flashing at the intersection with the roof (see Figure 9). This is possible with flat, or very shallow pitched roofs. However, the junction is more complex with steeper pitched roofs. The d.p.c. through the chimney stack should be stepped to correspond with, and be continuous with, the stepped flashing to pitched roofs. However, if the chimney stack walls are only 100 mm thick, rain will almost certainly penetrate the chimney stack and run down the internal surface. If the chimney is set in an internal partition or party wall and the roof is steeply pitched, the masonry may dry out in the roof space, particularly if it is well ventilated. However, with lower pitched roofs the chimney stack should either be built 200 mm or 215 mm thick, or a d.p.c. provided in the chimney stack within the roof space to prevent moisture getting into the masonry below the ceiling. It should be noted that a sheet d.p.c. at the point of intersection with the roof structurally separates the masonry, and the stability of the chimney stack and its resistance to lateral wind loading needs to be considered. A horizontal d.p.c. consisting of two courses of d.p.c. bricks bedded in designation i) mortar for clay brickwork, or two courses of slates bedded in designation i) mortar for calcium silicate or concrete bricks, is often satisfactory. A horizontal d.p.c. should always be provided at the top of the stack. Where a chimney stack is incorporated in an outer cavity wall, preferably the outer leaf and cavity should be continuous around the chimney stack for the full height of the outer wall and then completely surround the chimney stack where it projects above the roof. Corbelling from the chimney breast may be necessary below the roof line, to support the outer leaf at the sides and back of the chimney stack. Chimney stacks built in cavity work should contain a stepped d.p.c. in the outer leaf, continuous with the stepped flashing at the abutment with the roof. In exposed areas, consideration should be given to a chimney tray. This should be of a material stiff enough to form a cavity tray without being built into the inner leaf, thus allowing structural continuity.
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21.6 Flashings and weatherings The material to be used should be sufficiently malleable to permit dressing into shape, but sufficiently stiff to maintain its shape and to resist lifting by the wind. The material should be selected with due regard to the likelihood of corrosion. Metal flashings other than lead should, preferably, be pre-formed. Flashings should be bedded into the work a minimum of 25 mm, and be provided with welted, or otherwise sealed, joints, or adequate overlaps. Flashings should preferably be built in as the work proceeds to avoid any damage to d.p.cs. 21.7 Cappings and copings Chimney terminals, freestanding walls, including parapet walls [see Figure 12(g)] and retaining walls exposed to the weather, should preferably be provided with a coping. The coping (see 2.5) may be a preformed unit or it may be built up using creasing tiles. In either case, the drip edge(s) should be positioned a minimum of 40 mm away from the face(s) of the wall. Where for aesthetic or other reasons a capping (see 2.2) is used, special care is needed in the choice of materials, both for the capping and for the walling beneath (see clause 22). Where the coping or capping is jointed, a continuous d.p.c., bedded in designation i) mortar, for fired-clay units, or designation ii) mortar, for calcium silicate or concrete units, should be provided. Where cappings are used, the d.p.c. may be positioned two courses down rather than immediately below the capping course, in order to obtain greater weight on the d.p.c.. Alternatively, a flashing designed to throw rainwater clear of the walling beneath may be built into the joint.
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Consideration should be given to copings being displaced, e.g. by lateral loads, and to the possibility of vandalism. L-shaped copings and clip-over copings may be more satisfactory in these situations. Where necessary, copings should be dowelled or joggle-jointed together, or suitably fixed down, but consideration has to be given to provision for movement in long coping runs. Additional movement joints may be required in cappings and copings, owing to increased solar absorption (see clause 20). 21.8 External wall becoming an internal wall When an external wall becomes an internal wall, as in the case of a stepped terrace of houses, a cavity gutter should be used to drain the cavity. Where a pitched roof abuts such a wall, a stepped cavity tray will be necessary, to follow the profile of the roof [see Figure 12(h)]. Pre-formed tray profiles should, preferably, be used, and the joints should be sealed. 21.9 Structural frames Where masonry is supported by a structural frame, particular attention should be paid to the detailing of d.p.cs to ensure their continuity. Where cavity brickwork is supported on an edge beam, or on a floor slab, a cavity tray should be used to prevent moisture penetration into the structure. Where a column, or other structural member, obstructs the cavity of the wall, the cavity tray should be continuous around the member. When a structural member bridges the cavity, a vertical d.p.c. should be included between the structural member and the external leaf, and stop ends formed in the cavity tray [see Figure 12(i)].
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Figure 12 — Damp-proof systems © BSI 11-1999
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Figure 12 — Damp-proof systems (continued)
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Figure 12 — Damp-proof systems (continued) © BSI 11-1999
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Figure 12 — Damp-proof systems (continued)
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Figure 12 — Damp-proof systems (continued)
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Figure 12 — Damp-proof systems (continued)
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Figure 12 — Damp-proof systems (continued)
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54 © BSI 11-1999
Figure 12 — Damp-proof systems (continued)
BS 5628-3:1985
NOTE
All discontinuities in cavity trays to be given stop ends to prevent water discharging behind the tray.
(i) Structural frames Figure 12 — Damp-proof systems (concluded)
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22 Durability 22.1 General 22.1.1 A major factor influencing the durability of masonry is the degree to which it becomes saturated with water. It may become saturated directly by rainfall, indirectly by water moving upwards from the foundations or laterally from retained material as in a retaining wall. External masonry is much less likely to become saturated where projecting features have been provided to shed run-off water clear of the walling. Examples of such features are: a) protection to wall heads by roof overhangs or copings; b) projecting throated sills; c) bell mouths to rendering and similar features at the base of tile hanging and other impermeable cladding. It should be noted that conventional weathering details may not protect walls sufficiently in situations of Severe or Very Severe exposure as defined in 21.2. Recessing of the joints may increase water intake and application of an initially impervious finish, e.g. of masonry paint, tiling, or a dense rendering may lead to entrapment of moisture if imperfections develop or if water is able to get behind the finish by any path. External masonry will generally be maintained in a drier condition by a moderately porous uncracked rendering complying with BS 5262 or by a ventilated cladding such as slate or tile hanging, by weather-boarding, and by panels of various materials, e.g. of plastics, timber or metal. 22.1.2 Frost may damage both masonry units and mortar, depending upon their susceptibility to such damage on freezing in the saturated condition. Masonry is particularly at risk when construction takes place during the winter. Masonry units in stacks and uncompleted masonry may become saturated unless adequate protection is provided (see clause 35). In addition, when masonry remains wet for long periods of time and soluble sulphates are present in sufficient quantities from fired-clay bricks, sulphate attack on the mortar joints and other materials containing Portland cement may arise (see 22.4). 22.1.3 The durability of masonry depends only upon the characteristics of the masonry units and the mortar, particularly as regards resistance to frost and to chemical attack. The following factors affect the susceptibility of the masonry to damage. a) Exposure to the weather or to other sources of water (see 22.2).
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b) Exposure to aggressive conditions from all sources including the ground (see 22.3 and 22.4). c) The adequacy of methods taken to prevent the masonry from becoming saturated both in terms of design (see 22.5) and workmanship. Particular attention should be paid to the choice of masonry units and mortar in the following and similar situations where the masonry is likely to become and may remain saturated for long periods of time. 1) In chimney terminals, sills, copings and cappings. 2) In freestanding and retaining walls, parapets and chimney stacks. 3) Below d.p.c. at or near ground level and in foundations, manholes and inspection chambers. The degree to which masonry used below d.p.c. at or near ground level becomes saturated will vary according to the site. The masonry materials will be far less prone to problems on a site that is well-drained and dry. Where a site is wet, and/or the masonry at or near ground level may be subject to saturation, particular care should be taken in the choice of materials. It is good practice to ensure that concrete and paved surrounds do not direct water into the masonry. Where there is more than 150 mm of masonry exposed between d.p.c. and finished ground level, e.g. on sloping sites, the inner leaf of such masonry may act as an earth-retaining wall. As a result considerable quantities of water may be transferred into the walling. There is thus an increased risk of frost and sulphate attack, efflorescence, lime leaching and staining of the outer leaf. The application of a waterproofing treatment to the face of the masonry in contact with the ground will minimize or obviate such problems. 22.2 Exposure to the weather A good indication of the general exposure of the site to wind-driven rain may be obtained as described in clause 21. However, it should be appreciated that different elements in the same building may be subjected to different degrees of exposure. In areas of Severe or Very Severe exposure, it is particularly important that the masonry is protected by overhangs and other projecting features (see 22.1). If such protective features are omitted for aesthetic reasons, the possible effects of the increased exposure of the masonry to wetting should be considered (see 22.5).
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22.3 Frost action
22.4 Sulphate attack
22.3.1 Night frosts are common even in mild winters and it is important to protect the masonry units and the newly erected masonry adequately, both from saturation and from frost (see 30.1 and clause 35). If freezing occurs either during construction or shortly after completion of the work, frost may cause damage to mortar and certain masonry units if they have become saturated during construction. Additional consideration should be given to the choice of masonry units and mortar if the walling is liable to be splashed by de-icing salts from roadways or if the building is to be located in conditions of extreme exposure to weather. 22.3.2 For fired-clay masonry units, neither strength nor water absorption are reliable guides for assessing the resistance to freezing and there is no substitute for experience of performance in a particular situation. There is no test method in any British Standard for assessing frost resistance of fired-clay products, although a test being developed by the British Ceramic Research Association is referred to in BS 3921. The best evidence of ability to withstand frost damage is provided by brickwork which has been in service for some years. Where brickwork is used in situations in which it may become saturated and will be exposed to cyclic frost action, the frost resistant category (F) specified in BS 3921 should be used and if there is any doubt it is strongly recommended that the manufacturer’s advice as to the suitability of his product should be sought. 22.3.3 For calcium silicate bricks, durability and compressive strength are related, and experience shows that repeated freezing and thawing has little effect on bricks. Bricks of strength class 3 of BS 187 possess good frost resistance in most applications, but higher strength classes are recommended in very exposed situations. Calcium silicate bricks may suffer deterioration if impregnated with strong salt solutions and then subjected to intense freezing. They should thus not be used in situations where the masonry may be directly wetted by sea-water or subjected to contamination by repeated applications of road de-icing salts. 22.3.4 Precast concrete masonry units possess good frost resistance and, in general, provided that they are selected following the recommendations of this code, problems should not occur.
Where masonry remains wet, expansion and deterioration of mortar can occur as a result of chemical reaction between soluble sulphates and tri-calcium aluminate in the Portland cement in the presence of water. The reaction, forming calcium sulphoaluminate (ettringite), is accompanied by an expansion leading to cracking and crumbling of the mortar and in severe cases may lead to distortion or rotation of the masonry. The sulphates may be derived from ground waters, from the ground (including made-up fill adjacent to the masonry), from flue gases, or from fired-clay masonry units and aggregates. The degree to which soluble salts are extracted depends on the quantity of water available and the permeability of the masonry. For this reason, the greatest attention should be given to the provision of effective d.p.cs and to the exclusion of water by good design and detailing (see 21.4). Where masonry is likely to remain wet for long periods of time, e.g. in freestanding boundary walls, retaining walls, parapet walls, below d.p.c. at or near ground level, and all elevations exposed to exceptionally severe wind-driven rain, sulphation of mortar can occur and consideration should be given to the use of strong mixes or of ordinary or sulphate-resisting Portland cement in mortars used in these situations. Calcium silicate and concrete masonry units do not contain significant amounts of soluble sulphates. However, where it is intended to use concrete masonry units, expert advice should be sought, taking into account local ground conditions.
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22.5 Architectural features For aesthetic reasons, designers may sometimes include features which lead to increased local exposure of the masonry. As a result, the masonry will be more likely to become very wet or saturated, so increasing the risk of frost damage or disfiguration. In such cases it is essential to select more durable masonry units and mortar, and this may in turn govern the choice for the whole building. Examples of architectural features leading to increased local exposure are: a) recessed windows with sloping masonry at the bottom; b) flush sills; c) inadequate or non-existent overhangs at verges; d) large expanses of glazing or impermeable cladding with no effective form of construction at the base designed to shed run-off clear of the masonry beneath;
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e) areas of rendering adjoining the masonry and recessed from it without an efficient seal or other detail at the junction of the rendering and the masonry; f) vertical tile hanging, the lower edge of which has little or no projection over the walling below. There has been an increasing tendency to use cappings for masonry parapet walling. The capping may be brick-on-edge, brick-on-end, bonded brickwork or a purpose-made capping unit. Such cappings give relatively little protection to the masonry beneath, which may become saturated for up to 1 m below the capping level, depending on the water absorption of the masonry units used. It is strongly recommended that parapets and chimneys be protected by copings and d.p.cs (see 21.7). Since chimney stacks are normally exposed on all four faces and the top, they may be more liable to saturation and frost attack than other parts of the building, especially where an effective coping has not been provided at the terminal.
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Cappings of brickwork and tile creasings, even though flaunched with mortar, cannot be relied upon to keep out moisture indefinitely and require an effective d.p.c. beneath them. Where possible, a precast concrete coping in one piece, with weathered top and ample overhang, properly throated, is preferred. 22.6 Selection of masonry units and mortar for durability Table 13 gives guidance on the choice of masonry units and mortar designations most appropriate for particular situations as regards durability. At the design stage, the weather conditions at the time of building will rarely be known and indeed building may continue through more than one winter period. The recommendations given, therefore, relate to cold weather when night frost is expected but even so it is essential to protect fully masonry units, mortar and masonry under construction from saturation and freezing (see clauses 30 and 35). Reference to experience of durability in service of masonry units and mortar produced from local constituent materials in the geographical area concerned may provide valuable guidance.
