British Standard
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BRITISH STANDARD
Specification for
Gypsum building plasters — Part 1: Excluding premixed lightweight plasters
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UDC 691.55:666.91
BS 1191-1: 1973
BS 1191-1:1973
Co-operating organizations The Cement, Lime and Gypsum Industry Standards Committee, under whose supervision this British Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations: Association of Consulting Engineers British Steel Industry British Precast Concrete Federation British Railways Board British Ready Mixed Concrete Association British Quarrying and Slag Federation Cement and Concrete Association Cement Makers’ Federation* Chemical Industries Association*
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Concrete Society Department of the Environment* Department of the Environment — Building Research Establishment* Federation of Civil Engineering Contractors Greater London Council Gypsum Products Development Association* Imperial Chemical Industries Limited Institution of Civil Engineers Institution of Municipal Engineers* Institution of Structural Engineers Institution of Water Engineers National Federation of Building Trades Employers* Sand and Gravel Association Limited Society of Chemical Industry* The Royal Institution of Chartered Surveyors* Welwyn Hall Research Association
This British Standard, having been approved by the Cement, Lime and Gypsum Industry Standards Committee, was published under the authority of the Executive Board on 5 October 1973 © BSI 03-1999 First published as BS 1191, December 1944 First revision November 1955 Second revision as BS 1191-1, August 1967 Third revision October 1973
The following BSI references relate to the work on this standard: Committee reference CEB/15
ISBN 0 580 07690 3
The Government departments and scientific and industrial organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this British Standard: British Gypsum Limited Modular Society National Federation of Plastering Contractors Royal Institute of British Architects Individual manufacturers
Amendments issued since publication Amd. No.
Date of issue
Comments
BS 1191-1:1973
Contents
Co-operating organizations Foreword 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 2 2.1 2.2 2.3 2.4
Page Inside front cover ii
General Scope Definitions Classification Purity Composition Marking Samples for testing and sampling Manufacturer’s certificate Quality of the different classes Class A. Plaster of paris Class B. Retarded hemihydrate gypsum plaster Class C. Anhydrous gypsum plaster Class D. Keene’s plaster
1 1 1 1 1 1 1 1 2 2 2 3 3
Appendix A Determination of chemical composition and loss on ignition Appendix B Examination for soundness Appendix C Method of determining transverse strength Appendix D Determination of mechanical resistance by the dropping ball test Appendix E Determination of expansion Appendix F Method of stabilizing classes A and B plast ers Appendix G Determination of freedom from coarse particles Appendix H Examples of typical classification markings required by 1.6
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Figure 1 — Gang mould Figure 2 — Extensometer Publication referred to
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4 4 4 6 7 8 8 8 9 11
Inside back cover
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BS 1191-1:1973
Foreword This British Standard has been revised under the authority of the Cement, Lime and Gypsum Industry Standards Committee to bring it into line with current practice. The terms used to describe the function and types of plaster accord with those given in BS 4049, “Glossary of terms applicable to i nternal plastering, external rendering and floor screeding ”. The alphabetical classification of the plasters remains unchanged but the Class B category in this edition is restricted to undercoat and final coat plasters and their sub-divisions, while plasters in Classes C and D are for finishing purposes only. Improvements have been made to a number of test procedures and additional test methods have been introduced. This has led to the modification of certain performance requirements. In accordance with the change to the metric system this standard has now been metricated giving values in terms of SI units. For furth er information on SI units reference should be made to BS 3763, “The International System of units (SI)”. Figure 1 and 1.8 have been amended and Figure 2 deleted, but otherwise the contents are the same as the previous edition which it is proposed to withdraw when this standard is published. NOTE
1 N/mm2 = 1 MN/m2 = 1 MPa.
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.
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Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 12, 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. ii
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BS 1191-1:1973
1 General
1.3 Classification
1.1 Scope
Gypsum plaster shall be of one of the following classes:
This British Standard specifies requirements for those plasters which have a definite set due to the hydration of calcium sulphate to form gypsum and which are intended for general building operations and for the manufacture of preformed building products. Premixed lightweight building plasters are not included in this Part of the standard (see Foreword). NOTE The British Standards referred to in this standard are listed on the inside back cover.
