No. 19
Market & Technology for Professional Tilers
Trouble-free Laying and Grouting of Natural and Engineered Stones Natural stone surfaces have become increasingly popular. Ceramics now account for about 80 % and natural stone slabs for about 20 % of the “hard” surfacing sector. It is reported that about 4,000 to 5,000 different natural stones are available on the German market alone. However, experts in the field know that this figure is too high as a result of the fact that some natural stones are sold under up to 20 different brand names (e.g. Blue Pearl, Labrador Blue, Marina Pearl, Perla Azurro, ...). The following paragraphs are intended to help prevent errors in the laying of natural stones.
1. Origin of natural stones The 3,000 or more types of stone can be classified as igneous, sedimentary and metamorphic rocks depending on their origin. Dr. Josef Felixberger, Head of Technical Service, PCI Augsburg GmbH, deals with the subject of: "Trouble-free Laying and Grouting of Natural and Engineered Stones".
Igneous rocks (magmatic rocks or magmatites) are created by the solidification of molten rock. Solidification may take place over millions of years at great depth or within a few hours in the earth's crust. In the first case, we refer to plutonic, in the second to volcanic rocks. Plutonic rocks are characterized by low porosity and irregular, coarse-grained structures.
Our Advice! No. 19
Typical plutonic rocks include granite (e.g. Sardo Bianco) and gabbro (e.g. Nero Impala) as well as the acid-sensitive Azul da Bahia. In contrast to plutonic rocks, volcanic rocks may be highly porous. Typical volcanic rocks include basalt, trachyte and porphyry. Sedimentary rocks may be created either by erosion and transport from existing rocks by wind and water or by the chemical or biological precipitation of lime from bodies of water. Limestones are a special case in the group of sedimentary rocks as they contain vegetable and animal matter as well as free lime and are therefore prone to discoloration and efflorescence. Typical limestones include "Jura marble" and Solnhofen tiles. In addition to the limestones, sandstones and sandy shale also play an important role. As regards adhesion, there are few problems with laying sedimentary stones, as they are relatively porous.
Bianco Sardo (plutonic, granite) The minerals feldspar, quartz and mica are clearly visible. Traces of minerals containing iron (biotite) may lead to a yellow discoloration.
Metamorphic rocks are the third group of natural stones. As the name implies, these rocks have undergone a process of metamorphosis or transformation from their original composition to another. Their origin is due to the lowering of original rock formations to regions deep under the earth's surface, where they were exposed to high pressures and temperatures for millions of years. In this way, limestone was transformed into marble, sandstone into quartzite and granite into gneiss, Typical brands include Bianco Carrara (marble), Silver Cloud (gneiss) and Kashmir White (granulite).
Azul da Bahia (plutonic, foyaite) An extremely expensive natural stone (> 500 €/m2) which is something of a prima donna. The blue colour is produced by the mineral sodalite and can be irreversibly destroyed by exposure to vinegar or lemon-juice.
The diagram below summarizes the main parameters of natural stones and gives an overview of some of their key laying properties.
Natural stones Igneous
Properties
Plutonic
Sedimentary
Metamorphic
Volcanic
Limestones
Others
Marble
Others
Water absorption
Low
High
High
High
Medium
Medium
Adhesion risk
Yes
No
No
No
No
Yes
Discoloration risk
Possible
Possible
Possible
High
Possible
Possible
Efflorescence risk
No
No
High
Possible
Possible
No
Translucency risk
No
No
Possible
No
High
No
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2. Laying of natural stones There are two basic problems that need to be solved when laying natural stones. Firstly, it is necessary to establish permanent adhesion; this is especially important in the case of magmatic and metamorphic rocks (except for types of marble). Secondly, discoloration and efflorescence must be avoided. This is particularly critical when laying sedimentary stones. Good adhesion is normally ensured by using polymer-modified mortars. Efflorescence and discoloration can be prevented by ensuring a low water-cement ratio and rapid water absorption by the mortar. When laying highly absorbent natural stones, excessive water must not be used in the mortar. To ensure rapid curing, a laying temperature of at least +15°C is recommended. Especially for highly absorbent stones such as Jura marble or Padang granite, it is important to ensure that the stones are laid without any voids in the mortar bed; otherwise, lumps or lines of mortar under the stone may appear as dark spots on the surface. Over the past few years, flowable mortars have been used increasingly widely for floor coverings. These effectively prevent voids in the mortar bed to a sufficient extent for practical purposes. In the case of thin and medium-thickness mortar beds, this requirement can only be met by a combined buttering and floating process. In the case of translucent natural stones such as Bianco Carrara, special mortars based on white cement must also be used.
Blue Pearl (plutonic, syenite) This very popular natural stone, which has a bluish-grey sheen, is also marketed under the trade name of Labrador. When laying this stone, it is important to remember that the feldspar crystals will produce different reflections depending on the orientation of the slabs (dark and light effects). A harmonious appearance can be ensured by positioning the individual tiles in the appropriate direction.
Porphyry (volcanic, rhyolite) Porphyry often contains glass veins which function as separating layers and natural break points. This stone is extremely hard and very difficult to machine. A very sturdy stone that is mainly marketed as paving stones or flagstones.
Jura Grey (sedimentary, limestone) Limestones have formed over more than 100 million years by the precipitation of lime from the sea. There is a severe risk of discoloration and efflorescent as limestone often features inclusions of vegetable and animal matter as well as free lime. Limestones are highly sensitive to acid cleaning agents.