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Table 13 — Durability of masonry in finished construction (A) Work below or near external ground level Masonry condition or situation
Quality of masonry units and appropriate mortar designations Fired-clay units
Calcium silicate Concrete bricks units
Concrete blocks
FL, FN, ML or MN Classes 3 to 7 W 15 N/mm2 A1 Low risk of in i), ii) or iii) in iii) or iv) saturation in iii) (see remarks) with or without freezing
a) of block density W 1 500 kg/m3; or b) made with dense aggregate complying with BS 882 or BS 1047; or c) having a compressive strength W 7 N/mm2; or d) most types of autoclaved aerated block (see remarks) in iii)
A2 High risk of FL, FN, ML or MN Classes 3 to 7 W 15 N/mm2 saturation in i) or ii) in ii) or iii) in ii) or iii) without freezing (see remarks)
As for A1 in ii) or iii)
A3 High risk of saturation with freezing
FL or FN in i) or ii)
Classes 3 to 7 W 20 N/mm2 in ii) in ii) or iii)
As for A1 in ii)
B1 In buildings
Damp-proof course 1 as described in BS 3921, in i)
Not suitable
Not suitable
Not suitable
B2 In external works
Damp-proof course 2 as described in BS 3921, in i)
Not suitable
Not suitable
Not suitable
Remarks
Some types of autoclaved aerated concrete block may not be suitable. The manufacturer should be consulted. If sulphate ground conditions exist, the recommendations in 22.4 should be followed Where designation iv) mortar is used it is essential to ensure that all masonry units, mortar and masonry under construction are protected fully from saturation and freezing (see clause 30 and clause 35) The masonry most vulnerable in A2 and A3 is located between 150 mm above, and 150 mm below, finished ground level. In this area masonry will become wet and may remain wet for long periods of time, particularly in winter. Where FN or MN fired-clay units are used in A2 or A3, sulphate-resisting cement should be used (see 22.4)
(B) D.p.cs
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Masonry d.p.cs can resist rising damp but will not resist water percolating downwards. If sulphate ground conditions exist, the recommendations in 22.4 should be followed. D.p.cs of fired-clay units are unlikely to be suitable for walls of other masonry units, as differential movement may occur (see 20.1)
(C) Unrendered external walls (other than chimneys, cappings, copings, parapets, sills) Masonry condition or situation
C1 Low risk of saturation C2 High risk of saturation
Quality of masonry units and appropriate mortar designations Fired-clay units
Calcium silicate Concrete bricks units
FL, FN, ML or MN Classes 2 to 7 in i), ii) or iii) in iii) or iv) (see remarks) FL or FN in i) or ii) Classes 2 to 7 (see remarks) in iii)
Remarks
Concrete blocks
W 7 N/mm2 in iii)
Any in iii) or iv) (see remarks)
W 15 N/mm2 in iii)
Any in iii)
(D) Rendered external walls (other than chimneys, cappings, copings, parapets, sills) Any in iii) or iv) Classes 2 to 7 W 7/mm2 Rendered external FN or MN in i) (see remarks) or ii) (see remarks) in iii) or iv) walls (other than in iii) chimneys, cappings, or FL or ML in i), ii) (see remarks) or iii) parapets, sills)
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(E) Internal walls and inner leaves of cavity walls Internal walls FL, FN, ML, MN, Classes 2 to 7 W 7 N/mm2 Any in iii) or iv) and inner leaves OL or ON in iii) or iv) (see remarks) in iv) of cavity walls in i), ii), iii) or iv) (see remarks) (see remarks) (see remarks)
Walls should be protected by roof overhang and other projecting features to minimize the risk of saturation. However, weathering details may not protect walls in conditions of very severe driving rain (see 21.3). Certain architectural features, e.g. brickwork below large glazed areas with flush sills, increase the risk of saturation (see 22.5). Where designation iv) mortar is used it is essential to ensure that all masonry units, mortar and masonry under construction are protected fully from saturation and freezing (see clause 30 and clause 35). Where FN fired-clay units are used in designation ii) mortar for C2, sulphate-resisting cement should be used (see 22.4). Rendered walls are usually suitable for most wind-driven rain conditions (see 21.3). Where FN or MN fired-clay units are used, sulphate-resisting cement should be used in the mortar and in the base coat of the render (see 22.4). Where designation iv) mortar is used it is essential to ensure that all masonry units, mortar and masonry under construction are protected fully from saturation and freezing (see clauses 30 and 35) Where designation iv) mortar is used it is essential to ensure that all masonry units, mortar and masonry under construction are protected fully from saturation and freezing (see clauses 30 and 35)
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Table 13 — Durability of masonry in finished construction
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Table 13 — Durability of masonry in finished construction (F) Unrendered parapets (other than cappings and copings) Masonry condition or situation
F1 Low risk of saturation, e.g. low parapets on some single-storey buildings
Quality of masonry units and appropriate mortar designations Fired-clay units
Calcium silicate Concrete bricks units
FL, FN, ML or MN Classes 3 to 7 W 20 N/mm2 in i), ii) or iii) in iii) in iii)
FL or FN in i) or ii) Classes 3 to 7 W 20 N/mm2 F2 High risk of (see remarks) in iii) saturation, in iii) e.g. where a capping only is provided for the masonry (G) Rendered parapets (other than cappings and copings) Rendered parapets FN or MN in i) Classes 3 to 7 W 7 N/mm2 (other than cappings or ii) (see remarks) in iii) in iii) and copings) or FL or ML in i), ii) or iii)
Concrete blocks
Remarks
a) of block density W 1 500 kg/m3; or b) made with dense aggregate complying with BS 882 or BS 1047; or c) having a compressive strength W 7 N/mm2; or d) most types of autoclaved aerated block (see remarks) in iii) As for F1 in ii)
Most parapets are likely to be severely exposed irrespective of the climatic exposure of the building as a whole. Copings and d.p.cs should be provided wherever possible. Some types of autoclaved aerated concrete block may not be suitable. The manufacturer should be consulted. Where FN fired-clay units are used in F2, sulphate-resisting cement should be used (see 22.4)
Any in iii)
Single-leaf walls should be rendered only on one face. All parapets should be provided with a coping. Where FN or MN fired-clay units are used, sulphate-resisting cement should be used in the mortar and in the base coat of the render (see 22.4)
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(H) Chimneys Masonry condition or situation
H1 Unrendered with low risk of saturation H2 Unrendered with high risk of saturation
H3 Rendered
Quality of masonry units and appropriate mortar designations Fired-clay units
Calcium silicate Concrete bricks units
Concrete blocks
FL, FN, ML or MN Classes 3 to 7 W 10 N/mm2 in i), ii) or iii) in iii) in iii)
Any in iii)
FL or FN in i) or ii)
a) of block density W 1 500 kg/m3; or b) made with dense aggregate complying with BS 882 or BS 1047; or c) having a compressive strength W 7 N/mm2; or d) most types of autoclaved aerated block (see remarks) in ii) Any in iii)
FL or ML in i), ii) or iii) or FN or MN in i) or ii) (I) Cappings, copings and sills Cappings, copings FL or FN in i) and sills
Classes 3 to 7 W 15 N/mm2 in iii) in iii)
Classes 3 to 7 W 7 N/mm2 in iii) in iii)
Classes 4 to 7 W 30 N/mm2 in ii) in ii)
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a) of block density W 1 500 kg/m3; or b) made with dense aggregate complying with BS 882 or BS 1047; or c) having a compressive strength W 7 N/mm2; or d) most autoclaved aerated blocks (see remarks) in ii)
Remarks
Chimney stacks are normally the most exposed masonry on any building. Due to the possibility of sulphate attack from flue gases the use of sulphate-resisting cement in the mortar and in any render is strongly recommended (see 22.4). Brickwork and tile cappings cannot be relied upon to keep out moisture indefinitely. The use of a coping is preferable. Some types of autoclaved aerated concrete block may not be suitable for use in H2. The manufacturer should be consulted.
Some autoclaved aerated concrete blocks may be unsuitable for use in I. The manufacturer should be consulted. Where cappings or copings are used for chimney terminals, the use of sulphate-resisting cement is strongly recommended (see 22.4). D.p.cs for cappings, copings and sills should be bedded in the same mortar as the masonry units.
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Table 13 — Durability of masonry in finished construction
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Table 13 — Durability of masonry in finished construction (J) Freestanding boundary and screen walls (other than cappings and copings) Masonry condition or situation
J1 With coping
J2 With capping
Quality of masonry units and appropriate mortar designations Fired-clay units
FN or MN in i) or ii) or FL or ML in i), ii) or iii) FL or FN in i) or ii) (see remarks)
Calcium silicate Concrete bricks units
Concrete blocks
Classes 3 to 7 W 15 N/mm2 in iii) in iii)
Any in iii)
Classes 3 to 7 W 20 N/mm2 in iii) in iii)
a) of block density W 1 500 kg/m3; or b) made with dense aggregate complying with BS 882 or BS 1047; or c) having a compressive strength W 7 N/mm2; (see remarks); or d) most types of autoclaved aerated block (see remarks) in ii)
Remarks
Masonry in free-standing walls is likely to be severely exposed, irrespective of climatic conditions. Such walls should be protected by a coping wherever possible and d.p.cs should be provided under the copings and at the base of the wall (see clause 21). Where FN or MN fired-clay units are used for J1 in conditions of severe driving rain (see clause 21), the use of sulphate-resisting cement is strongly recommended (see 22.4). Where designation iii) mortar is used for J2, the use of sulphate-resisting cement is strongly recommended (see 22.4). Some types of autoclaved aerated concrete block may also be unsuitable. The manufacturer should be consulted.
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(K) Earth-retaining walls (other than cappings and copings) Masonry condition or situation
Quality of masonry units and appropriate mortar designations Fired-clay units
Calcium silicate Concrete bricks units
K1 With waterproofed retaining face and coping
FL, FN, ML or MN Classes 3 to 7 W 15 N/mm2 in i) or ii) in ii) or iii) in ii)
K2 With coping or capping but no waterproofing on retaining face
FL or FN in i)
Classes 4 to 7 W 30 N/mm2 in ii) in i) or ii)
Concrete blocks
a) of block density W 1 500 kg/m3; or b) made with dense aggregate complying with BS 882 or BS 1047; or c) having a compressive strength W 7 N/mm2; or d) most types of autoclaved aerated block (see remarks) in ii) As for K1 but in i) or ii) (see remarks)
Remarks
Because of possible contamination from the ground and saturation by ground waters, in addition to subjection to severe climatic exposure, masonry in retaining walls is particularly prone to frost and sulphate attack. Careful choice of materials in relation to the methods for exclusion of water recommended in clause 21 is essential. It is strongly recommended that such walls be backfilled with free draining material. The provision of an effective coping with a d.p.c. (see clause 21) and waterproofing of the retaining face of the wall (see 22.1.3) is desirable. Where FN or MN fired-clay units are used, the use of sulphate-resisting cement may be necessary (see 22.4). Some types of autoclaved aerated concrete block are not suitable for use in K1. The manufacturer should be consulted. Most concrete blocks are not suitable for use in K2. The manufacturer should be consulted.
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Table 13 — Durability of masonry in finished construction
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Table 13 — Durability of masonry in finished construction (L) Drainage and sewerage, e.g. inspection chambers, manholes Masonry condition or situation
Quality of masonry units and appropriate mortar designations Fired-clay units
Calcium silicate Concrete bricks units
Concrete blocks
L1 Surface water
Engineering bricks, Classes 3 to 7 W 20 N/mm2 FL, FN, ML or MN in ii) and iii) in iii) (see remarks) in i)
L2 Foul drainage (continuous contact with masonry)
Engineering bricks, Class 7 in ii) W 40 N/mm2 FL, FN, ML or MN (see remarks) with cement in i) content W 350 kg/m3 in i) or ii) Engineering bricks, Classes 3 to 7 W 40 N/mm2 Not suitable FL, FN, ML or MN in ii) and iii) with cement in i) (see remarks) content W 350 kg/m3 in i) or ii)
L3 Foul drainage (occasional contact with masonry)
a) of block density W 1 500 kg/m3; or b) made with dense aggregate complying with BS 882 or BS 1047; or c) having a compressive strength W 7 N/mm2; or d) most types of autoclaved aerated block (see remarks) in ii) Not suitable
Remarks
Where FN fired-clay units are used, sulphate-resisting cement should be used. If sulphate ground conditions exist the recommendations in 22.4 should be followed. Some types of autoclaved aerated block are not suitable for use in L1. The manufacturer should be consulted. Some types of calcium silicate brick are not suitable for use in L2 or L3. The manufacturer should be consulted.
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22.7 Protection of components embedded in masonry from corrosion
Bolts, nuts, screws, etc. should be given the same protection as the components with which they are to be used and be compatible with these components, e.g. consideration should be given to the possibility of electrolytic action between dissimilar metals. 22.7.2 Reinforcement. Reinforcement for structural use should be protected as described in BS 5628-2. Reinforcement for non-structural use should be in the appropriate category given in Table 14. 22.7.3 Timber components. Where joist ends are built into external walls or the inner leaves of cavity walls, they should be treated with preservatives. For guidance, see BS 5268-5. Joists should not project into a cavity.
22.7.1 Metal anchorages, dowels and fixings. Metal components other than wall ties built into masonry should be in the appropriate category given in Table 14. (For wall ties see Table 9.) Components in contact with or embedded in an inner leaf which is damp or exposed to periodic wetting should be protected in the same way as components in contact with or embedded in an outer leaf, e.g. below d.p.c. In Severe or Very Severe exposure conditions as defined in 21.2, only category D should be used in walls of three storeys or less. Table 14 — Protection of metal components (other than wall ties) built into masonry Type of component
Situation
Category given in Table 1 (material and recommended protective measures) Three storeys or less
More than three storeys
Anchorages, bonding ties, slip brick ties and continuous support angles
All
C or D
D
Dowels and restraint straps Joist hangers Reinforcement for non-structural use
Internal walls
A,B,C,D
A,B,C,D
In contact with or embedded in inner leaf
A,B,C,D
A,B,C,D
In contact with or embedded in outer leaf or single leaf walls
C or D
D
Lintels
All
As specified in BS 5977-2 for the appropriate type of lintel i.e. installed with or without d.p.c.
Not normally applicable. If used, special precautions may be necessary
Cavity trays
All
As specified in BS 5977-2 for lintels installed without d.p.c.
As specified in BS 5977-2 for lintels installed without d.p.c.
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BS 5628-3:1985
23 Selection of mortars
Before deciding upon the mortar, the designer should pay particular attention to local practice and 23.1 General to any mixes that have been developed to deal with The designer should carefully select the mortar special conditions. Where mortars are to be specified designation and type by reference to structural by strength or where special category construction requirements and taking into account the type of control is to be used, the proportions should be masonry unit, type of construction, position in the determined from tests (see Appendix A of building, degree of exposure (see clause 21) and the BS 5628-1:1978). possibility of early exposure to frost (see clause 22), In practice the designer has the following three together with the general properties of mortar given options. in Table 15 and 23.2. a) Specify designation and type of mortar and The mortars given in Table 15 have been selected to leave contractor free to batch mix to obtain provide the most suitable mortar that will be readily adequate workability. workable to allow the bricklayer or blocklayer to b) Specify actual mix proportions to be used for a produce satisfactory work at an economic rate, be particular sand or provide sufficient guidance on sufficiently durable and be able to assist in the grading of sand to enable the contractor to accommodating the strains arising from minor determine where, within the range, the sand movements within the wall. Where a mortar should be proportioned. Not all sands complying designation richer than the minimum designation with BS 1200 will be suitable for conditions of recommended for durability in Table 13 is required Severe or Very Severe exposure or where flexural for structural reasons, careful consideration should strength (adhesion) is critical, owing to high fines be given to the accommodation of movement content and/or particle distribution. In such (see clause 20). cases, consideration should be given to using The range of volume proportions given in Table 15 is sands having a particle size distribution towards to allow for the effect of the differences in sand the coarser end of the BS 1200 grading envelope. grading upon the properties of the mortar. Such sands may be found amongst those Proportioning by mass will produce more consistent complying with grade M of BS 882. mortars than volume proportioning, provided that c) Specify the lowest mix proportions for each the variation in bulk densities of the materials is type and designation, e.g. specify 1 : 1 : 5 for checked on site constantly. designation iii) cement : lime : sand. Table 15 — Mortar mixes Mortar designation
Type of mortar (see note 2) Cement : lime : sand (see note 3)
Proportions by volume (see note 4) Increasing strength (see note 1) and improving durability
Increasing ability to accommodate movements due to temperature and moisture changes
i) ii) iii) iv) v)
Direction of change in properties is shown by the arrows
1 : 0 to ! : 3 1 : " :4 to 4" 1 : 1 : 5 to 6 1 : 2 : 8 to 9 1 : 3 : 10 to 12
Air-entrained mixes (see note 5) Masonry cement : sand (see note 3)
Cement : sand with plasticizer (see note 3)
Proportions by volume
Proportions by volume
1 : 2" to 3" 1 : 4 to 5 1 : 5" to 6" 1 : 6" to 7
1 : 3 to 4 1 : 5 to 6 1 : 7 to 8 1:8
Increasing resistance to frost attack during construction Improvement in adhesion and consequent resistance to rain penetration
NOTE 1 Where mortar of a given compressive strength is required by the designer, the mix proportions should be determined from tests following the recommendations of Appendix A of BS 5628-1:1978. NOTE 2 The different types of mortar that comprise any one designation are approximately equivalent in compressive strength and do not generally differ greatly in their other properties. Some general differences between types of mortar are indicated by the arrows at the bottom of the table, but these differences can be reduced (see 23.2.1). NOTE 3 The range of sand contents is to allow for the effects of the differences in grading upon the properties of the mortar. In general, the lower proportion of sand applies to grade G of BS 1200 whilst the higher proportion applies to grade S of BS 1200. NOTE 4 The proportions are based on dry hydrated lime. The proportion of lime by volume may be increased by up to 50 % (V/V) in order to obtain workability. NOTE 5 At the discretion of the designer, air entraining admixtures may be added to lime : sand mixes to improve their early frost resistance. (Ready mixed lime : sand mixes may contain such admixtures.)
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23.2 Types of mortar 23.2.1 General. About one volume of binder is needed for three volumes of sand to give a workable mix but cement mortar of this kind is stronger than is necessary for most uses. For weaker mortars, lime or plasticizers are needed to maintain workability. Cement : lime : sand mortars give a stronger bond than can be obtained with air-entrained mortars of similar compressive strength. This better bond is likely to result in greater resistance to rain penetration and improved flexural strength. However, the air-entrained mortars are generally more resistant to damage by freezing, particularly at early ages (see 35.3). These general differences between the properties of types of mortar may be reduced by admixtures or special treatments. For example, the adhesion of air-entrained mortars to dry absorbent units can be considerably improved by water-retaining admixtures. Air-entrainment of cement : lime : sand mortars will improve their resistance to damage by freezing at an early age. However, the use of such admixtures should be at the discretion of the designer. 23.2.2 Cement mortar. Adequate strength in the fully hardened mortar, combined with a rapid development of strength in the early stages, is most conveniently attained by the use of Portland cement, but it is not practicable to adjust the strength simply by varying the ratio of cement to sand, because lean mixes of cement and sand are harsh and unworkable. 23.2.3 Cement : lime : sand mortar. Mortars made with appropriate proportions of Portland cement, including sulphate-resisting Portland cement and lime, take advantage of the useful properties of each. Cement : lime : sand mortars are designed on the principle that part of the cement is replaced by an equal volume of lime so that the binder-paste still fills the voids in the sand. In this way good working qualities, water retention, adhesion and early strength can be secured without the mature strength being too high. The lime used should be non-hydraulic (high calcium or magnesian) or semi-hydraulic. 23.2.4 Masonry cement mortar. The good working properties of mortar mixes made with masonry cement are derived from the plasticizing effects of the fine filler and the entrained air. 23.2.5 Air-entrained (plasticized) mortar. Mortar plasticizers which entrain air in the mix provide an alternative to lime for imparting good working qualities to lean cement : sand mixes. In effect, the air bubbles serve to increase the volume of the binder paste, filling the voids in the sand, and this correspondingly improves the working qualities.