1.2 Definitions For the purposes of this British Standard, the following definitions apply: gypsum the dihydrate of calcium sulphate, CaSO 4.2H2O, is the raw material from which the gypsum plasters are commonly manufactured; it is also the final stage in the setting of gypsum plasters
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Class A. Plaster of Paris Class B. Retarded hemihydrate gypsum plaster Class C. Anhydrous gypsum plaster Class D. Keene’s plaster
1.4 Purity No materials shall be added to gypsum plasters except such as are necessary to control the setting and working characteristics or to impart anti-corrosion or fungicidal properties.
1.5 Composition Gypsum plaster shall comply with the relevant clause on chemical composition in Section 2. Materials present arising from impurities in the original gypsum used in manufacture, or from permissible additions under 1.4 shall not be of a type having deleterious effects on the set plaster.
hemihydrate
1.6 Marking
an intermediate phase in the dehydration of gypsum by heat wherein the amount of combined water corresponds approximately to the formula 2CaSO4.H2O, calcium sulphate hemihydrate. The formula is often written CaSO4.½H2O, hence the designation hemihydrate
The vendor shall show clearly on each package of plaster the number of this British Standard, i.e. BS 1191-1, the class and type to which the plaster belongs (see Appendix H for examples) and the date of manufacture. In addition, it shall be clearly indicated whether the plaster is to be used as an undercoat or final coat.
plaster of paris
NOTE Attention is drawn to certification facilities offered by BSI: see the inside back cover of this standard.
a form of hemihydrate without any added retarder of set. It is manufactured in several grades for various industrial uses retarded hemihydrate a form of hemihydrate which contains an addition of a retarder of set anhydrous gypsum plaster a material consisting essentially of anhydrous calcium sulphate (CaSO4), produced by the dehydration of gypsum, the set of which has been suitably accelerated keene’s plaster a gypsum plaster of the anhydrous class which is characterized by being more easily brought to a smooth and true finish in continuous plastered surface, this property being associated as well with a gradual set
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1.7 Samples for testing and sampling Each sample shall be not less than 5 kg in weight, and shall be enclosed immediately in a clean, dry, airtight container. The process of sampling shall be carried out in as short a time as possible. Sufficient material shall be taken in approximat ely equal portions selected from at least twelve different positions when the plaster is loose, from not less than twelve different packages when the plaster is not loose, or, where there are fewer than twelve different packages, from each package. The portions shall be thoroughly mixed and shall be quartered down to give a sample of the weight required for testing. Every care shall be taken in the selection so that a fair, average sample is obtained. The vendor shall afford every facility for the efficient sampling of the bulk and for subsequently identifying the plaster sampled.
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1.8 Manufacturer’s certificate At the purchaser’s request the supplier shall provide statistical quality control certificates, or a certificate stating that the product complies with the requirements of this British Standard.
2 Quality of the different classes 2.1 Class A. Plaster of paris 2.1.1 Compliance with tests. Plaster of Paris shall comply with the requirements of 2.1.2 to 2.1.5 when tested by the methods described in the relevant Appendix A to Appendix G. 2.1.2 Chemical composition. The chemical compositions shall be as follows when determined as described in Appendix A: 1) The sulphur trioxide content, expressed as a percentage by weight of the plaster as received, shall be not less than 35 %. 2) The calcium oxide content shall be not less than two-thirds of the sulphur trioxide content, by weight. 3) The sum of the soluble sodium salt and magnesium salt contents, expressed as percentages of sodium oxide (Na 2O), and magnesium oxide (MgO), by weight of the plaster as received, shall be not greater than 0.2 %.
I S B ) 4) The loss on ignition shall be not greater c ( than 9 % and not less than 4 % by weight of the , y plaster as received. p o 2.1.3 Freedom from coarse particles. The C d residue on a 1.18 mm sieve complying with the e l l requirements of BS 410 shall be not greater o than 5 % by weight when determined by the method r t n described in Appendix G. o c 2.1.4 Soundness. The set plaster pats shall show n U no signs of disintegration, popping or pitting when , examined by the method described in Appendix B. 1 0 2.1.5 Transverse strength. The transverse 0 2 strength (modulus of rupture) of set plaster shall be , 2 2 not less than 2.5 N/mm when determined in 2 accordance with the method described in y l u Appendix C. J , n 2.2 Class B. Retarded hemihydrate a h gypsum plaster c n 2.2.1 Type. Retarded hemihydrate gypsum plasters a h shall be of one of the following types: c : Type a: Undercoat plaster (plaster for use with y sand) p o 1. Browning plaster C d 2. Metal lathing plaster e s n e c i L
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Type b: Final coat plaster 1. Finish plaster 2. Board finish plaster 2.2.2 Compliance with tests. When tested by the methods described in Appendix A to Appendix G, retarded hemihydrate plasters shall comply with the requirements of 2.2.3 and 2.2.5. In addition, the following plasters shall comply with the subclauses indicated: 1) Browning plaster Type a. 1:
2.2.6
2) Metal lathing plaster, Type a. 2:
2.2.3 5) and 2.2.6
3) Finish plaster, Type b. 1:
2.2.4 and 2.2.7
4) Board finish plaster, Type b. 2:
2.2.4, 2.2.7 and 2.2.8
2.2.3 Chemical composition. The chemical composition shall be as follows when determined as described in Appendix A: 1) The sulphur trioxide content, expressed as a percentage by weight of the plaster as received, shall be not less than 35 %. 2) The calcium oxide content shall be not less than two-thirds of the content of sulphur trioxide by weight. 3) The sum of the soluble salt and magnesium salt contents, expressed as percentages of sodium oxide (Na2O), and magnesium oxide (MgO), by weight of the plaster as received, shall be not greater than 0.2 %. 4) The loss on ignition shall be not greater than 9 % and not less than 4 % by weight of the plaster as received. 5) For metal lathing plaster, the free lime shall be not less than 3 % by weight at the time of despatch. 2.2.4 Freedom from coarse particles. The residue on a 1.18 mm sieve complying with the requirements of BS 410 shall be not greater than 1 % by weight when determined by the method described in Appendix G. 2.2.5 Soundness. The set plaster pats shall show no signs of disintegration, popping or pitting when examined by the method described in Appendix B. 2.2.6 Transverse strength. The transverse strength (modulus of rupture) of the set sanded plaster shall be not less than 1.2 N/mm2 when tested in accordance with the method described in Appendix C.
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2.2.7 Mechanical resistance. The mechanical resistance of the set neat plaster shall be such that the impact of the dropping ball produces an indentation having a diameter not greater than 5 mm when determined as described in Appendix D. 2.2.8 Expansion on setting. The linear expansion on setting at the time of despatch shall not exceed 0.2 % in one day when tested in accordance with the method described in Appendix E.
2.3 Class C. Anhydrous gypsum plaster 2.3.1 Type. Anhydrous gypsum plasters are for finishing only. 2.3.2 Compliance with tests. Anhydrous gypsum plasters shall comply with the requirements of 2.3.3 to 2.3.6. 2.3.3 Chemical composition. The chemical composition shall be as follows when determined as described in Appendix A: 1) The sulphur trioxide content, expressed as a percentage by weight of the plaster as received, shall be not less than 40 %.
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2) The calcium oxide content shall be not less than two-thirds of the sulphur trioxide content b y weight. 3) The sum of the soluble sodium salt and magnesium salt contents, expressed as percentages of sodium oxide (Na2O), and magnesium oxide (MgO), by weight of the plaster as received, shall be not greater than 0.2 %. 4) The loss on ignition shall be not greater than 3 % by weight of the plaster as received. 2.3.4 Freedom from coarse particles. The residue on a 1.18 mm sieve complying with the requirements of BS 410 shall be not greater than 1 % by weight when determined as described in Appendix G. 2.3.5 Soundness. The set plaster pats shall show no signs of disintegration, popping or pitting when examined by the method described in Appendix B. 2.3.6 Mechanical resistance. The mechanical resistance of the set neat plaster shall be such that the impact of the dropping ball produces an indentation having a diameter not greater than 4.5 mm when determined as described in Appendix D.