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23.2.6 Ready-to-use retarded cement : lime : sand mortar and cement : sand mortar. Ready-to-use retarded cement : lime : sand mortars and cement : sand mortars may be considered for use where consistent non-structural properties, e.g. colour, are particularly required. For use in structural masonry, see 15.2 of BS 5628-1:1978. 23.2.7 Lime : sand mortar. Lime : sand mortar should be in accordance with clause 13 of BS 6270-1:1982. 23.3 Admixtures intended to resist frost damage to mortar Although when frost conditions are anticipated there would be some advantage in accelerating the setting of the mortar, in practice no suitable admixtures are known that are free from other undesirable effects. In particular, calcium chloride or admixtures based on this salt may lead to subsequent dampness or corrosion of embedded metals, including wall ties, and therefore should never be used. There is little experience of the successful use of any admixture intended to provide frost protection by depressing the freezing point of the mixing water. Some substances that might be contemplated for this purpose, e.g. ethylene glycol, are known to adversely affect the hydration of the cement.
24 Fire resistance Masonry walls should be designed to have a fire resistance appropriate to their use. NOTE The fire resistance is taken to be the time from the start of the tests laid down in BS 476-8 until failure first occurs under any one of the listed criteria, i.e. stability, integrity and thermal insulation. This time ranges from 30 min to 6 h and is a property of the complete element of structure.
Table 16 gives notional fire resistances of walls for various types of construction. Other forms of construction may be used, provided evidence of satisfactory performance in use, based on the results of standard fire resistance tests, is produced. If the required fire resistance of a loadbearing cavity wall with a thickness taken from Table 16 is more than 2 h, the imposed load should be shared by both leaves; otherwise, if the load is carried by the exposed leaf only, the minimum thickness of the exposed leaf should be that given for loadbearing single-leaf walls. For panel walls required to provide fire resistance where edge isolation is necessary, special consideration should be given to the edge details. Where movement joints or edge clearances are required for walls designed to resist fire, they should be filled with a non-combustible material, such as mineral fibre, which still allows the movement joint to function. © BSI 11-1999
BS 5628-3:1985
Table 16 — Notional fire resistance of walls (see note 1) (A) Loadbearing single-leaf walls Material
Masonry unit
Brick Fired, brick-earth clay or shale
Type
Finish (see note 2)
Solid None (see note 4)
Minimum thickness of masonry (in mm) (see note 3) for notional period of fire resistance of 6h
4h
3h
2h
90 min
60 min
30 min
200
170
170
100
100
90
90 (see note 5)
170
100
100
90
90
90
90 (see note 5)
None — or SC/SG
200
200
170
170
170
100
VG
170
170
170
100
100
90
Not less SC/SG — than 50 % VG — solid
—
—
215
215
215
215
215
215
215
215
215
215
Not less None — than 40 % or solid SC/SG
—
—
—
—
215
215
Two cells SC/SG — Block (outer-web (see note 6) not less than not less 13 mm thick) than 50 % solid
—
—
100
100
100
100
Three cells SC/SG — (see note 6) not less than 60 % solid
150
150
150
150
150
150
Solid None (see note 4) VG
200
190
190
100
100
90
90
200
100
100
90
90
90
90
Solid
None
150
150
140
100
100
90
90
VG
150
100
100
90
90
90
90
—
—
—
100
100
100
90
None — or SC/SG
—
—
100
100
90
90
VG
100
100
90
90
90
90
Other, SC/SG — e.g. hollow VG —
—
—
—
—
—
190
—
—
200
200
190
190
Solid
VG Not less than 75 % solid, e.g. perforated
Concrete or Brick calcium silicate Concrete, class 1 aggregate (see note 7)
Block
Concrete, class 2 aggregate (see note 7)
Block
Other, None e.g. hollow
Block Aerated concrete, density 480 kg/m3 to 1 200 kg/m3
Solid
200
—
None
215
180
140
100
100
90
90
VG
180
150
100
100
90
90
90
See notes at end of table.
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Table 16 — Notional fire resistance of walls (see note 1) (B) Non-loadbearing single-leaf walls Material
Masonry unit
Brick Fired brick-earth, clay or shale
Type
Finish see note 2)
Minimum thickness of masonry (in mm) (see note 3) for notional period of fire resistance of 6h
4h
3h
2h
90 min
60 min
30 min
Solid None (see note 4) VG
200
170
170
100
90
75
75
100
100
90
90
90
75
75
Not less None than 75 % VG solid, e.g. perforated
200
200
170
170
100
100
75
170
170
100
100
90
75
75
Not less SC/SG — than 50 % solid VG —
—
—
215
215
215 215 (see note 8) (see note 8)
215
215
215
215
215 215 (see note 8) (see note 8)
Not less None than 40 % solid
—
—
—
—
—
215
215
SC/SG — One cell Block (outer-web (see note 6) not less than not less 13 mm thick) than 50 % solid
—
—
—
—
100
75
SC/SG — One cell (see note 6) not less than 30 % solid
—
—
—
—
150
150
Two cells SC/SG — (see note 6) not less than 70 % solid
—
—
100
100
100
75
Two cells SC/SG — (see note 6) not less than 45 % solid
—
—
225
225
150
150
Two cells SC/SG — (see note 6) not less than 50 % solid
—
—
—
—
—
Three cells SC/SG — (see note 6) not less than 70 % solid
150
150
150
150
150
150
Solid None (see note 4) VG
200
170
170
100
90
75
75
100
100
90
90
90
75
75
Concrete or Brick calcium silicate
75
See notes at end of table.
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Table 16 — Notional fire resistance of walls (see note 1) (B) Non-loadbearing single-leaf walls Material
Concrete, class 1 aggregate (see note 7)
Concrete, class 2 aggregate (see note 7)
Masonry unit
Block
Type
Solid
Finish (see note 2)
None
Block Aerated concrete, density 480 kg/m3 to 1 200 kg/m3
6h
4h
3h
2h
90 min
60 min
30 min
150
140
125
75
75
75
50
SC/SG 150
100
90
75
75
75
50
100
75
75
75
63
50
50
Other, None 225 e.g. hollow SC/SG 150
150
140
100
90
90
75
140
140
100
75
75
75
VG
Block
Minimum thickness of masonry (in mm) (see note 3) for notional period of fire resistance of
VG
150
100
90
75
75
63
63
None
200
150
140
100
90
75
50
SC/SG 150
140
100
90
90
75
50
VG
125
100
90
75
75
75
50
Other, None 215 e.g. hollow SC/SG 150
150
140
140
125
125
90
140
140
140
125
125
90
Solid
VG
150
125
125
100
90
90
75
None
150
100
75
63
63
50
50
Solid None (see note 4)
100
100
100
100 100 (see (see note 9) note 9)
90
90
150
150
100
100
100
100
Not less SC/SG — than 50 % solid
—
—
100
100
100
100
Solid
100
100
100
100 100 (see note 9)
90
90
Other, None e.g. hollow
—
100
100
100
100
100
90
Solid
—
—
—
100
100
90
90
Solid
(C) Load-bearing cavity walls Brick Fired brick-earth, clay or shale, concrete or calcium silicate
SC/SG — Not less Block Fired brick-earth, (outer-web than 70 % solid, e.g. clay or shale not less 13 mm thick) perforated
Concrete, class 1 aggregate (see note 7)
Block
Concrete, class 2 aggregate (see note 7)
Block
None
None
See notes at end of table.
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Table 16 — Notional fire resistance of walls (see note 1) (C) Load-bearing cavity walls Material
Masonry unit
Type
Finish (see note 2)
Block Solid None Aerated concrete, density 480 kg/m3 to 1 200 kg/m3 (D) Non-loadbearing cavity walls Brick Solid None Fired (see note 4) brick-earth, clay or shale, Not less None concrete or than 50 % calcium solid silicate Fired SC/SG Not less Block brick-earth, (outer-web than 70 % clay or shale not less than solid, e.g. 13 mm thick) perforated Not less SC/SG than 50 % solid Block Solid None Concrete, class 1 Other, None aggregate e.g. hollow (see note 7) Block Solid None Concrete, class 2 aggregate (see note 7) Block Solid None Aerated concrete, density 480 kg/m3 to 1 200 kg/m3
Minimum thickness of masonry (in mm) (see note 3) for notional period of fire resistance of 6h
4h
3h
2h
90 min
60 min
30 min
150
150
140
100
100
90
90
100
75
75
75
75
75
75
—
100
90
90
90
90
90
100
100
100
100
100
100
100
—
100
100
100
100
100
100
90 100
75 75
75 75
75 75
75 75
75 75
75 50
90
75
75
75
75
75
50
90
75
75
63
63
50
50
NOTE 1 Non-loadbearing walls are assumed to carry no load other than their own weight and edge restraint. Loadbearing walls may carry any load up to that which produces the maximum permissible design stresses. Interpolation between Table 16(A) and Table 16(B) or between Table 16(C) and Table 16(D) is not permitted. NOTE 2 The finish should be not less than 13 mm plaster or rendering on each face of a single-leaf wall and on the exposed faces of a cavity wall. SC/SG is sand : cement or sand : gypsum (with or without lime). Plasterboard of an equivalent thickness may be substituted for fire resistance periods up to 2 h. VG is vermiculite : gypsum plaster (1" : 1 to 2 : 1 by volume). Perlite may be substituted for vermiculite for fired-clay bricks and other materials with similar surfaces. NOTE 3 The thickness represents either the work size of the unit, or, where applicable for solid walls, the sum of the work sizes of two units together with the work size of the joint between them. NOTE 4 A solid brick is a brick without frogs or with frogs up to 20 % of its volume, but with no through holes or perforations. NOTE 5 The minimum thickness given is suitable for 75 mm brick-on-edge construction with a completely solid unit with plane faces. NOTE 6 The number of cells is that in any cross section through the wall thickness. NOTE 7 Class 1 aggregates for concrete blocks include limestone, air-cooled blast-furnace slag, foamed or expanded slag, crushed brick, well-burnt clinker, expanded clay or shale, sintered pulverized-fuel ash and pumice. Class 2 aggregates for concrete blocks include all gravels and crushed natural stone, except limestone. NOTE 8 These thicknesses may be reduced to 100 mm for walls built with cellular bricks. NOTE 9 These thicknesses may be reduced to 90 mm if the load is distributed over both leaves.
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25 Thermal properties
If a masonry construction is finished internally with a thermally insulating lining, this will modify the response to internal temperature changes. In summer, the adverse effects of solar gain are reduced by the use of masonry external walls.
25.1 General
25.5 Cold bridges
The thermal properties of a wall should strike a balance between heat loss and gain, thermal capacity and energy consumption. Internal wall surface temperatures should be considered in relation to user comfort and the risk of condensation. The loss or gain of heat through a wall depends on the temperature difference between the air on both sides of the wall, the thermal resistance of the materials, their surfaces and the spaces between them.
Where the insulant is not continued across the entire construction for structural or other reasons, the thermal resistance is reduced. This is characterized by a drop in the surface temperature of the wall in the region of the “cold bridge”. This may cause pattern staining and surface condensation.
Consideration should also be given to non-combustible cover strips fixed to both faces of the wall on one side of the joint.
25.2 U-values For the purposes of comparing alternative constructions or checking compliance with legislation, thermal conductivity figures for use in calculating standardized U-values are given in the CIBS Guide Section A3 “Thermal properties of building structures”6) 1980. It should be noted that large discrepancies may occur between calculated and achieved U-values, due mainly to the effect on thermal resistance of moisture content, wind speed and surface roughness. The CIBS Guide allows for this and recommends adjusting U-values to suit the particular form of construction to be used on specific sites. 25.3 Thermal insulation The insulation value of masonry external walls may be improved by adding insulants of high thermal resistance. These may be positioned externally, internally or within the cavity. Reference should be made to appropriate British Standards concerning methods of application and suitability for particular exposure conditions (see 21.3.2.8). The designer should ensure that the construction selected is also in accordance with other recommendations of this code. 25.4 Thermal capacity When considering space heating, buildings may be categorized as low thermal capacity (lightweight) or high thermal capacity (heavyweight), according to the characteristics they display to the interior. Lightweight structures respond quickly to changes in external and internal conditions. Heavyweight structures dampen the effects of heat gains and therefore heat up and cool down more slowly.
6) Available
25.6 Condensation Condensation will occur on a surface when its temperature is below the dewpoint of the air in contact with it. The internal surface temperature of constructions which avoid cold bridges and have some thermal mass on the inside of the insulation will often remain high enough to prevent surface condensation. Cold non-absorbent surfaces are particularly prone to condensation. Absorbent materials can disguise condensation and allow it to evaporate later. If, however, persistent condensation occurs, there is a risk that decorations will be damaged by mould growth. For further information, see BS 5250. Interstitial condensation may form within the layers of a construction when the temperature of the structure falls below the temperature at which water vapour will condense as it passes through the wall. Problems are unlikely to arise in cavity walls where the layers of the construction offer progressively less vapour resistance towards the external face.
26 Sound absorption and noise reduction 26.1 Sound absorption Sound absorption should not be confused with sound insulation. Sound absorbent materials reflect only a small proportion of the incident noise falling on their surface. In this way the level of noise within adjacent spaces or enclosures may be reduced, but this does not influence greatly the sound transmitted through to another area or enclosure. Sound absorbent materials are not necessarily good sound insulating materials.
from the Chartered Institution of Building Services, Delta House, 222 Balham High Road, London SW12 9BS.
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26.2 Sound insulation and resistance to sound transmission 26.2.1 General principles. Sound is transmitted from its source to adjacent spaces or enclosures by a multitude of routes involving airborne and structure-borne transmission. Structure-borne sound can originate from impact on a surface or from airborne sound impinging on the surface of the structure; however, when designing walls, the origin is generally assumed to be airborne rather than impact sound. Sound generated in the air in one room radiates to the surfaces of the enclosing structure and is transmitted through the structural elements. separating walls, and flanking walls and floors to an adjacent room, where the sound is finally transmitted through the air to the ear. The sound insulation of single-leaf masonry walls is largely related to their mass per unit area, provided that there are no direct air paths through the wall. Even very small air paths such as cracks and poorly filled cross joints in unplastered masonry or masonry finished with a dry lining, will greatly reduce the sound insulation. The sound insulation of a cavity wall is related to its mass per unit area, the width of the cavity and the rigidity and spacing of the wall ties. A cavity wall of nominal cavity width 50 mm and with leaves connected by wire butterfly ties as recommended in 19.5 may be expected to have a resistance to sound transmission similar to that of a solid masonry wall of the same surface mass. If more rigid ties or a greater number of ties per square metre are used, the sound insulation of the wall will decrease. Conversely, if the ties are omitted, the sound insulation will improve. In addition, the wider the cavity, the better the sound insulation. Of equal importance is the reduction of flanking transmission. Direct air paths around the separating wall have to be avoided. Window reveals have to be sealed to prevent direct transmission with the cavity. Care has to be taken to avoid air paths through floors which are continuous through the separating wall. Unplastered walls in attics or roof spaces should be well built with all bed joints and perpend joints filled. The designer should consider the detailed recommendations given in 26.2.2 when seeking to achieve satisfactory sound insulation. 26.2.2 Construction details 26.2.2.1 Separating walls. The minimum thickness of a separating wall required for sound insulation should always be maintained, particularly where chases, recesses, chimney flues, electrical sockets, etc. are to be built into a wall.
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Where joists span perpendicular to the separating wall, they should be supported on joist hangers and not built into the wall. Hollow cored concrete floor units supported on separating walls should have their voids filled at the bearings. The surface of a wall formed from materials with coarse interconnecting pores should be sealed, even when dry lined. In addition, surfaces should be sealed below suspended floors within the depth of the floor construction and in the roof space. Plastered resilient materials, e.g. polystyrene board, should not be used for sound insulation without expert advice. Connections between leaves of party walls should be kept to the minimum consistent with structural stability. If butterfly ties are not permissible, it is better to use a single-leaf wall. 26.2.2.2 External flanking walls. To minimize the risk of direct sound transmission around a separating wall and to provide stiffness to the separating wall, full storey height window or door openings should not be placed adjacent to the separating wall. Adjoining openings should be separated across the party wall or the party wall should be continued beyond the flanking wall. Reveals of openings should be sealed to reduce transmission along the cavity of the external wall. Fibrous materials used for fire stops cannot be relied upon to provide an adequate acoustic barrier in the flanking path. Masonry-separating walls should be preferably bonded to one leaf of the external masonry walls, rather than tied across a butt joint. Plastered resilient materials, e.g. polystyrene board, on the internal face should not be used for sound insulation without expert advice.