2.4 Class D. Keene’s plaster 2.4.1 Type. Keene’s plaster is for finishing only.
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NOTE Keene’s plaster is of the anhydrous type. It is characterized by being more easily brought to a smooth and clean finish associated with gradual set. In this British Standard, Keene’s plaster is differentiated from a Class C gypsum plaster by a higher standard of purity and hardness. The special qualities traditionally associated with this type of plaster cannot be dealt with at present by any convenient direct test.
2.4.2 Compliance with tests. The plaster shall comply with the requirements of 2.4.3 to 2.4.6. 2.4.3 Chemical composition. The chemical composition shall be as follows, when determined as described in Appendix A: 1) The sulphur trioxide content, expressed as a percentage by weight of the plaster as received, shall be not less than 47 %. 2) The calcium oxide content shall be not less than two-thirds of the sulphur trioxide content by weight. 3) The sum of the soluble sodium salt and magnesium salt contents expressed as percentages of sodium oxide (Na2O), and magnesium oxide (MgO), by weight of the plaster as received, shall be not greater than 0.2 %. 4) The loss on ignition shall be not greater than 2 % by weight of the plaster as received. 2.4.4 Freedom from coarse particles. The residue on a 1.18 mm sieve complying with the requirements of BS 410 shall be not greater than 1 % by weight when determined as described in Appendix G. 2.4.5 Soundness. The set plaster shall show no signs of disintegration, popping or pitting when examined by the method described in Appendix B. 2.4.6 Mechanical resistance. The mechanical resistance of the set neat plaster shall be such that the impact of the dropping ball produces an indentation having a diameter not greater than 4 mm when determined as described in Appendix D. 2.4.7 Testing conditions 2.4.7.1 Temperature. Unless otherwise specified, the temperature of the materials, including water, and that of the test room at the time when the tests are being performed shall be 20 ± 5 °C. Plaster intended for use in hot climates may be tested at any higher temperature up to 35 °C when agreed upon between the purchaser and the vendor, and shall then comply with the requirements of this British Standard. 2.4.7.2 Reagents. All reagents shall be of analytical reagent quality. The water to be used in all testing operations shall be distilled or deionized, and unless otherwise stated, between the limits of temperature indicated in 2.4.7.1.
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Appendix A Determination of chemical composition and loss on ignition A.1 Determination of sulphur trioxide and calcium oxide. Mix 1 g of the plaster, ground to pass a 212 4 m sieve complying with the requirements of BS 410, with 100 ml of water in a beaker; add 5 g of powdered ammonium carbonate, heat the whole to boiling and simmer gently for 30 minutes. Boil the liquid until the greater part of the excess of ammonium carbonate is removed. Neutralize the soluble with 2N hydrochloric acid (methyl red indicator), add an excess of 20 ml of the acid and continue boiling for a further 10 minutes. Filter off the insoluble matter, thoroughly wash the residue with hot water and dilute the combined filtrate and washings to 250 ml. Determine the sulphur trioxide and calcium oxide contents in this filtrate. A.2 Determination of soluble sodium and magnesium salts. Weigh 1 g of the plaster, ground to pass a 212 4 m sieve complying with the requirements of BS 410 into a polythene bottle, add 100 ml of water at room temperature and 1 g of salt-free gypsum. Shake the bottle occasionally during the next hour to prevent caking and then allow it to stand until a clear supernatant liquid is obtained. Determine the contents of soluble sodium salts and magnesium salts in portions of the clear supernatant liquid. Express the results as Na2O and MgO. A.3 Determination of loss on ignition. Weigh 2 g of the plaster into a squat weighing bottle, previously weighed complete with cover. Distribute the plaster evenly over the bottle to constant weight at a temperature between 280 °C and 300 °C. Cover the weighing bottle and re-weigh immediately it is cool. A.4 Determination of free lime. Suspend 5 g of the sample in approximately 100 ml of water. Add several drops of phenolphthalein indicator solution (0.5 % in 50 % aqueous ethanol) and titrate with 0.5N hydrochloric acid until the pink colour of the indicator j ust disappears. Continue the tit ration until the pink colour does not return after standing for 2-3 minutes. With 5 g sample, 1 ml 0.5N acid
≡
0.37 % Ca(OH)2.