27 Masonry bonds and other constructional details 27.1 Masonry bonds 27.1.1 General. The horizontal distance between cross joints in successive masonry courses should normally be not less than one-quarter of the length of the units but in no case less than 50 mm for bricks or 75 mm for blocks. Those patterns which depart from the principle of having adequate distance between the cross joints in adjacent courses, particularly stack bond, should be used only where experience or experimental data indicate that they are satisfactory for the particular construction.
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The overall dimensions of walls and the positions and sizes of openings and piers should be chosen bearing in mind the dimensions of the type of unit to be used and the dimensions of the special units available, so that cutting of the units will be kept to a minimum and irregular or broken bond will be avoided. Flue blocks, where built into a wall, should be bonded. The choice of bond may be affected by the need to include reinforcement. The types of masonry bonds and joint finishes that are commonly used are detailed in Appendix B. 27.1.2 Brickwork masonry bonds. The masonry bonds described in B.1 are commonly used in brickwork. Other ornamental bonds, designed for appearance only, may be derived from these principal bonds. Stretcher bond, which consists of stretchers only in each course, is normally used for leaves one-half brick thick whether in solid or cavity walls; other bonds should not be used for such cavity walls unless purpose-made bats are available. The lap is normally half the length of the brick but the distance may be reduced to not less than 50 mm, as, for example, in short lengths of partition walls to accommodate block bonding of return and intersecting walls made of thin blocks. Sleeper walls and non-loadbearing screen walls may be built using honeycombed construction provided the lap between courses is at least one-quarter the length of the brick. Quetta or Rat-trap bonds may be used in reinforced brick-work, because these bonds leave voids for the vertical reinforcement. Rat-trap bond is sometimes used for garden walls. As the bricks are edge bedded, leaving voids in the thickness of the wall, such walls are economical in material; however, they lack the strength of a single-leaf wall of the same overall thickness. 27.1.3 Blockwork masonry bonds. Because of the wide range of available shapes and sizes of blocks, a great variety of bonding patterns for facing blockwork is possible. The general principles of bonding given in 27.1.1 should be observed. The masonry bonds described in B.2 are commonly used in blockwork. Hollow blockwork may be suited to the incorporation of reinforcement within the voids of the units, which are filled with concrete. Where quoin or reveal blocks are used, alternate short and long blocks should be used in successive courses to ensure that the bond within the wall is retained.
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Shell bedding for solid and cellular blocks may be used only by permission of the designer, since it affects the strength of the finished wall. 27.2 Architectural features 27.2.1 Architectural features such as plinths, string courses and cornices may be formed of bricks, blocks or other suitable materials. Their design may involve considerations of stability, resistance to abrasion, moisture penetration (see 21.3.1 and 21.3.2.7) and durability (see 22.5), particularly where dissimilar materials are associated. Wherever possible, all features should be designed to fit with the masonry in length, height or thickness. 27.2.2 Features which project from the main plane of the wall should have their upper surfaces protected by flashings or weatherings from downward penetration of water. In modern cavity wall construction, projecting features cannot readily be secured in the wall by weight above as in older solid walls. It may therefore be necessary to hold them in place by other means, such as a reinforced concrete, reinforced masonry or steelwork core. 27.2.3 Unless bricks are selected for size, their variation in length will usually preclude the building of one brick single-leaf bonded walls having a fair face on both sides, but this can readily be achieved by using double-leaf (collar-jointed) walls instead. 27.2.4 The facing of external walls of common bricks by veneering materials requires careful consideration of their weathering and jointing characteristics. If absorbent, the veneer will add to the capacity of the wall to act as an overcoat but if the veneer is impermeable, the success of jointing in resisting penetration will become critical. If water gets behind such veneers and cannot readily escape it may cause disruption by sulphation of the mortar of the backing material or by crystallization of soluble salts. 27.2.5 Sometimes a separate leaf of brickwork of an ornamental leaf is added to a common brick wall to improve the appearance. The ornamental leaf should be adequately fixed to the parent wall, using metal ties, and due consideration should be given to stability. The parent wall should be regarded as carrying the load independently of the ornamental leaf, i.e. as a veneered wall.
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27.3 Brick and block slips
27.4 Pistol bricks
The practice has grown up of masking the edges of concrete floors or beams with courses of brick or block slips to match the facing masonry. However, lack of appreciation of the shrinkage and creep of a concrete frame, insufficient provision for thermal movement, inaccuracy of construction and lack of care in the preparation of the surfaces and choice of mortars has given rise to problems, with the slips failing in adhesion and falling from the face of the building. Where the use of slips is unavoidable, designers should pay attention to the tolerances on the materials and components to ensure correct alignment of the concrete face or nib, both horizontally and vertically, with the floors above and below. Reference may be made to BS 5606 which quotes characteristic accuracies for various materials and components. It is important also that the wall above does not overhang its support by more than one-third its width, e.g. 34 mm for a 100 mm wide leaf. The accurate positioning of the face of concrete in relation to the eventual finished face of the masonry is critical and needs close attention at all stages of design and construction. The method of fixing slips using adhesives is described in 32.12. Where more than two courses are to be fixed, a mechanical method of tying back slips, such as the one shown in Figure 13(a), should always be used to supplement the adhesives. Where fired-clay brick slips are bonded to the nib or toes of a concrete slab or beam, arrangements should be made to minimize horizontal and vertical stresses acting on the courses of slips (see 20.2.4). Bituminous paint should never be applied to concrete surfaces, as this would severely affect the adhesion between the concrete and the slips. The design should ensure that there is enough cover to reinforcement to allow for removal of laitance before fixing the slips.
The pistol brick may be used as an alternative to brick slips to mask the toes of reinforced boot lintels or beams. Unlike brick slips, its use is limited to the vertical or “soldier” arrangement and, in certain cases, this directional restriction may not be architecturally acceptable. However, it may not require adhesive fixing systems and permits the application of damp-proof coatings to the concrete surfaces when necessary. Special corner units may be supplied by some manufacturers. Generally a “barrel” thickness of 20 mm may be achieved with most types of facing bricks but it is important that over-run of the horizontal cut be avoided, as this will weaken the “barrel” at what is already its weakest point. When the bottom of the “barrel” rests on brickwork below, a flexible compressible horizontal joint as recommended for bricks slips in 20.2.4 should be provided for the full thickness of the “barrel” and its vertical backing joint. Figure 13(b) shows the essential dimensional requirements when using pistol bricks.
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27.5 Cut blocks Concrete blocks similar to pistol bricks may be used as an alternative to block slips to match facing concrete blockwork. An alternative method for masking the concrete slab or beam is the use of cut hollow blocks [see Figure 13(c)]. The cut block is cast into the slab or beam and acts as permanent shuttering whilst the concrete is being laid. It is important to ensure that the cut blocks are supported adequately on the formwork whilst the concrete is being placed.
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Figure 13 — Matching facing masonry
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Figure 13 — Matching facing masonry (continued)
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Figure 13 — Matching facing masonry (continued)
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27.6 Brick arches The traditional masonry arch, which can have many shapes, e.g. segmental, parabolic, semicircular or elliptical, is a curved assembly of voussoirs solidly buttressed at each end and proportioned so that the line of resistance to the loads falls within the middle third of the depth of the arch ring, so avoiding the development of tension at the intrados or extrados. The sides of each voussoir are determined by lines radiating from the arch centre or centres so that they are normal to the curve of the arch and thus are approximately perpendicular in minor arches to the internal line of thrust (see Figure 14). In brick masonry, the wedge shaped voussoirs, if of hard material, have to be specially made. Alternatively, if of soft bricks known as rubbers, they may be formed on site, either method resulting in gauged arches. These methods may still be demanded for restoration work (see BS 6270-1) but in modern practice normal bricks are used and the wedge shape is achieved by varying the thickness of mortar joint from intrados to extrados. Arches built this way were known previously as “rough arches” and were used as backing to gauged arches, but today they are used for facing work. For uniform loads, a parabolic shape is ideal because the line of thrust coincides with the centre line of the arch ring and eliminates bending and tension. In practice, masonry arches are built as segments of circles and a parabola is approximated when the rise of the arch equals one-eighth of the span. The difficulties of determining the actual loads acting on arched openings formed within brick masonry walls means that accurate structural design is unlikely to be achieved. Usually minor arches of segmental, parabolic or semicircular form and up to, for example, 2 m span, can be proportioned empirically, provided care is taken to ensure that there is an adequate amount of masonry over the arch ring and between it and any line of floor loads and also that adequate resistance is provided at the abutments
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The latter is more important in the uppermost storeys of loadbearing walls or where arched brickwork openings are provided in any storey height of a framed structure where the brickwork is not self-supporting. Arch construction is less suitable for the external skins of cavity walls than for solid walling of greater thickness because of the added complications of damp-proofing the junctions between inner and outer skin. The normal cavity tray (see 21.5.5) cannot readily be sloped outward and simultaneously curved to follow the outer skin unless it is in very malleable material, such as lead. 27.7 Jointing and pointing Jointing is preferable to pointing because it leaves the bedding mortar undisturbed. The mortar used for pointing should have mix proportions similar to those used in the bedding mortar. Types of finish for jointing and pointing of work are described in B.3. These should be carefully chosen in relation to colour, texture, form and durability of the units used and the conditions of exposure. Tooling of the joints to compact the mortar helps to improve the durability of the mortar and the rain-shedding capacity of the wall. Recessed joints should not be used where there is a danger of excessive wetting which may lead to damage by frost action or rain penetration. The depth of the recess should be related to the distance of any perforation of cavity from the exposed face of the unit.
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Figure 14 — Brick arches
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27.8 Corbelling
27.10 Ducts across cavities of cavity walls
Where courses are corbelled out one above the other, the extent of corbelling should not exceed that shown in Figure 15, unless the work is otherwise supported or reinforced.
Where ducts are used to ventilate a building, or bridge or close the cavity of a cavity wall, they should be designed to prevent water penetrating the inner leaf of the wall. Such ducts should, where possible, slope away from the inner leaf of the wall and be protected by a stepped d.p.c. Both ends of the duct should be protected from rubbish and vermin by an airbrick, grating or mesh such that a 10 mm diameter sphere cannot pass through.
27.9 Provision for services and fittings In deciding upon the type and thickness of the masonry unit to be used, consideration should be given to the suitability for accommodating services and for the fixing of fittings. Services may be run through ducts or on the surface of the masonry in chases. Preferably chases and sleeves should be provided during the erection of the work.
Figure 15 — Sizes of corbels
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Section 4. Workmanship 28 Setting out
29 Scaffolding
28.1 General
All scaffolding should be erected and maintained in accordance with BS 5973 or BS 5974. Putlog holes should be filled with an appropriate mortar or bat as the scaffold is demounted. Lack of care in removal of putlog scaffolding can result in cracking of horizontal mortar joints and may impair the stability of the wall. Use of independent scaffolding minimizes the risk of damage to walls.
This clause gives general guidance on setting out brick and block masonry. For more detailed information on the control of accuracy in setting out, see BS 5606. 28.2 Horizontal setting out The building should be located with reference to the dimensioned setting out drawing, which may be on a grid system, and to agreed datums and building lines. Horizontal dimensions should be set out using a steel tape or rule. Angles should be determined by optical instruments or by triangulation or by accurately constructed builders squares. It is essential that large or intricate buildings be set out using an optical instrument. The corners of the building should be located by nails or by saw-cuts in pegs driven firmly into the ground and the accuracy of the pegs checked by triangulation. Profiles, i.e. boards which are securely fixed to pegs driven into the ground and upon which the width of foundations, thickness of walls and the projection of offsets may be clearly marked by saw-cuts or nails, should then be set up in line with peg marks but further away from the corners so as to allow their use during preliminary building operations whilst remaining undisturbed. Intermediate profiles may then be established for setting out party walls and partitions. Where the shape of the wall does not permit the use of profiles, e.g. curved walls, accurately formed templates for the whole or part of the shape may be used. Curved work may be set out by theodolite; this is preferable on large radius work. Where a number of openings of similar width are to be formed, a rod cut to the required size may be used to check the width of openings as the work rises. To be of use, rod and templates have to be clearly marked. 28.3 Vertical setting out A levelling instrument and staff should be used to establish a site datum in relation to the reference level shown on the setting out drawing. The site datum should be fixed at some convenient height, preferably ground floor level, and pegs should be established indicating the datum level near each quoin; the pegs should be protected (backed up) with concrete. Where long straight length of walling occur, it may be useful to establish intermediate levels. If it is inconvenient to use pegs, brick or block piers should be used to mark the datum level. Storey or gauge rods setting out the heights in relation to the site datum should be prepared. Saw cuts in the storey rod should mark the top of each course of units, the heights of window and door openings and of other relevant features.
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30 Storage on site 30.1 General Consignments of materials should be placed so that they will normally be used in order of delivery and so as to permit the inspection and sampling of individual consignments. All materials should be inspected both when delivered to site and immediately before use, to check whether they have been subject to deterioration or damage. 30.2 Masonry units Masonry units should be unloaded by machine or by hand on to a dry and reasonably level area or scaffold. It is important that they should be carefully stacked to avoid damage and to ensure stability, and should be protected from rain and snow. For concrete and calcium silicate masonry units, it is desirable that provision is made for the free circulation of air within the stack so that masonry units may dry out before being built into the work. Particular care should be taken with facing masonry units. Masonry units should not be stacked directly on sulphate-bearing ground, clinker or ashes because of the danger of chemical contamination through rising moisture, nor should masonry units be stacked on newly cast slabs until the slabs have attained sufficient strength. Strict precautions should be taken to ensure that stacks of material on floor slabs do not overload the structure. This is particularly important where masonry units delivered in packs are hoisted direct to areas where they are to be used. It is desirable that facing masonry units should be mixed either on site or, by agreement with the manufacturer, at the works, to avoid the effect of bands of colour in the finished work. 30.3 Cement and hydrated lime Cement and hydrated lime should be stored off the ground, kept dry and used in order of delivery. Cement or hydrated lime affected by dampness should never be used.
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30.4 Fine aggregate Fine aggregates should be stored in separate bins according to type so that they will not become contaminated, preferably in bins with a dry solid base. Variations in moisture content will affect gauging (see clause 31). For guidance on work when frosty or freezing conditions may occur, see 35.3. 30.5 Ready-to-use mortars and ready-mixed lime : sand Ready-mixed lime : sand for mortar should be stored in a clean area on a hard impervious surface and should be protected from the weather to prevent wetting, drying out or freezing. Extreme variations of moisture will affect subsequent gauging. Particular care should be taken when using coloured lime : sand mixes, which should be sheeted against rain water to safeguard them from segregation of pigment. Ready-to-use retarded cement : lime : sand and cement : sand mortars should be kept in containers, e.g. skips. The containers should be covered when not in use to protect the contents from the weather. 30.6 Flexible d.p.cs Rolls should be stored on end and on a level surface away from heat taking care that the rolls do not get distorted or squashed. Preformed cavity trays should be treated with great care and stored in an area where there is no danger of items being placed on top of them. Manufacturers’ instructions should be read and carefully followed.
31 Batching, mixing and use of mortars 31.1 General The general recommendations on mix proportions given in Table 15 and Table 17 relate to normal site control where strength requirements are not specified. Where the mortar is specified by strength or where special category construction control is required by the designer, reference should be made to BS 5628-1. Mortar made on site should preferably be mixed by machine but for small quantities hand mixing may be used and should be carried out on a clean watertight platform. The machine and platform should be cleaned before use, when changing mixes, particularly with coloured mortars and immediately after mixing is completed for the shift.
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Details of the preparation of lime putty and lime : sand mixes (coarse stuff) are given in BS 6270-1; however, it is now common practice where lime is used in a mortar for it to be either added as a dry constituent during mixing or proportioned with sand and delivered to the site as ready-mixed lime : sand for mortar (see 6.6). Admixtures added on site should be used only with the permission of the designer. Guidance on batching, mixing and use of ready-to-use building mortars is given in Appendix A of BS 4721:1981. 31.2 Batching The materials for mortar should be accurately measured. When mixing by volume, a gauge box, bucket or similar standard container should be used to measure the materials. Gauging by shovels cannot be relied upon to give consistent results. The volume of each gauge box or container should be such that a whole number of volumes of each material is required for each batch of mortar. It is essential that all gauge boxes or containers are completely filled and emptied. Table 15 gives the proportions by volume for standard specified mortars. Table 17 gives the lime : sand mixes required for specified cement : lime : sand mortars and also the proportions in which the lime : sand mixes should be mixed with cement. Table 18 gives the average yield, water content and bulk density of mortars. Proportioning by mass will produce more consistent mortars than volume proportioning, provided that the variation in bulk densities of the materials is checked constantly. 31.3 Mixing For site mixing, mortar is usually mixed in small tilting drum concrete mixers. Mortar pan mills and pan mixers are seldom found on sites and details for their use are not included in this code. When mixing, care should be taken to ensure that the correct quantity of water is used, as too much will produce light shades of mortar; reduced strength and durability may also result. An estimation of the water requirements for a mix may be determined from the average properties of wet mortar given in Table 18.
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Special cement, retarded ready-to-use Consistency, both as regards proportioning of cement : lime : sand and cement : sand mortars, materials and mixing time, is essential to produce good mortar and masonry. Wide variation in mixing and dry-packaged cementitious mixes should be mixed in accordance with manufacturers’ time should be avoided, particularly where instructions. plasticizers are added to the mix. In general, a mixing time of between 3 min to 5 min after all the When colouring agents (pigments) are used, they constituents have been added to the mixer should be should be mixed in accordance with the suitable. Shorter mixing time may result in manufacturers’ instructions. The percentage of non-uniformity, poor workability and low water colouring agent by mass of the cement in the mortar retention. Longer mixing time may adversely affect should not exceed 3 % (m/m), for carbon black, the strength and bond of mortars containing a or 10 % (m/m), for other agents. plasticizer of the air entraining type, owing to 31.4 Use of mortars excessive air entrainment. Generally, where mortar or lime : sand (coarse stuff) Mortars containing cements (except ready-to-use retarded mixes) should be used within about 2 h of is mixed by machine, about three-quarters of the required mixing water and sand should be added to mixing of the cement and water and any mortar not then used should be discarded and not retempered. the mixer; the appropriate amount of lime and/or cement should then be added gradually and allowed If necessary, to restore workability within a 2 h period, mortar can be retempered by adding a small to mix in. This should then be followed by the amount of water, and remixing thoroughly. remainder of the sand and any necessary water to achieve workability. When the mortar is being made Ready-to-use mortars should be used in accordance with the manufacturer’s instructions and following from coarse stuff, about three-quarters of the required mixing water should be added to the mixer, the recommendations in Appendix A of followed by the required quantity of cement, which BS 4721:1981. should be added slowly to ensure a thin paste free If coloured mortar is used, retempering may cause a from lumps. The required quantity of coarse stuff significant colour change of the mortar. should then be added and allowed to mix in, The working life of mortar will be shorter in hot together with any additional water to achieve weather. Fresh mortar should be prepared at the workability. rate it is used so that its workability will remain Admixtures should be used only with the designer’s about the same throughout the day. Mortar that has permission and following the manufacturers been mixed but not used immediately tends to dry instructions. out and stiffen. Loss of water by absorption and evaporation on a dry day can be reduced by wetting When mixing plasticized cement : sand mortars or masonry cement mortars, care should be taken not the boards and covering the mortar. to add too much water at the start, as these mortars All tools and containers should be cleaned and become more fluid as air is entrained. Plasticizers washed after use and when changing coloured should be mixed with part of the mixing water mortar. unless the manufacturer’s instructions specify otherwise. The proportion of mortar plasticizer should be that recommended by the manufacturer of the plasticizer according to the mix and type of aggregate to be used. Table 17 — Ready-mixed lime : sand mixes for specified cement : lime : sand mortars Mortar designation
Type of mortar Specified cement : lime : sand mortar
Lime : sand mix
Gauging of cement with lime : sand mix (coarse stuff)
Proportions by volume
Proportions by volume
Proportions by volume
Mean water demand
L/50 kg cement
i)
1 : 0 to !: 3
1 : 12
1:3
30
ii)
1 : " : 4 to 4"
1:9
1 : 4"
35
iii)
1 : 1 : 5 to 6
1:6
1:6
45
iv)
1 : 2 : 8 to 9
1 : 4"
1:9
60
v)
1 : 3 : 10 to 12
1:4
1 : 12
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NOTE Where mortar of a given compressive strength is specified by the designer, the mix proportions should be determined from tests or the supplier.
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Table 18 — Bulk density, water demand and yield of wet mortars Mortar designation
Type of mortar Cement : lime : sand Specified mix
Yield
Masonry cement : sand Mean Specified mix water demand
Yield
Cement : sand with plasticizer
Mean Specified water mix demand
Yield
Mean water demand
m3/50 kg cement
L/50 kg cement
Proportions by volume m3/50 kg cement
L/50 kg cement
m3/50 kg cement
i)
1 : 0 to ! : 3
0.14
40
—
ii)
1 : " : 4 to 4" 0.19
50
iii)
1 : 1 : 5 to 6
0.25
70
iv)
1 : 2 : 8 to 9
0.37
v)
1 : 3 : 10 to 12 0.49
—
L/50 kg cement
—
—
1 : 2" to 3" 0.15
35
1 : 3 to 4 0.16
40
1 : 4 to 5
0.21
45
1 : 5 to 6 0.24
50
100
1 : 5" to 6" 0.27
55
1 : 7 to 8 0.30
60
140
1 : 6" to 7
65
1:8
65
0.3
—
0.32
—
32 Laying of masonry units
32.2 Joint thickness
32.1 Setting out
The average thickness of both horizontal and vertical mortar joints is dictated by the coordinating size of the masonry units and is normally taken to be 10 mm exclusive of any key in the jointing surface of the masonry units. This joint size allows for irregularities in the masonry units and should accommodate most oversize particles in the fine aggregate whilst being reasonably economical in the use of mortar. Joint sizes may need to be varied from the nominal 10 mm but the joints in any section of work should be kept as consistent as possible. Flanking or abutting work may predetermine the joint size. For example, where a wall is composed of two different types of masonry unit as in the two leaves of a cavity wall, it may be necessary to adjust the joint thickness so that the appropriate courses correspond throughout the height of the wall. Where work is to be built into a framed building, the length and height of a selection of units should be checked to determine whether the joint thickness should be modified from the nominal 10 mm to accommodate any tendency for units to be over or under size.
When setting out masonry, care should be taken to reduce the cutting of masonry units to a minimum and to avoid irregular or broken bond, particularly at openings or in piers. Great care should be taken to ensure accuracy in the setting out of the first course of masonry units in order to avoid subsequent inaccuracies in the finished work. Dimensions should be checked from time to time as the work rises. Masonry units should be laid in true and regular courses. The horizontal distance between cross joints in successive courses should normally be not less than one-quarter of the length of the units but in no case less than 50 mm for bricks or 75 mm for blocks. In lengths of walling between corners, the masonry units should be laid to a string line stretched tight between the corners. To avoid excessive deflection, string lines should be supported at not more than 6 m intervals by tingles. Where corners and other advanced work are raised above the general level, they should be racked back not higher than 1.2 m at one lift and for facing work the whole lift completed in one operation. Advanced work has to be plumbed and the height checked with the gauge rod. Where masonry units are laid on the batter, as in retaining walls, they should be aligned by laying the face of the units to the desired angle, using a tapered profile board. A full masonry unit should be positioned directly beneath a lintel bearing.
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32.3 Achieving good adhesion It is essential to ensure that in any masonry construction adequate adhesion exists between the masonry units and the mortar. Depending on their characteristics, masonry units may be highly porous and, particularly in warm weather, rapidly absorb the moisture from the mortar when laid. In such cases the mortar becomes harsh and insufficiently plastic to accommodate movement of the unit during laying and levelling and it is possible that no adhesion between the unit and the mortar will be obtained.
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Experience has shown that adhesion will be adversely affected when masonry is allowed to dry out rapidly in warm, dry conditions. In such conditions, laying mortar beds in shorter lengths, thus limiting water loss from the mortar before the next course is laid, is advantageous. Wetting may assist in removing dust from the bricks and thus further improve adhesion. However, the bricks should not be over wetted, as this may lead to “floating” on the mortar bed and also to excessive efflorescence and staining of the brick face. In fired-clay brickwork, adjustment of the suction rate of the bricks at the time of laying may be required by the designer for structural reasons. The consistency of the mortar should be adjusted or the bricks should be wetted (docked) for not longer than 2 min just before use (less time may be required, depending on the moisture content of the bricks). In very dry conditions, easier laying and better adhesion of calcium silicate bricks may be achieved by adjusting the consistency of the mortar or dipping the bricks briefly in water just before use. The bricks should not be soaked in water. Concrete masonry units should not be wetted. Instead the consistency of the mortar should be adjusted to suit the suction, if necessary using water-retaining admixtures. For guidance on the characteristics of particular masonry units and appropriate wetting procedures, the manufacturer should be consulted. 32.4 Appearance The achievement of vertical alignment of perpends may require gauging of bricks, particularly for narrow piers; setting out from the base in relation to openings; careful variation of vertical joint width. To avoid a patchy appearance, care should be taken to mix facing masonry units from different consignments (see 30.2). Colour variation in different batches of mortar, which will also lead to uneven appearance, may be reduced by consistent mixing and preparation (see clause 31). When laying masonry units, the mortar should not be allowed to encroach on their exposed faces, since it is not easily removed when dry. This applies particularly to open-textured masonry units. Wherever practicable, facing work racked back should not be left overnight before being brought up level. The appearance of finished masonry may be affected by failure to protect the work during construction (see 35.2).
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32.5 Jointing Jointing as the work proceeds is preferable to pointing. Mortar joints on the face of the masonry should be to the required profile (see 27.7 and B.3). The joints should be tooled to compact the mortar, to give a firm joint between mortar and unit and to give the desired profile. Tooling helps to improve the durability of the mortar and the rain-shedding capacity of the wall. Rendering may be satisfactorily applied to masonry units but it may be preferable in certain circumstances to provide additional mechanical key by raking out joints or by using keyed units. 32.6 Pointing If pointing is desired, the joints should be well raked out to a depth of between 10 mm and 15 mm as the work proceeds to give an adequate key. Joints should be brushed out to remove dust and loose material and should be lightly wetted using a brush. The mortar used for pointing should not be stronger than that used when constructing the wall. It is desirable to carry out pointing from the top of the wall downwards. 32.7 Bricklaying Bricks should be laid on a full bed of mortar and all cross joints and collar joints should be filled. Immediately after the brick is laid, excess mortar should be struck off the external face of the work and off the internal faces of leaves of cavity walls. Care should be taken to ensure that mortar is not scraped into the exposed face of the brick. Any accidental smears should be lightly brushed off the face after the mortar has taken its first set. Where grout is used to fill collar joints or voids within the thickness of the wall, it should follow the recommendations for mortar given in clause 23. Only enough water to make a pourable mix should be added, as excess water may cause segregation and undue shrinkage. For any given mortar, the water content should be appropriate to the suction rate of fired-clay bricks (see 32.3). The daily lifts should be regulated accordingly. Unless otherwise specified, frogged bricks should be laid frog up and the frogs should be completely filled with mortar. The position and filling of the frogs are important, as both can affect the strength and sound insulation of the wall. Cellular bricks should be laid with their cavities downwards and unfilled. Reinforced and prestressed brick masonry should be constructed following the recommendations of BS 5628-2.
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32.8 Blocklaying
32.10 D.p.cs, cavity trays and flashings
Solid and cellular blocks should normally be laid on a full bed of mortar (not furrowed) and cross joints and collar joints should be filled. Shell bedding (see 2.25) may be used only by permission of the designer, since it affects the strength of the finished wall. Sufficient mortar should be used to ensure that all keys in the joint surface are properly filled. Bed joints of hollow blocks should be shell bedded, with or without mortar strips under the cross webs; the vertical joints may be either full or shell bedded. The mortar stiffness used should be adjusted to ensure good adhesion (see 32.3) or, for heavy blocks, to prevent extrusion from bed joints. For fair-faced work, excess mortar should be struck off immediately after the block is laid. Care should be taken to ensure that mortar is not scraped into the exposed face of the block. Any accidental smears should be lightly brushed off the face after the mortar has taken its first set. Blocklaying can be facilitated by placing the blocks on stagings at the same height as the work, which enables the blocklayer to transfer the unit horizontally rather than lifting each block from floor level. Where large or heavy blocks are to be used, consideration should be given at an early stage to the problem of their handling. Whilst the blocklayer may be able to lay a small number of heavy units without difficulty, he cannot continue the process repeatedly without either risking injury or losing efficiency. The provision of lifting gear and other specialized handling equipment may be necessary. Reinforced and prestressed block masonry should be constructed following the recommendations of BS 5628-2.
32.10.1 D.p.cs should be laid on a smooth bed of fresh mortar, unless they are required to accommodate differential sliding movements between the units on either side of them, in which case the mortar bed should be trowelled smooth and allowed to set, and then cleaned off before the d.p.c. is laid. It is essential not to use coarse aggregates which might damage the d.p.c. Joints or perforations in the underlying course should be flushed up. This is particularly important where a flexible membrane is used, since the membrane is in danger of being torn or punctured if it is forced into hard-edged cavities by the load of the wall above. It is essential to joint all laps other than those in simple horizontal work, and all such unsealed laps should not be less than 100 mm long. Care should be taken not to pierce d.p.cs and cavity trays by services, reinforcement, fixings, etc. and not to bridge d.p.cs by pointing, rendering, plastering, tiling, etc. 32.10.2 For bitumen-coated materials, the surfaces to be jointed should be heated until the bitumen is softened and then pressed together. For pitch and bitumen polymer materials, an adhesive recommended by the manufacturer should be used as directed. For polyethylene d.p.cs, a double-sided adhesive tape should be used. Joints for lead d.p.cs should be formed either by welting or burning whilst joints for copper and zinc based materials should be formed either by welting or soldering. 32.10.3 Asphalt should be dressed up to d.p.cs and into a chase. The asphalt should preferably be sufficiently fluid to adhere to the material of the d.p.c. In this case, polyethylene-based materials should not be used, since they will melt and holes will be formed. 32.10.4 Where a sufficiently durable material, such as metal, is to be used, it should be allowed to project beyond the surface of the wall by 10 mm. All d.p.cs except brick d.p.cs should project a minimum of 5 mm beyond the external face of the wall.
32.9 Reinforced block lintels Reinforced block lintels should be made from U-shaped blocks in which reinforcement is laid to the full length, including bearings. The blocks should be filled with concrete and the joints between them should be filled with mortar. Temporary support will be required during construction and until the concrete infill has gained sufficient strength.
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32.10.5 Wherever possible, all cavity trays should be supported, either by laying directly on existing supporting structures, e.g. the concrete slab upon which the inner leaf is built, or by building up the base of the cavity to form a suitable support. 32.10.6 Weepholes should be formed by leaving open perpend joints at not less than 1 m intervals, with not less than two weepholes over each opening. Care should be taken to avoid holes being blocked by mortar droppings; where necessary, they should be cleaned out. This is particularly important where the use of cavity fill is anticipated. 32.10.7 Wherever possible, flashings should be built in as the work proceeds. 32.11 Cavity walls 32.11.1 The purpose of a cavity in a wall is to prevent water penetrating to the inner surface. The inner face of the outer leaf of a cavity wall will often be wet during the life of a building, particularly in exposed situations. 32.11.2 When building a cavity wall, it is essential that the cavity is not bridged by any material which could transmit water from the outer to the inner skin. Accumulations of mortar droppings in the cavity should be prevented by using laths, drawholes, fine sand and/or thick rope. Any mortar which does fall on wall ties or cavity trays should be cleaned off and the bottom of the cavity should be cleared out daily through temporary openings. It may be found more convenient to leave these openings in the inner leaf, so avoiding any patchiness on the finished facing work. Cavity clearing operations should be carried out carefully to avoid damage to d.p.cs. 32.11.3 Both leaves of a cavity wall should be raised at the same time. The difference between the heights of the two leaves should be: a) about the vertical spacing of consecutive rows of ties, for vertical twist ties; b) not greater than six block courses, for double triangle and butterfly ties; c) not greater than 225 mm in a section of wall where pressed steel lintels are installed, to avoid twisting the lintel. 32.11.4 The wall ties should be placed in the bed joint of the appropriate course of the higher leaf as it is built and not pushed in after the units are bedded. Wall ties should be bedded a minimum of 50 mm in each leaf and have a slight fall to the outer leaf.