I Appendix B Examination for soundness S B ) Examine soundness by steaming six pats of neat plaster prepared as follows in ring moulds. The moulds c should be about 100 mm in diameter and 6 mm deep, well-greased before use and resting on well-greased ( , y non-porous base-plates. p o Gauge the Class A plaster with the appropriate amount of water to produce a smooth cream, and Classes B C to D with the appropriate amount of water to produce a stiff plastic paste convenient for filling the moulds. d Form the flat pats by pouring or pressing the material into the moulds in such a manner as to avoid e l l air-bubbles, and smooth off level with the top edge of the ring with a broad flexible palette-knife or the like. o r t Allow six pats to set undisturbed in air of at least 80 % relatively humidity for between 16 hours n o and 24 hours in the case of Classes A and B, and for three days in the case of Classes C and D, then subject c n them to the action of saturated steam at atmospheric pressure for a period of 3 hours, without removing U from the moulds, with the apparatus arranged so that condensed water cannot drip back on to the face of , 1 the pats. Visually examine the pats in a good light for signs of disintegration, popping or pitting. 0 0 2 Appendix C Method of determining transverse strength , 2 2 C.1 Apparatus. The following apparatus is required. y l 1) Moulds. A six-compartmented metal mould for making specimens 100 mm × 25 mm × 25 mm u J (see Figure 1). The 25 mm dimensions of the mould shall be accurate within ± 0.05 mm when new and , maintained within ± 0.1 mm. The internal faces of the mould sides shall be maintained plane n a to 0.01 mm over any 25 mm length and 0.04 mm overall. The mould shall be provided with a rectangular h c metal or glass plate 230 mm × 150 mm × 6 mm thick, and sufficiently plane to make, when greased, a n watertight joint with the sides of the mould, to act as a base. a h 2) Damp closet. The atmosphere of the damp closet for the storage of specimens shall be maintained at c : a relative humidity of at least 90 % at a temperature of 20 ± 5 °C. y p 3) Testing machine. An ordinary tensile strength cement-testing machine can readily be adapted for this o C transverse test by fitting appropriate clamps and adjusting the rate of loading. d e s n e c i L
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C.2 Standard sand. The standard sand shall be obtained from Leighton Buzzard, shall be of the white variety and shall be thoroughly washed and dried. Its loss of weight on extraction with hot hydrochloric acid shall be not more than 0.25 % when tested as follows: Dry the sand at 100 °C for one hour, weigh 2 g into a porcelain dish, add 20 ml of hydrochloric acid of relative density 1.16 and 20 ml of distilled water. Heat on a water bath for one hour, wash well with hot water, dry, and ignite in a covered crucible. The sand shall all pass through an 850 4 m sieve and not more than 10 % by weight shall pass a 600 4 m sieve. Both sieves shall comply with the requirements of BS 410. C.3 Preparation of test specimens C.3.1 Class A plaster. Stabilize the plaster in accordance with the method given in Appendix F. Prepare the six specimens as follows using a mix of neat plaster at a standard pourable consistence determined in advance as described below: Sprinkle the plaster (a convenient quantity is 450 g) over the surface of the required amount of water over a period of 30 seconds. Allow to stand for 30 seconds and then stir for 60 seconds, after which time the mix shall be of uniform consistence throughout. Immediately pour the mix into the moulds and vibrate the moulds by hand to remove air bubbles. Remove excess material, leaving slightly more than needed to fill the mould. The whole operation should be completed as soon as possible after the mixing. Allow the specimens to remain undisturbed in the moulds for 24 hours, under a damp cloth or in a damp closet. Scrape the top surface of the prisms smooth and level with the top of the mould. Remove the prisms from the mould, dry to constant weight in a well-ventilated oven maintained at a temperature between 35 °C and 40 °C and test dry. C.3.1.1 Standard pourable consistence. The apparatus consists of a hollow corrosion-resistant metal cylinder of internal diameter 30 mm and height 50 mm with the ends square to the longitudinal axis. It is centred on a metal baseplate. I S B ) c ( , y p o C d e l l o r t n o c n U , 1 0 0 2 , 2 2 y l u J , n a h c n a h c : y p o C d e s n e c i L
Over a period of 30 seconds sprinkle 100 g of the plaster over the surface of a known volume of water in which 0.1 g of sodium citrate has previously been dissolved. Allow to stand for 30 seconds and then stir for 60 seconds. Transfer the mixture to the metal cylinder and strike off level with the top. Thirty seconds after mixing is completed, lift the cylinder vertically1) and allow the mixture to spread over the baseplate. Measure the maximum and minimum diameters of spread and record the mean. Repeat the procedure varying the ratio of plaster to water until a mixture of standard pourable consistence is obtained. Record the plaster-water ratio. The standard pourable consistence corresponds to a mean diameter of spread of 78–80 mm. C.3.2 Class B undercoat plaster. Stabilize the plaster in accordance with the method given in Appendix F. Prepare six specimens with a mix of one part plaster and three parts standard sand by weight gauged with water to standard undercoat consistence as follows. A convenient quantity of plaster to use is 200 g. Mix the plaster with three times its weight of standard sand (see C.2) for two minutes and gauge with water to produce a paste of the standard undercoat consistence defined below. Determine the precise amount of water needed by previous trial. (As a guide, first try between 14 % and 17 % of the total dry weight, i.e. between 112 ml and 136 ml.) Add the dry sanded mix to the water over a period of 30 seconds and allow to soak for a further 30 seconds. Mix vigorously for one minute with a stiff-bladed spatula to produce a paste of uniform consistence. Test the mix for consistence as described in C.3.2.1. If the consistence is correct, fill the mix immediately into the appropriate moulds; if it is not correct repeat the whole procedure using a different proportion of water. Fill the mould to half height and consolidate the mix by tamping ten times with a 6 mm square brass rod along the length of the mould. Fill the mould above the top and consolidate the top layer in a similar manner. 1)
Mechanical devices may be used to control the rate of separation and to ensure that the cylinder is removed vertically. Alternatively, the cylinder may be clamped and the baseplate lowered.
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Allow the specimens to remain undisturbed in the moulds for 24 hours under a damp cloth or in a damp closet. Scrape the top surface of the plaster prisms smooth and level with the top of the mould. Remove the prisms from the mould, dry to constant weight in a well-ventilated oven maintained at a temperature between 35 °C and 40 °C and test dry. C.3.2.1 Standard consistence. Determine the standard testing consistence by means of a dropping ball penetrometer test as follows. Fill a ring mould identical with that specified in BS 4551 with the paste under test. Rest the mould on a non-porous plate, fill it by using a flexible palette-knife in about ten increments in such a manner as to eliminate voids or air-bubbles. Smooth off the surface of the paste level with the top of the mould. Drop a 25 mm diameter methylmethacrylate ball of weight 9.8 ± 0.1 g from rest from a height of 250 mm measured from the bottom of the ball to the surface of the paste, so that it falls approximately into the centre of the ring. Record the penetration as the distance from the lowest point of the ball to the level of the original surface of the material. Measure the depth of penetration by a suitable method, for example, as given in BS 4551. The paste is of the correct consistence when the ball penetrates 9-10 mm. C.4 Transverse strength test. Test each of six specimens 25 mm square in cross section and 100 mm long. Place the specimen under test symmetrically on two parallel metal rollers 10 mm in diameter and located at 75 mm centres. Apply the load by a third parallel roller of the same size at a point midway between the other two. Do not use any packing between the rollers and the specimen, and place the specimen so that the faces in contact with the rollers are those which were cast against the sides of the mould. Apply the load steadily and uniformly from zero, at a rate of not less th an 200 N/min and not more than 800 N/min. C.5 Calculation of results. Calculate the mean value of the breaking load of the six specimens and convert it to a modulus of rupture expressed in N/mm2. For the test conditions given, the value of the modulus is 0.0072 times the value of the mean breaking load in newtons.