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32.11.5 It is essential that the cavity is free from protrusions which would form ledges and thus facilitate the build up of mortar droppings. If a bond pattern is desired which necessitates the use of snap-headers, these should be either accurately cut, sawn or purpose made. The cavity should extend for at least 150 mm below the lowest d.p.c. If cavity walls are built off the foundation, they should be filled in solid to external ground level. At the base of the cavity every fourth vertical joint in the outer leaf of external walls may be left open to drain the cavity. 32.12 Slips 32.12.1 Preparation of surfaces. It is essential to clean all surfaces of the slips and the substrate thoroughly, ensuring that they are free from dust, particles, grease and mould oil, and remove the laitance from any concrete surface to expose the aggregate. Adequate cover to reinforcement should be maintained. Bituminous paint should never be applied to concrete surfaces, as this would severely affect the adhesion between the concrete and the slips. 32.12.2 Application of adhesive. Reference should be made to the manufacturer’s instructions but generally the adhesive should cover the whole of the back face of the unit and be continuous against the concrete face. (Application in the form of dabs of adhesive will cause pockets which may trap water and so lead to frost damage.) Movement joints should not be bridged by adhesive. 32.12.3 Types of adhesive system. The main types of adhesive system used are epoxy resin systems, polyester resin systems and systems based on cementitious mortars with styrene/butadiene rubber (SBR). Epoxy resin systems have a working life of 2 h to 3 h, with full cure developing in 24 h. They should not be used when the ambient temperature is below 4 °C. There are important differences between proprietary formulations, such as the relative proportions of individual components and the tolerable degree of moisture which is acceptable. For site work, the risk of error should be minimized by the provision of prepared proportions of each individual component, which should be mixed thoroughly in the correct order. The tolerance of a system to damp conditions should be checked by referring to the manufacturers.
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Polyester resin-based adhesive systems have a working life varying from 5 min to 24 h, depending on the ratio of resin to hardener, which is generally quite critical. Tolerance to moisture also appears to vary widely. However, as with epoxy resin systems, polyester resin adhesives, when properly mixed and applied, rapidly develop a high strength bond which is resistant to water and most chemicals. In systems based on cementitious mortars with SBR, the mortar is prepared by mixing one part by mass of Portland cement with 2" to 3 parts of clean sand, i.e. sand as free as possible from clay, with the gauging water wholly or partly replaced by SBR. The surfaces to be joined should be prepared by coating with a slurry of cement and SBR. Whilst this is still tacky, the mortar should be buttered on to the grouted surfaces and the slips pressed into place. It should be noted that, as with conventional mortars, the strength of the bond will be slow to develop at low temperatures. 32.13 Masonry bonds To maintain a regular masonry bond and neat appearance at quoins, reveals, joints, etc, special bonding units or closers may be required. A number of special shaped units are manufactured (see BS 4729). However, it is advisable to consult the manufacturer at an early stage about the availability of such units.
33 Constructional details 33.1 Quoins and reveals When constructing quoins and reveals, particular care should be taken to check gauge and verticality as the work proceeds. The use of toothings should be avoided. Quoins and reveals in vulnerable positions should be protected during the period of work on site. 33.2 Piers Broken bond should be avoided in piers and the bonding of the quoins should be such as to preserve symmetry in the appearance of the work. Piers which are required to strengthen the wall should be properly bonded or tied into the parent wall. 33.3 Sills and thresholds One-piece sills or thresholds, e.g. stone or concrete, should be bedded with mortar only below the ends or stoolings, to prevent fracture of the sill in the event of thermal movement and differential settlement. The open joint should be pointed with mortar on completion of the masonry. Timber, pervious or jointed sills or subsills should be provided with a d.p.c. for the full length and width of the sill bed. Sills should be adequately weathered to prevent water lying on their upper face.
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33.4 Lintels Lintels should have adequate bearing on the wall at the sides of the openings (see 19.3) and should be bedded on mortar. They should not bear on a short length of cut block. Precast concrete lintels should have matured and dried before being built into the wall, to prevent cracking at the ends due to drying shrinkage of the lintel. Cast in situ lintels of reinforced concrete or of reinforced masonry (see 32.9) should be propped and allowed sufficient time to develop adequate strength before they are made to carry superimposed loads. Where composite lintels, e.g. prestressed concrete plank lintels, are used, no chase or hole should be formed in the area comprising the composite section nor should any inclusion, such as joists, be built into this section, with the exception of d.p.c. materials which intrude not more than one-quarter of the width of the bed joint or 30 mm, whichever is the lesser. Installation should follow the recommendations of the manufacturer. 33.5 Arches When building an arch, temporary support should be provided and the arch should be allowed sufficient time to develop adequate strength before it is made to carry superimposed loads. Care should be taken to butt up the voussoirs, either by using rubbers or by varying the thickness of the joint (see 27.6). In cavity construction, cavity trays should be of malleable material, curved to follow the arch, or preformed. 33.6 Toothing and indenting Where future extensions are required to be provided for in a wall, the course terminating in a header or bat should have that header, and the adjacent closer, if one occurs, bedded in designation iv) mortar so that these units can be easily removed to enable the bond to continue. Alternatively, units can be left projecting or omitted and where this is done, the upper exposed surfaces of the units should be weathered in designation iv) mortar. 33.7 Connections between walls and partitions Walls and partitions should generally be bonded, tied or dowelled to one another at angles and junctions, but particular care should be taken to construct joints as shown on detailed drawings, as they may be required to accommodate movement in a particular direction or to be totally discontinuous. Where it is necessary for a partition to be connected to an adjacent wall or column, this should be done by toothing or block bonding unless otherwise specified.
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33.8 Movement joints Movement joints should be formed as the work proceeds. For efficiency in the performance of sealants, it is essential that the joint is properly designed and prepared (see 20.3 and 20.4). Back-up material should be placed within the joint in such a way that the distance of its face from the joint face will allow the correct depth of seal to be used. The faces of the joint to which sealant is to be applied should be clean and free from loose material; they should also be dry unless otherwise specified. Application of primer and sealant should be in accordance with the manufacturer’s instructions. Care should be taken to apply the sealant to the full specified depth, avoiding bubbles. The sealant should adhere to each side of the joint. 33.9 Fixing of frames Frames may either be built in when the walling is being built or fixed after the opening has been formed. When built in with the walling, temporary strutting of the frame is necessary to prevent distortion during the process. The horns may be cut off or built in, providing the building-in does not weaken the structure of the wall. Cramps should be fixed to the backs of the posts and built into the walling; it is not usually necessary to use fixings at the heads of door frames, except, perhaps, with very wide doorways. Care should be taken in building-in frames to prevent staining by mortar splashings, especially if the wood is not to be painted.
34 Provision of services, including fixings and chases Chases, fixings and holes in masonry may seriously affect the strength of the masonry (see 19.6). As far as is practicable, in order to eliminate unnecessary cutting away and making good, sleeves and chases should be provided during the erection of the masonry. This applies especially to electric ductwork. In external walls, all sleeves and pipes should preferably be laid with a fall towards the outside. No services should be run within the cavity of cavity walls. The installation of services should be completed before plastering or other finishing work is begun.
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Where chases have to be cut, suitable power tools which do not operate by heavy impact, e.g. rotary tools, should be used so that the depth recommended in 19.6 is not exceeded. Fixing units (bricks or blocks), where required, should be built into the wall or partition in the correct positions for skirting, rails and other items of joinery, fittings, etc.
35 Protection against damage during construction 35.1 General Care should be taken to anticipate and prevent damage or disfigurement to the finished work due to weather, subsequent building or other operations. Care should also be taken over the siting of hoists. The arrisses around openings to be used by barrows, etc. should be protected. Temporary support to walls may be required during construction to prevent damage by wind. Work below ground poses particular problems. It is essential to prevent contact with strong salt solutions, e.g. those used for clearance of snow and ice. 35.2 Protection against rain Newly erected masonry should be protected to prevent the mortar being washed out of the joints by rain. Walls should be prevented from becoming saturated by covering the top of the wall with tarpaulins or other waterproof sheets; this is particularly important to minimize the incidence of efflorescence and lime bloom. When any working platform is not in use, the inner board should be turned away from the wall to prevent the splashing of the wall face. 35.3 Work in cold conditions Generally, when masonry construction is carried out during freezing weather, proper facilities should be made available for preparing the mortar, protecting the materials and protecting the fresh masonry work against frost damage. If there is a break in the construction programme during the winter period, unfinished masonry may be exposed to saturation and freezing for a considerable period of time.
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Where work is to be carried out in frosty or freezing conditions, particular attention should be paid to protection of the materials and finished masonry, since water in the mortar mix and masonry units may cause considerable damage to the masonry if it is allowed to freeze. During cold weather, the mortar will be slow to gain strength and, therefore, any precautions should be maintained until the mortar has gained sufficient strength to resist being frozen. Because of the possible damage that may occur to newly constructed masonry in cold weather, no masonry units should be laid when the temperature is at or below 3 °C, unless precautions are taken to ensure that the mortar has a minimum temperature of 4 °C when laid and that the masonry is protected from becoming frozen until the mortar has hardened. In addition, precautions may be required where the temperature is above 3 °C when the mortar is laid but where the subsequent temperature may fall below freezing before the mortar has hardened, e.g. overnight. The precautions to be taken should be agreed with the designer and may include the following. a) Protection of the mixing plant, at times by a heated enclosure. b) Heating the aggregate and water before use. When this is done, the mortar should be used immediately after mixing, before it loses all its heat. The water temperature should normally not exceed 60 °C.
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c) Protection of the finished work by an insulated waterproof covering. d) Provision of complete heated enclosures to protect both masonry and operatives. In this condition, both the mixing plant and materials should, ideally, be housed within the enclosure. The following precautions should generally be implemented in freezing conditions: 1) the masonry units in the stack should be protected from becoming saturated; 2) the sand should be protected by waterproof insulating covers (insulating quilts, tarpaulins or similar) supported clear of the sand to improve thermal insulation. NOTE Unprotected sand may remain frozen some considerable time after air temperature has risen above freezing point.
Antifreeze admixtures, particularly calcium chloride, should not be used (see 23.3).
36 Supervision The design recommendations given in section 3 of this code assume the quality of workmanship described in section 4. Supervision should ensure that this quality is achieved.
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Appendix A Determination of movement in masonry A.1 General This appendix gives information on the various movements that can occur in masonry. It should be noted from the start that it is extremely difficult, if not impossible, to predict with any degree of certainty the movement that will actually occur. This movement is a complex combination of movements caused by such factors as temperature and moisture variations (see A.2). Furthermore, each movement is controlled to some extent by the degree of restraint to which the masonry is subjected. To complicate matters further, the actual effect on movements of the same basic restraint may well vary according to the general shape of the building and in many cases cannot be quantified. The determination of movement is thus a complex problem which cannot be solved simply by adding or subtracting individual values for thermal movement, moisture movement, creep, deflection, etc. The various individual movements are treated separately in A.4 to A.6. Any estimation of movement has to rely to a great extent on engineering judgement, since many factors, such as the temperature and moisture content of the material at the time of construction, weather conditions and degree of restraint, are unpredictable. A.2 Determination of total movement within a wall A.2.1 General To determine the movement that is likely to take place within an actual wall, the individual movements described in A.4 to A.6 have to be considered in combination. An estimate of the total movement may be made by summing all the potential free movements. However, thermal and moisture movements are not directly additive. For example, a wall which expands due to thermal or moisture action alone generally becomes cooler when wetted by rain. The exact effect of such a combination is in practice extremely difficult to determine. All that can be said is that the maximum thermal and moisture movements should not be added together to arrive at the total effective free movement.
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A.2.2 Total effective free movement for fired-clay masonry For fired-clay masonry where the ambient temperature remains reasonably constant, e.g. for internal walls, the long term or time-dependent movement described in A.5.2.2 predominates. Since this is an expansive movement, the masonry is unlikely to develop tensile cracks, except in short returns of less than 1 m in length. External masonry of fired-clay masonry units will be subjected to the effects of thermal expansion superimposed on the long term movement. A.2.3 Total effective free movement for concrete and calcium silicate masonry Owing to the number of factors involved, it has not been found practicable to recommend coefficients for total effective free movement of concrete and calcium silicate masonry. However, where joints are provided in accordance with 20.3.2.3 and 20.3.2.4, the total effective free movement will be small and detailed calculations are unnecessary. A.3 Determination of spacing and widths of movement joints There is no convenient mathematical expression for determining the position of movement joints in masonry. However, the basic principle is that the distance between joints should be such that the longitudinal strain induced in the wall is no greater than the strain capacity of the wall. Owing to the difficulty of computing joint spacings on this basis, recommended spacings based on practical experience have been given in clause 20. It is essential that the maximum movement in the masonry should be no greater than the permitted movement in the joint sealant. Thus: Length of masoary Permitted strain in sealant --------------------------------------------------- = --------------------------------------------------------------------------Width of joint Effective strain in wall
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A.4 Thermal movement The theoretical free movement due to thermal effects, which is reversible, is equal to the temperature range multiplied by the appropriate coefficient of thermal expansion and the length [see Figure 16(a)]. However, the movement that actually occurs within a wall after construction depends not only on the range of temperature but also on the initial temperature of the masonry units when laid. This will vary according to the time of year and the exact conditions during the construction period and, in some cases, how soon after manufacture the masonry units are used, i.e. when they come straight from the kiln or curing chamber. Thus, in order to determine the potential free movement that could occur in a wall, some estimate of the initial temperature and the likely range of temperature should be made. This potential free movement then needs to be modified to allow for the effect of restraints. Table 19 indicates typical ranges for coefficients of thermal movement. Some estimate of the actual value for the particular material being used should be made. In many instances, this information may be obtained from the manufacturers. Table 19 — Linear thermal movement of masonry units and mortar Material
Fired-clay masonry units (see note 1) Concrete masonry units (see note 2) Calcium silicate masonry units Mortars
Coefficient of linear thermal movement/°C
4 to 8 × 10–6 7 to 14 × 10–6 11 to 15 × 10–6 11 to 13 × 10–6
NOTE 1 Thermal movement of fired-clay masonry units depends on the type of clay. NOTE 2 Thermal movement of concrete masonry units depends on the type of material and the mix proportions.
The longitudinal coefficient of thermal movement of masonry may be taken to be the same as that of the constituent masonry units. Movement in the vertical direction may be determined by summing the values obtained by multiplying the dimensions of the masonry units and the mortar by the respective coefficients. It should be borne in mind that the magnitude of movement in the horizontal and vertical directions will differ when the coefficients for mortar and masonry units are not the same and when the masonry units’ height and length are unequal.
A.5 Moisture movement A.5.1 General The moisture movement of fired-clay masonry units and calcium silicate or concrete masonry units differ in magnitude and in kind. They have therefore been dealt with separately in A.5.2 and A.5.3. A.5.2 Fired-clay masonry units A.5.2.1 Wetting movement. It has been shown that fired-clay masonry units can exhibit small reversible dimensional changes due to changes in moisture content. The effective movement that occurs within a wall is basically controlled in a similar way to thermal movements, i.e. by minimum, initial and maximum moisture contents. Once again, the actual movement will be modified by the effect of any restraints. The typical range of movement to be expected is generally less than 0.02 %, which is comparatively insignificant. A.5.2.2 Long term expansion. Although it is found that the general wetting movement is extremely small in fired-clay masonry units, there is an irreversible expansion which occurs as a result of adsorbing7) moisture from the atmosphere. This will occur in both internal and external walls but may take place slightly more quickly in the latter. The rate of expansion is at its greatest just after the masonry units have cooled and decreases thereafter. The amount of expansion depends on the type of clay and the degree of firing. The actual movement within a wall will depend on the degree of restraint and the amount of creep that has taken place in the mortar. A.5.3 Concrete and calcium silicate masonry units The potential free movement that can occur in concrete and calcium silicate masonry units depends on the minimum, initial and maximum moisture contents [see Figure 16(b)]. An additional range is shown which represents the limits for compliance with drying shrinkage test requirements in British Standards for these units. However, the drying shrinkage test described in BS 187 and BS 6073-1 determines the shrinkage of units-between saturated and oven dry states, whereas in practice a wall is seldom totally saturated. Thus the free movement may be expected to be less than the movement encountered during a drying shrinkage test.
7) Adsorption
is the term used to describe the bonding of water molecules to the molecules of the masonry material. It should not be confused with absorption, which refers to the entry of water molecules into the pores of the masonry.