I S B ) Appendix D Determination of mechanical resistance by the dropping ball test c ( , y D.1 Apparatus. The following apparatus is required. p 1) Moulds. As described in C.1 1). o C 2) Damp closet. As described in C.1 2). d e 3) Hard steel ball. 12.7 mm in diameter and weighing 8.33 g (ball bearing). l l o 4) Tube. Straight, smooth, clean and dry, approximately 16 mm in internal diameter and 1.72 m length. r t n o D.2 Preparation of test specimens c n D.2.1 Class B final coat plaster. Stabilize the plaster before test in accordance with the method described U in Appendix F. Prepare four test specimens as follows. , 1 A convenient quantity of plaster to use is 400 g. Add this over a period of 30 seconds to the appropriate 0 0 amount of water to produce a standard final coat consistence, allow to soak for one minute and then 2 mix with a stiff-bladed spatula for two minutes, after which time the mix shall be less uniform. , 2 2 Determine the precise amount of water needed by a previous trial. The determination of the required y l standard final coat consistence is described later. u J Fill the moulds in two layers, tamping each layer ten times with a 6 mm square brass rod along the , n length of the mould. Strike off the surface level with the top of the mould. a h Ensure that the specimens remain undisturbed in the moulds for 24 hours under a damp cloth or in a c damp closet and then remove them from the moulds. Finally, dry them to constant weight in a n a well-ventilated drying oven maintained at a temperature between 35 °C and 40 °C and test dry. h c D.2.2 Class C and D plasters. Prepare four test specimens as follows. : y A convenient quantity of plaster to use is 400 g. Add this over a period of 30 seconds to the appropriate p o amount of water to produce a standard final coat consistence. Stir the mix with a stiff-bladed spatula C for 30 seconds in the case of Class C plaster and for 60 seconds in the case of Class D plaster. d e s n e c i L
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Fill the moulds in two layers, tamping each layer ten times with a 6 mm square brass rod along the length of the mould. Strike off the surface level with the top of the mould. Ensure that the specimens remain undisturbed in the moulds for 24 hours under a damp cloth or in a damp closet and then remove them from the mould s. Store them in a damp closet for three d ays. Finally, dry them to constant weight in a well-ventilated drying oven maintained at a temperature between 35 °C and 40 °C and test dry. D.3 Standard consistence. Determine the standard final coat consistence by means of a dropping ball penetrometer precisely as described in C.3.2, except that the correct consistence in the present test corresponds to a penetration of 15-16 mm. When early stiffening occurs, 0.1 g of sodium citrate may be added to the gauging water for the determination of consistence. D.4 Mechanical resistance test procedure. Determine the resistance of the plaster to the impact of a falling ball by measuring the diameter of the impression produced on the smooth surface (which was in contact with the internal face of the mould when casting) of four neat plaster rods 25 mm square in cross section and 100 mm long, prepared, stored and dried as described in D.2, when a hard steel ball 12.7 mm in diameter and weighing 8.33 g (ball bearing) is allowed to fall freely from rest from a height of 1.82 m onto the horizontal surface of the plaster. After cleaning and polishing the hard steel ball, release it from rest down a straight, smooth, clean and dry tube approximately 16 mm in internal diameter and 1.72 m in length, supported firmly in a vertical position with the top of the specimen 100 mm below the bottom of the tube. Support the specimen under test firmly on a smooth, substantial and unyielding horizontal surface. Make eight impressions in all, one on each of the opposite faces of the four rods, avoiding blemishes and air-bubbles, and not more than 6 mm from the centre line or within 12 mm of the ends of the rod, measuring two diameters at right angles for each impression. Neglect any impression obviously irregular in shape and repeat the test on that face. Record the mean of the sixteen measurements. I S B ) c ( , y p o C d e l l o r t n o c n U , 1 0 0 2 , 2 2 y l u J , n a h c n a h c : y p o C d e s n e c i L