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In considering Figure 16(b), it may be seen that the potential free movement within a wall is related to the moisture content at the time of laying. Since concrete and calcium silicate masonry units have a general tendency to shrink as they dry out, it is clear that keeping these masonry units as dry as practicable before and during construction will reduce any subsequent movement. Also, the expected movement may be less for walls built under cover than external walls, subject to the relative humidity. The potential free movement may be modified by restraints. It should be noted that such restraints, particularly at the end of a wall, are likely to increase the tensile stresses in the wall. Table 20 indicates the range of drying shrinkage for various masonry units. The higher figures are the limits specified in the appropriate British Standards for quality control purposes and should not be taken to represent the movement of units in a wall. Table 20 — Moisture movement of concrete and calcium silicate masonry units Material and type of masonry unit
Shrinkage as percentage of original (dry) length %
Autoclaved aerated concrete masonry units Other concrete masonry units Calcium silicate bricks
0.04 to 0.09 0.02 to 0.06 0.01 to 0.04
NOTE These figures are obtained from tests carried out as described in BS 1881-5.
A.5.4 Mortar The free moisture movement of mortar is similar to that of concrete masonry units, although the potential free movement is likely to be greater, since initial moisture loss will not take place before construction [see Figure 16(c)]. The effect of mortar on longitudinal movement may be neglected.
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Typical shrinkage values for mortars are given in Table 21. The actual values will depend on the constituents of the mortar, the proportions of the mix and the ambient relative humidity. For convenience, however, the lower values in the table may be taken to apply to mortars in external walls and the higher values to mortars in internal walls. The resulting movement of internal walls may generally be neglected, since they are unlikely to become wet after drying out initially. Table 21 — Shrinkage of mortars due to change in moisture content Stage
Shrinkage %
Initial drying Subsequent reversible movement
0.04 to 0.10 0.03 to 0.06
It should be noted that the values given in Table 21 relate to unrestrained mortar. In practice, movement in the horizontal direction will largely be controlled by the surrounding masonry. However for fired-clay masonry, the effect of the mortar shrinkage may counteract the long term expansion described in A.5.2.2. Movement in the vertical direction will usually be unrestrained and will thus contribute to the total movement of the masonry in that direction. A.6 Movement due to carbonation An additional shrinkage of concrete masonry units and mortar can occur as a result of carbonation of the cement by atmospheric carbon dioxide. The extent of carbonation and the subsequent movement depends on the permeability of the concrete and on the ambient relative humidity. In dense masonry units and in autoclaved masonry units, the magnitude of this movement is extremely small and may be neglected. In unprotected open textured masonry units and mortar, the shrinkage due to carbonation may be between 20 % and 30 % of the initial free moisture movement.
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Figure 16 — Factors affecting movement
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Figure 16 — Factors affecting movement (continued)
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Figure 16 — Factors affecting movement (continued)
Appendix B Masonry bonds and joint finishes B.1 Brick masonry bonds B.1.1 English bond English bond shows on both faces alternate courses of headers and stretchers [see Figure 17(a)]. B.1.2 Flemish bond Flemish bond shows on the face alternate headers and stretchers in each course [see Figure 17(b)]. It may be built as a “single Flemish bond”, which shows Flemish bond on both faces of the wall.
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B.1.3 English garden-wall bond English garden-wall bond shows a sequence of three courses of stretchers laid with half lap to one course of headers. B.1.4 Flemish garden-wall bond (Sussex garden-wall bond) Flemish garden-wall bond shows on both faces a sequence of three stretchers to one header in each course of a full brick wall [see Figure 17(c)]. In thicker walls, one face is formed in English bond. B.1.5 Heading bond (header bond) Heading bond consists of bricks with their ends showing on the face of the wall, laid with a half lap of the brick width [see Figure 17(d)]. B.1.6 Quetta bond Quetta bond is used for walls a minimum of one and a half bricks thick and consists of alternate stretchers and headers arranged to leave a series of vertical voids in the wall thickness, in which is placed vertical reinforcement, the voids being filled with grout or fine concrete as the work proceeds [see Figure 17(e)]. B.1.7 Rat-trap bond Rat-trap bond shows bricks laid on edge, each course consisting of alternate headers and stretchers. It has a similar appearance to Flemish bond and may be vertically reinforced in the same way as Quetta bond [see Figure 17(f)].
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Figure 17 — Brick masonry bonds © BSI 11-1999
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B.2 Block masonry bonds B.2.1 Running or stretcher bond Running or stretcher bond requires block thickness to be equal to half block length. Half blocks at wall ends [see Figure 18(a)].
B.2.2 Thin stretcher bond Thin stretcher bond requires cut-block closers or quoins at corner and half blocks at wall ends [see Figure 18(b)]. B.2.3 Off-centre running bond Off-centre running bond requires three-quarters or two-thirds cut blocks at wall ends [see Figure 18(c)].
Figure 18 — Block masonry bonds
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B.3 Joint finishes The principal types of joint finish used for brick and block masonry are shown in Figure 19.
Figure 19 — Joint finishes
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Index In this index references are to clause, appendix, table and figure numbers. Access for the disabled 3 Accidental loading 18.1 Accuracy in building 3, 17.1 Acoustic properties 17.1, 26 Adhesion design 17.1, 17.5 workmanship 32.3 Admixtures mix design 23.2.1, 23.3 specification 6.4 workmanship 31 Adsorption 20.1, Appendix A Aggregates effect on d.p.cs 21.5.7 mix design 23.1, Table 15 specification 6.3 storage on site 30.4 workmanship 32.2, 32.10.1 Airbricks design 27.10 specification 12 Alternative components 4 Alternative materials 4 Alternative methods 4 Analysis of structures 3 Anchorages design fixed supports 18.4.2.2, Figure 5 floors Figure 7 roofs Figure 7 simple supports 18.4.2.2, Figure 5 protection against corrosion 22.7.1, Table 14 specification 8, Table 1 types 19.4, Figure 8 Appearance of facing work 32.4, 32.8 Arches design 27.6 workmanship 33.5 Architectural features design 27.2 effect on durability 22.5 effect on rain penetration 21.3.1, 21.3.2.7 Balcony thresholds 21.5.6, Figure 12(f) Bat 2.1 Bearings design floors 19.1 lintels 19.3 walls beneath structural members 20.2.2 walls subjected to concentrated loads 18.3 workmanship 32.1, 33.4
8) Where
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Bed joints 2.24.1, 26.2.1, 32.8, 32.11.4 Blocks, concrete8) see also Masonry units design adhesion 17.5 cut to match facing masonry 27.5 durability 22.6, Table 13 frost attack 22.3.4 movement Appendix A selection 17.6, Table 6 slips 27.3 sulphate attack 22.4 specification 5.1 workmanship adhesion 32.3 handling 32.8 laying 32.8 slips 32.12 Blockwork, concrete see also Masonry design masonry bonds 27.1.3 movement joints 20.3, 2.4 resistance to rain penetration 21.3.2.5, 21.3.3 Bonding ties protection against corrosion 22.7.1, Table 14 specification 8, Table 1 workmanship 33.7 Bricks see also Masonry units calcium silicate design adhesion 17.5 durability 22.6, Table 13 frost attack 22.3.3 movement Appendix A selection 17.6, Table 6 sulphate attack 22.4 specification 5.1 workmanship adhesion 32.3 laying 32.7 concrete8) design adhesion 17.5 durability 22.6, Table 13 frost attack 22.3.4 movement Appendix A selection 17.6, Table 6 sulphate attack 22.4 specification 5.1 workmanship adhesion 32.3 laying 32.7 damp-proof course 10, Table 12, Table 13
fired-clay design adhesion 17.5 durability 22.6, Table 13 frost attack 22.3.2 movement Appendix A selection 17.6, Table 6 slips 2.27.4, 27.3 sulphate attack 22.4 water absorption 22.3.2 specification 5.1 workmanship adhesion 32.3 laying 32.7 slips 32.12 pistol 2.27.3, 27.4 Calcium chloride, prohibition of 6.4.2, 23.3 Cappings definition 2.2 design 21.7 durability 22.1.3, Table 13(I) effect on durability of masonry 22.5 Carbonation 20.1, Appendix A Cast stone 13, 15 Cavity closers 21.5.4 Cavity insulation foreword, 21.3.1, 21.3.2.6, 21.4.2, 21.4.6, 21.5.5, 25.3, 32.10.6 Cavity trays definition 2.3 design 21.4.2, 21.4.3, 21.4.4 in arches 27.6 in chimneys 21.5.8 in external wall becoming internal wall 21.8 in parapets 21.5.7 in structural frames 21.9 over openings 21.5.5 protection against corrosion 22.7.1, Table 14 workmanship 32.10.5 Cavity walls see also Masonry and Walls definition 2.28.2 design area of walls with edge restraint 18.4.2.1 condensation 25.6 damp-proof courses 21.4.2 ducts 27.10 exclusion of moisture 21.1, 21.3.2.6, 21.3.2.7 fire resistance 24, Table 16(C) and Table 16(D) projecting features 27.3
a clause refers both to concrete blocks and concrete bricks the term precast concrete masonry units is used for brevity.
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sound insulation 26.2.1 support conditions 18.4.2.2 wall ties 19.5 workmanship 32.11 Cellular masonry units 18.3, 32.7 Cement mix design 23.1, 23.2, Table 15 specification 6.1 storage on site 30.3 sulphate attack 22.4 workmanship 31 Chases design 19.6, 27.9 effect on stability 18.4, 18.5, 19.6 placing of movement joints 20.3.2.5 workmanship 34 Chimneys design damp-proof courses 21.5.8 durability 22.1.3, Table 13(H) stability 19.7 Cladding effect on durability of masonry 22.1.1, 22.5 exclusion of moisture 21.3.2.1, 21.3.2.7, Table 11(B) Cleaning masonry 3 Cloaks, pre-formed 21.4.5 Closer 2.3, 32.13, Figure 17 see also Cavity closer Cold bridges 25.5 Collar joints 2.24.2, 32.7 Collar-jointed walls 2.28.3, Table 8 Colouring agents 6.4.4, 31.3 Columns 18.1, 18.2, 18.3 Composite action 18.1 Concentrated loads 18.3 Condensation 25.6 Connections see also Anchorages, Dowels, Fixings and Movement joints design floors 19.1, Figure 7 general 18.1 roofs 19.2, Figure 7 sound insulation 26.2.2 stability 18.4.2.2, 18.5, Figure 3 and Figure 4 workmanship 33.7 Control joints see Movement joints Copings damp-proof courses 21.5.7 definition 2.5 design 21.7 durability 22.1.3, Table 13(I) effect on durability of masonry 22.1.1, 22.5 specification 15 Corrosion, protection of components 22.7, Table 14 (Table 9 for wall ties) Courses 2.6, 27.1.1, 32.1, 32.2, 33.6 see also String courses Corbels 27.8
© BSI 11-1999
Creasing, tile 2.5, 21.7 Cross joint 2.30.3, 32.1
Exposure, Severe/Very Severe effect on choice of wall ties 19.5 effect on durability 21.1.1, 22.1.3, 22.4 effect on protection of metal components 22.7.1 effect on quality of workmanship 21.3.2.2
Damp-proof courses (d.p.cs.) design general 21.4 positioning 21.5 above ground level 21.5.2 balcony thresholds 21.5.6, Figure 12(f) below ground level 21.5.1 cappings 21.7 chimneys 21.5.8, Figure 9 copings 21.7 external wall becoming an internal wall 21.8, Figure 12(h) freestanding walls 18.4.1 jambs of openings 21.5.4, Figure 12(a), Figure 12(c) openings 21.5.5, Figure 12(d), Figure 12(e) parapets 21.5.7, Figure 12(g) sills 21.5.3, Figure 12(a), Figure 12(b) slip planes 20.3.1 slips 20.2.4 structural frames 21.9, Figure 12(i) durability (masonry d.p.c.s) 22.6, Table 13(B) Specification 10, Table 12 storage 30.6 sulphate attack 22.4 workmanship 32.10 Datum 2.7, 28.2 De-icing salts 22.3.1, 22.3.3 Design 17 to 27 factors to be considered 17.1 Docking bricks 17.5 Doors see also Openings design exclusion of moisture 21.3.2.6, 21.5.4 placing of movement joints 20.3.2.5 stability 19.3 workmanship 33.9 Double-leaf walls 2.28.3, Table 8, 27.2.3 Dowels design 20.3.1 protection against corrosion 22.7.1, Table 14 specification 8, Table 1 types 19.4, Figure 8(c) Driving rain index see Wind-driven rain index Dry-packaged cementitious mixes 6.6 Ducts 27.10, 34 Durability 22
Factors affecting design 17.1 Fair faced work 2.9, 32.8 Finishes 17.1, 17.3, 20.3.1, 21.3.1, 21.3.2.1 Fire resistance 24, Table 16 Fittings 19.6, 20.3.1, 27.9 Fixing units 2.27.1, 34 Fixings design 19.6, 20.3.1, 21.4.7 protection against corrosion 22.7.1, Table 14 specification 8, Table 1 types 19.4, Figure 8 workmanship 32.10.1, 34 Flashings design 21.6 for cappings 21.7 specification 16 workmanship 32.10 Floors connections 19.1, Figure 7 concrete 19.1, Figure 7(c), 21.4.2 placing of movement joints 20.2.1, 20.3.2.5 stability 18.1 suspended timber 19.1, 20.2.1 Flue blocks 5.1, 27.1 Flues 12, 19.7, Figure 9 Foundations 3, 17.4, 18.1, 22.1.3 Frames door 19.3, 20.3.2.5, 21.3.2.6, 21.5.4, 33.9 structural 20.2.3, 21.9, Figure 12(i) window 19.3, 20.3.2.5, 21.3.2.6, 21.5.4, 33.9 Freestanding walls definition 2.28.4 design 18.4.1 durability 22.1.3, 22.4, 22.6, Table 13(J) Frogged masonry units 18.3, 32.7 Frogs 2.10, 19.2, 32.7 Frost attack 21.3.2.1, 22.1.2, 22.1.3, 22.3, 22.5, 23.3, 35.3
Efflorescence 2.8, 22.1.3, 35.2 Exclusion of moisture 21 Exposure categories 21.2, Table 10
Handling 17.6, Table 6, 32.8 Header 2.26.2, B.1, Figure 17 Holes 19.6 Hollow masonry units 18.3, 27.1.3, 32.8
Gables 18.4.2.1 Gratings 12, 27.10 Grouted cavity wall 2.28.5, Table 8
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Impact resistance 17.3 Indenting 2.11, 33.6 Inspection chambers 22.1.3, Table 13(L) Insulants 21.3.2.8, Table 11(B), 25.3 Jambs 2.12, 21.5.4 Jointing 2.13, 27.7, 32.5, B.3 Joints damp-proof course 21.4.1, 32.10 design arches 27.6 bonding 27.1 finish 21.3.1, 21.3.2.4, B.3, Figure 19 profile 21.3.1, 21.3.2.4 tooling 27.7 movement see Movement joints recessed 21.3.2.4, 27.7 types 2.2.4 workmanship bonding 32.1, 32.13 bricklaying 32.7 blocklaying 32.8 reinforced block lintels 32.9 size 32.2 tooling 32.5 Joist hangers design floors 19.1 roofs 19.2 protection against corrosion 22.7.1, Table 14 specification 8, Table 1 Lateral restraint 19.1, 19.2 Lateral restraint straps protection against corrosion 22.7.1, Table 14 specification 8, Table 1 Lightweight aggregates 6.3.2 Lime mix design 23.1, 23.2, Table 15, Table 17 specification 6.2 storage on site 30.3 workmanship 31 Lime : sand 6.6, 23.2.7, 30.5, 31.3, Table 17 Lime bloom 2.14, 22.1.3, 35.2 Lintels design bearings 19.3 cavity bridges 21.4.2 composite 19.3 concentrated loads 18.3 damp-proof systems 21.5.5, Figure 12(d) and Figure 12(e) pressed steel 19.3 protection against corrosion 22.7.1, Table 14 stop-ends 21.5.5 specification 14
104