Appendix E Determination of expansion E.1 General. Determine the linear expansion on setting in continuous damp air storage by means of a simple extensometer described in E.2 with the neat plaster gauged to a standard final coat consistence. Stabilize the plaster before test by the method described in Appendix F. E.2 Extensometer. The extensometer has an open V-shaped cradle closed at one end by a fixed plate and at the other by a movable partition carried on the stem of an ordinary watch-pattern dial micrometer gauge of the Ames type reading to 1/100 mm (see Figure 2). The cradle is of brass or bronze 100 mm long, about 60 mm wide and 25 mm deep with a rounded bottom. The take-up or returning spring shall be light and the movement free. To prevent the plaster sticking to the sides of the cradle, grease before use and line internally with thin non-absorbent paper having a glazed surface. Renew th e paper lining for each test. Fill the gauged plaster into the cradle while the movable plate is held against the end, and strike off smooth and level with the top of the cradle. E.3 Zero adjustment. Move the movable partition very slightly forward clear of the end to eliminate backlash. Bring the plaster solid against the movable partition. Make any necessary zero adjustment on the dial. E.4 Gauging and measurement. A convenient quantity of plaster to use is about 200 g. Gauge this with water in the manner and to the standard final coat consistence described in D.2.3. Fill the gauged plaster immediately into the cradle of the extensometer and adjust the zero point as described in E.3. Place the extensometer in the damp closet and note the zero reading. Leave it undisturbed for 24 hours and then take the final reading. Calculate the percentage linear expansion. difference in dial readings in 1/100 mm Per cent linear expansion = -------------------------------------------------------------------------------------------------------------100
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Appendix F Method of stabilizing classes A and B plasters Stabilize these plasters before use in the tests for transverse strength, mechanical resistance and expansion on setting. For this purpose, expose the plaster for 3–4 days in a layer not more than 12 mm in thickness to an atmosphere of 65 ± 3 % relative humidity at a temperature of 20 ± 5 °C with vigorous air circulation over the specimen throughout this period. If a conditioned room is not available, maintain the humidity by means of a saturated solution of ammonium nitrate contained together with the solid salt in a wide dish, and placed in a tightly-closed cabinet. Keep the air in the cabinet moving over both solution and plaster.
Appendix G Determination of freedom from coarse particles Sift 100 g of plaster continuously for 5 minutes on a 1.18 mm sieve complying with the requirements of BS 410 and weigh the residue on the sieve. Break down air-set lumps in the sample with the fingers, without rubbing on the sieve.
Appendix H Examples of typical classification markings required by 1.6 Generic description
Marking
Retarded hemihydrate gypsum metal lathing plaster
BS 1191-1 CLASS B Type a. 2
Retarded hemihydrate gypsum board finish plaster
BS 1191-1 CLASS B Type b. 2
I S Anhydrous gypsum finish plaster B ) c Keene’s gypsum finish plaster ( , y p o C d e l l o r t n o c n U , 1 0 0 2 , 2 2 y l u J , n a h c n a h c : y p o C d e s n e c i L
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BS 1191-1 CLASS C BS 1191-1 CLASS D
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I S B ) c ( , y p o C d e l l o r t n o c n U , 1 0 0 2 , 2 2 y l u J , n a h c n a h c : y p o C d e s n e c i L
Figure 1 — Gang mould ( a) Plan view of mould (cover plate removed)
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I S B ) c ( , y p o C d e l l o r t n o c n U , 1 0 0 2 , 2 2 y l u J , n a h c n a h c : y p o C d e s n e c i L
Figure 1 — Gang mould ( a) Plan view of mould (cover plate removed) (continued)
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Figure 2 — Extensometer (see Appendix E) I S B ) c ( , y p o C d e l l o r t n o c n U , 1 0 0 2 , 2 2 y l u J , n a h c n a h c : y p o C d e s n e c i L © BSI 03-1999
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I S B ) c ( , y p o C d e l l o r t n o c n U , 1 0 0 2 , 2 2 y l u J , n a h c n a h c : y p o C d e s n e c i L
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Publications referred to This standard makes reference to the following British Standards: BS 410, Test sieves. BS 4551, Methods of testing mortar and specification for mortar testing sand.
I S B ) c ( , y p o C d e l l o r t n o c n U , 1 0 0 2 , 2 2 y l u J , n a h c n a h c : y p o C d e s n e c i L © BSI 03-1999
I S B ) c ( , y p o C d e l l o r t n o c n U , 1 0 0 2 , 2 2 y l u J , n a h c n a h c : y p o C d e s n e c i L
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