workmanship bearings 32.1 general 33.4 reinforced block 32.9 wall ties 32.11.3 Loading 17.2 Local spell index 21.2, Table 10 see also Wind-driven rain index Manholes 3, 22.1.3, Table 13(L) Masonry definition 2.15 design 17 to 27 adhesion 17.5 constructional details 27 durability 22 architectural features 22.5 exposure to the weather 22.2 frost action 22.3 general 22.1 selection of masonry units 22.6, Table 13 selection of mortars 22.6, Table 13 sulphate attack 22.4 excslusion of moisture 21 classification of exposure to local wind-driven rain 21.2, Table 10 damp-proof systems 21.4 to 21.9 selection of external constructions 21.3 factors to be considered 17.1 fire resistance 24, Table 16 foundations 17.4 general 17 impact resistance 17.3 loading 17.2 mortars 23 movement 20, Appendix A accommodation 20.3 adjoining structural members 20.2 determination Appendix A general 20.1 reinforcement 20.5 sealing of movement joints 20.4 sound absorption and noise reduction 26 selection of masonry units and materials 17.6, Table 6 stability 18, 19 detailing 19 chimneys 19.7 floors 19.1 fittings 19.6 fixings 19.4 openings 19.3 roofs 19.2 services 19.6 wall ties 19.5
general 18 concentrated loads 18.3 imposed lateral load only 18.4 imposed vertical and lateral loads 18.2 internal walls 18.5 partitions not designed for imposed loading 18.5 materials 5, 6 workmanship 28 to 36 constructional details 33 laying of masonry units 32 mortars 31 protection against damage 35 scaffolding 29 services 34 setting out 28 storage on site 30 supervision 36 Masonry bond definition 2.16 design 17.1, 27.1 types Appendix B workmanship 32.1, 32.13 Masonry cement mix design 23.1, 23.2.4 specification 6.1 workmanship 31 Masonry paint effect on durability 22.1 effect on rain penetration 21.3.2.1, Table 11(B) Masonry units see also Bricks and Blocks definition 2.17 design adhesion 17.5 bonding 20.1, 27.1 durability 22.6, Table 13 frost attack 22.3 movement Appendix A selection 17.6, Table 6 sulphate attack 22.4 special shapes 32.13 specification 5.1 types 2.27 workmanship adhesion 32.3 appearance 32.4 laying 32.7, 32.8 protection during construction 35 setting out 32.1 storage on site 30.2 Materials 5 to 16 Mortars design adhesion 17.5 admixtures 23.3 durability 20.1, 22.6, Table 13 mixes 23.1, Table 15
© BSI 11-1999
BS 5628-3:1985
resistance to rain penetration 21.3.1, 21.3.2.3, 21.3.2.4 types 23.2.1 air-entrained (plasticized) 23.2.5 cement 23.2.2 cement : lime : sand 23.2.3 lime : sand 23.2.7 masonry cement 23.2.4 ready-to-use 23.2.6 specification 6 workmanship adhesion 32.3 appearance 32.4 batching 31.4, Table 17 and Table 18 jointing 32.5 mixing 31.4 pointing 32.6 protection during construction 35 storage on site 30.5 Movement 20 accommodation adjoining structural members 20.2 general 20.1 masonry 20.3 determination Appendix A effect on stability 18.1, 18.5 reinforcement 20.5 Movement joints see also Slip planes definition 2.24.4 design 20.3.1, 21.7 effect on stability 18.1, 20.2.3.2 fire resistance 24 provision 20.3.2 sealing 20.4 slips 20.2.4 types Figure 10 wall ties 19.5 workmanship 33.8 Noise reduction 26 Openings damp-proof courses 21.5.5, Figure 12(a), Figure 12(b), Figure 12(d) and Figure 12(e) movement joints 20.3.2.5 partitions 18.5 reinforcement 20.5 support over 19.3 wall ties 19.5 walls without edge restraint 18.4.2, Figure 2(b) Padstones 18.3, 19.2 Panels definition 2.18 design fire resistance 24
© BSI 11-1999
movement joints 20.2.3, 20.3.2 stability 18.4.2, Figure 2(b) Parapets damp-proof courses 21.5.7, Figure 12(g) durability 22.1.3, 22.4, 22.6, Table 13(F) and Table 13(G) movement 20.3.2.2 stability 18.4.1 Partitions design movement 20.2.2 stability 18.5 workmanship 33.7 Paved surrounds, effect on adjacent masonry 22.1 Perpend joints definition 2.24.5 design 21.4.6, 26.2.1 workmanship 32.4, 32.10.6 Piers definition 2.19 design movement 20.3.2.5 stability 18.1, 18.3 workmanship 33.2 Pigments see Colouring agents Pistol brick 2.26.3, 27.4 Plaster damp-proof courses 21.4.7 partitions 18.5 Plasticizers mix design 23.2.1, 23.2.5, Table 15 specification 6.4.3 workmanship 31.3 Pointing 2.20, 27.7, 32.6, B.3 Protection against corrosion 22.7, Table 14 Protection against damage during construction 35 Quoins 2.21, 27.1.3, 33.1 Rain penetration, resistance to design cavity insulation 21.3.2.8 factors affecting cavity walls 21.3, Table 11(B) general 21.1 selection of external constructions 21.3 thickness of single-leaf walls Table 11(A) workmanship 21.3.2.2, 32.5, 32.11 Recessed joints 21.3.2.4, 22.1.1, 27.7, 32.5, B.3 Reinforcement bed joint 20.2.1, 20.3.2.2 crack control 20.5 damp-proof courses 21.4.7 protection against corrosion
non-structural 22.7.1, Table 14 structural 22.7.2 specification 9 workmanship 32.7, 32.8, 32.10.1 Rendering design 21.3.2.1, 21.4.7, Table 11, 22.5 workmanship 32.5 Retaining walls 22.1.3, Table 13(L) Reveals 33.1 Roofs connections 19.1, Figure 7 stability 18.1 Saturation, risk of 22.1.1, 22.1.2, 22.1.3, 22.3.1, 22.5, Table 13, 35.2, 35.3 Scaffolding 29 Sealants design 20.4 specification 11 workmanship 33.8 Selection of masonry units and mortars durability 22.6, Table 13 general 17.6, Table 6 Services 19.6, 21.4.7, 27.9, 32.10.1, 34 Setting out 28, 32.1 Sewerage Table 13(L) Shell bedding 2.26, 21.3.2.5, 27.1.3, 32.8 Sills design damp-proof courses 21.5.3, Figure 12(a) and Figure 12(b) durability 22.1.3, 22.6, Table 13(J) effect on durability of masonry 22.1.1, 22.5 specification 13 workmanship 33.3 Simple support 2.33.2, Figure 5 Single-leaf walls see also Masonry and Walls definition 2.28.1 design area of walls with edge restraint 18.4.2.1 exclusion of moisture 21.3.2.5, Table 11(A) fire resistance 24, Table 16(A) and Table 16(B) free standing walls 18.4.1 sound insulation 26.2.1 support conditions 18.4.2.2 Sleeper walls 2.28.6, 19.1 Slips definition 2.26.4 design 20.2.4, 27.3 workmanship 32.12 Slip planes 18.1, 20.2.2, 20.3.1 Snap headers 2.26.5 Sound absorption 26.1 Sound insulation construction details 26.2.2 general 26.2.1
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BS 5628-3:1985
movement joints 20.3.1 wall ties Table 9(B) workmanship 32.7 Special masonry units 2.27.6, 32.13 Spreader beams 18.3, 19.2 Squints 2.26.7 Stability 18, 19 Stop-ends 21.4.5, 21.5.5, Figure 12 Storage on site 30 Stretchers 2.26.8, Figure 17 String courses 2.22, 27.2.1 Suction rate 17.5, 32.3 Sulphate attack 21.3.2.1, 22.1.2, 22.1.3, 22.4 Sulphate-resisting cement 6.1, 22.4, Table 13 Supervision 36 Support conditions 18.4.2.2 Supports 2.27, Figure 5 Temporary support during construction 18.1, 18.5, 32.9, 33.4, 33.5 Thermal insulation 21.3.2.8, 25.3 Thermal properties 25 Thresholds 21.5.6, 33.3 Throatings 21.7, 22.1.1, Figure 9
106
Timber, protection against corrosion 22.7.3 Toothing 2.23, 33.6, 33.7 Truss roofs, connections with straps Figure 7(d) without straps Figure 7(e) Veneering 27.2.4 Veneered walls 2.28.7, 27.2.5 Walls see also Masonry, Single-leaf walls and Cavity walls external becoming internal (d.p.c.s) 21.8, Figure 12(h) external flanking walls (sound insulation) 26.2.2.2 internal (stability) 18.5 separating (sound insulation) 26.2.2.1 subjected to concentrated loads 18.3 subjected to imposed loads 18.2 subjected to imposed lateral load only 18.4 types 2.28 with edge restraint 18.4.2
Wall plates 19.1, 19.2 Wall ties design general 19.5, Table 9 sound insulation 26.2.1 specification 7 workmanship 32.11 Water, quality of 6.5 Water repellents 21.3.2.1, Table 11(B) Weathering 2.29, 16, 21.6 Weepholes 21.4.6, 32.10.6 Wetting of masonry units 17.5, 32.3 Wind-driven rain index 21.1, 21.2 Windows see also Openings design effect on durability of masonry 22.5 exclusion of moisture 21.3.2.6, 21.5.4, Figure 12(c) placing of movement joints 20.3.2.3, 20.3.2.4 workmanship 33.9 Wind zones 18.4, Figure 1 Workmanship 21.3.2.2, 30 to 36
© BSI 11-1999
BS 5628-3:1985
Publications referred to BS 12, Specification for ordinary and rapid-hardening Portland cement. BS 146, Portland-blastfurnace cement. BS 146-2, Metric units. BS 187, Specification for calcium silicate (sandlime and flintlime) bricks. BS 402, Specification for clay plain roofing tiles and fittings. BS 473 & BS 550, Concrete roofing tiles and fittings. BS 476, Fire tests on building materials and structures. BS 476-8, Test methods and criteria for the fire resistance of elements of building construction. BS 493, Specification for airbricks and gratings for wall ventilation. BS 729, Hot dip galvanized coatings on iron and steel articles. BS 743, Materials for damp proof courses. Metric units. BS 747, Specification for roofing felts. BS 849, Plain sheet zinc roofing. BS 877, Formed or expanded blastfurnace slag lightweight aggregate for concrete. BS 877-2, Metric units. BS 882, Specification for aggregates from natural sources for concrete. BS 890, Building limes. BS 915, High alumina cement. BS 915-2, Metric units. BS 970, Specification for wrought steels for mechanical and allied engineering purposes. BS 970-1, General inspection and testing procedures and specific requirements for carbon, carbon manganese, alloy and stainless steels. BS 988, BS 1076, BS 1097, BS 1451, Mastic asphalt for building (limestone aggregate). BS 1014, Pigments for Portland cement and Portland cement products. BS 1047, Specification for air-cooled blastfurnace slag coarse aggregate for concrete. BS 1178, Specification for milled lead sheet and strip for building purposes. BS 1186, Quality of timber and workmanship in joinery. BS 1186-1, Quality of timber. BS 1186-2, Quality of workmanship. BS 1197, Concrete flooring tiles and fittings. BS 1198, BS 1199 and BS 1200, Building sands from natural sources. BS 1243, Specification for metal ties for cavity wall construction. BS 1286, Clay tiles for flooring. BS 1289, Precast concrete flue blocks for domestic gas appliances. BS 1449, Steel plate, sheet and strip. BS 1449-1, Specification for carbon and carbon manganese plate, sheet and strip. BS 1449-2, Stainless and heat resisting steel plate, sheet and strip. BS 1470, Wrought aluminium and aluminium alloys for general engineering purposes — plate, sheet and strip. BS 1554, Specification for stainless and heat-resisting steel round wire. BS 1881, Methods of testing concrete. BS 1881-5, Methods of testing hardened concrete for other than strength. BS 2870, Specification for rolled copper and copper alloys: sheet, strip and foil. BS 2873, Copper and copper alloys. Wire. BS 2874, Copper and copper alloys. Rods and sections (other than forging stock). BS 2989, Specification for continuously hot-dip zinc coated and iron-zinc alloy coated steel: wide strip, sheet/plate and slit wide strip. © BSI 11-1999
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BS 5628-3:1985 BS 3111, Specification for steel wire for cold forged fasteners and similar components. BS 3111-2, Stainless steel. BS 3148, Methods of test for water for making concrete (including notes on the suitability of the water). BS 3416, Black bitumen coating solutions for cold application. BS 3797, Specification for lightweight aggregates for concrete. BS 3797-2, Metric units. BS 3826, Silicone-based water repellents for masonry. BS 3921, Specification for clay bricks. BS 4027, Specification for sulphate-resisting Portland cement. BS 4254, Specification for two-part polysulphide-based sealants. BS 4360, Specification for weldable structural steels. BS 4721, Specification for ready-mixed building mortars. BS 4729, Shapes and dimensions of special bricks. BS 4887, Mortar plasticizers. BS 5215, One-part gun-grade polysulphide-based sealants. BS 5224, Specification for masonry cement. BS 5250, Code of basic data for the design of buildings: the control of condensation in dwellings. BS 5262, Code of practice for external rendered finishes. BS 5268, Code of practice for the structural use of timber. BS 5268-5, Preservative treatments for constructional timber. BS 5390, Code of practice for stone masonry. BS 5440, Code of practice for flues and air supply for gas appliances of rated input not exceeding 60 kW (1st and 2nd family gases). BS 5440-1, Flues. BS 5493, Code of practice for protective coating of iron and steel structures against corrosion. BS 5606, Code of practice for accuracy in building. BS 5618, Code of practice for the thermal insulation of cavity walls (with masonry inner and outer leaves) by filling with urea-formaldehyde (UF) foam. BS 5628, Code of practice for use of masonry. BS 5628-1, Structural use of unreinforced masonry. BS 5628-2, Structural use of reinforced and prestressed masonry. BS 5642, Sills and copings. BS 5642-1, Specification for window sills of precast concrete, cast stone, clayware, slate and natural stone. BS 5642-2, Specification for copings of precast concrete, cast stone, clayware, slate and natural stone. BS 5810, Code of practice for access for the disabled to buildings. BS 5838, Specification for dry packaged cementitious mixes. BS 5838-2, Prepacked mortar mixes. BS 5889, Specification for silicone based building sealants. BS 5896, Specification for high tensile steel wire strand for the prestressing of concrete. BS 5973, Code of practice for access and working scaffolds and special scaffold structures in steel. BS 5974, Code of practice for temporarily installed suspended scaffolds and access equipment. BS 5977, Lintels. BS 5977-2, Specification for prefabricated lintels. BS 6017, Specification for copper refinery shapes. BS 6073, Precast concrete masonry units. BS 6073-1, Specification for precast concrete masonry units. BS 6100, Glossary of building and civil engineering terms. BS 6100-5, Masonry. BS 6150, Code of practice for painting of buildings. BS 6178, Joist hangers. 108
© BSI 11-1999
BS 5628-3:1985 BS 6178-1, Specification for joist hangers for building into masonry walls of domestic dwellings. BS 6180, Code of practice for protective barriers in and about buildings. BS 6213, Guide to the selection of constructional sealants. BS 6232, Thermal insulation of cavity walls by filling with blown man-made mineral fibre. BS 6270, Code of practice for cleaning and surface repair of buildings. BS 6270-1, Natural stone, cast stone and clay and calcium silicate brick masonry. BS 6323, Specification for seamless and welded steel tubes for automobile, mechanical and general engineering purposes. BS 6398, Specification for bitumen damp-proof courses for masonry. BS 6399, Design loading for buildings. BS 6399-1, Code of practice for dead and imposed loads. BS 6457, Specification for reconstructed stone masonry units. BS 6461, Installation of chimneys and flues for domestic appliances burning solid fuels (including wood and peat). BS 6510, Specification for steel windows, windowboards and doors. BS 6515, Specification for polyethylene damp-proof courses for masonry. BS 6577, Specification for mastic asphalt for building (natural rock asphalt aggregate). BS 6649, Specification for clay and calcium silicate modular bricks. BS 8301, Code of practice for building drainage. CP 3, Code of basic data for the design of buildings. CP 3:Chapter V, Loading. CP 3-2, Wind loads. CP 101, Foundations and substructures for non-industrial buildings of not more than four storeys. CP 102, Protection of buildings against water from the ground. CP 143, Sheet roof and wall coverings. CP 143-16, Semi-rigid asbestos bitumen sheet. Metric units. CP 144, Roof coverings. CP 144-3, Built-up bitumen felt. CP 2004, Foundations. CP 2005, Sewerage. DD 93, Methods for assessing exposure to wind-driven rain. CIBS Guide Section A3 Thermal properties of building structures9). BCRA Special Publication No. 56 Model Specification for Load-bearing Clay Brickwork10). BRE Report Driving Rain Index11). BRE Digest 176 Failure patterns and implications11). BRE Digest 236 Cavity insulation11).
9) Published by the Chartered Institution of Building Services. 10) Published by the British Ceramic Research Association. 11)
Published by the Building Research Establishment.
© BSI 11-1999
BS 5628-3: 1985
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