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3. Special cases 3.1 Engineered stone tiles
Bianco Carrara (metamorphic, marble) The king of marbles. An almost completely pure white natural stone with "quartzite" (really graphite) veins. These veins represent slip locations and possible break points. Small holes (taroli) are unavoidable.
Multicolor (metamorphic, migmatite) The name is appropriate. The structuring graphically demonstrates the severe forces involved in the transformation process. Each tile is unique, which makes it impossible to form a pattern.
Engineered stone tiles are made by embedding natural stone, sand and hard stone particles in a synthetic resin (polyester or epoxy) matrix. Typical natural stones used for this purpose include marble, granite and quartzite. However, in order to meet high aesthetic requirements, mother of pearl, mirror glass and semi-precious stones such as lapis lazuli may also be bound into the resin matrix, There is scarcely any limit to the creativity of the client or manufacturer. Engineered stone is produced in high-density slabs or blocks in a computer-controlled high-pressure process with simultaneous vibration and evacuation of air inclusions. Engineered stone tiles therefore normally have a tightly packed structure with low porosity. The water absorption properties depend on the natural stone material used. When laying engineered stone tiles, special attention must be paid to the mortar. The gauging water used may cause concave arching of the tiles and lead to saponification of the binding agent at the boundary between the tile and the mortar. For reliable laying, rapidly hardening mortar must be used. As the thermal expansion coefficient of engineered stone is some three times as high as for ceramic tiles, expansion joints are especially important. If the floor covering is exposed to temperature fluctuations, a rapidly hardening flow-bed mortar of a highly polymer-modified type must be used. Deformation properties depend on the natural stone material used as well as the size and thickness of the tile. Special attention must be paid to synthetic resin engineered stone with Verdi Alpi (serpentinite) inclusions. A water-free reactive resin adhesive must be used for laying tiles of this type. Because of their pronounced thermal expansion and sensitivity to moisture, artificial stone tiles are generally not suitable for outdoor use.
Kashmir White (metamorphic, granulite) This natural stone from India is not only decorative but also sturdy. However, the red granite inclusions may "rust" if exposed to water.
3.2 Slate Slate is a natural product with natural colour differences and a variety of surface structures. It was created about 400 million years ago from sediments of extremely fine clay sludge on the seabed, followed by the formation of mountain ranges at high pressures and temperatures. Mica slate, which has a silvery sheen, has an especially attractive appearance. The metallic effect is the result of fine particles of muscovite, positioned mainly in the cleavage surfaces. Depending on the amount of organic material in the original clay, oil slate sheets with soapy, water-repellent cleavage surfaces may be created. Depending on their origin, slate slabs may be subject to water absorption from the back, resulting in severe deformation. Oil slate tiles can only be laid reliably if the asphalt or oil is first removed from the back of the tiles using acetone and polymer-modified, rapid-curing mortars are used.
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3.3 Chinese granite (Padang) In the course of globalization, natural stones from China are finding their way to Europe, where they have become popular as a result of their low prices. Most of the Chinese stones are granites, which is marketed under the brand name of Padang G XYZ. "G" stands for granite and is followed by a three-digit number. The first figure (X) indicates the region and the second and third figures indicate the quality of the stone. In some cases, Chinese granites behave in a completely different way to their European "siblings". In comparison to European granite, they may simply soak up water although they have the same porosity values. Where a European granite may take up to 24 hours to become waterlogged, a Padang tile of the same thickness may reach the same state in a matter of minutes. If inappropriate mortars or laying techniques are used, Padang tiles may be affected by intensive, irreversible staining. This is especially the case if slow-setting mortar is used at low temperatures and/or there are voids in the mortar bed. To avoid staining of Padang floor coverings, the amount of free water must be reduced. Fast-curing mortars must be used and the temperature must be above 15°C. To ensure homogeneous colouring, the mortar bed must support the entire area of the tiles and be largely free from voids.
4. Grouting of natural stones Special attention must be paid to the grouting of natural stone tiles. If the correct grout is not used, components of the grout may penetrate the tiles from their edges, leading to the formation of a visible frame. Care must also be taken if the natural stone floor covering is to be ground and polished following laying and grouting, which is a relatively common practice in southern Europe. This is only possible if the grout used is free from quartz sand. The quartz sand in conventional grouts has an abrasive effect and would result in scratches on the surface of the stone. Elastic joint sealants must be free from plasticizers. Special smoothing agents must be used; otherwise, the appearance of the floor covering could be damaged in the last stage of the process. Normal detergents must not be used as they contain surface-active agents, dyestuffs, aromas and fatty substances which could result in ugly discoloration of the natural stones.
Our Advice! No. 19
5. Summary For the proper laying of natural stone and engineered stone tiles, mortar and grout with special cements, a low water-cement ratio and appropriate water-retaining properties must be used. As a general principle, excess water in the mortar must be avoided and laying temperatures from 15 to 25°C are recommended. This reduces the exposure of the tiles to free alkaline and water, which may have a detrimental effect. As a result, deformation, voids, discoloration, staining and efflorescence are avoided. Before starting with the laying work, tilers must consider the points listed in the table below: Parameter
Potential problem
Stones at risk
Porosity
Poor adhesion if porosity is too low Loss of adhesion during mortar curing phase as a result of concave arching Visibility of mortar bars or lumps
Plutonic and engineered stones Engineered stones, serpentinite, thin slate tiles Thin light-coloured tiles such as Carrara marble
Coloured impurities in the water used for the water appear on the stone surface Free lime is transferred to the surface of the stone by the mortar water Voids caused by waterrepellent oils, concave arching
Sedimentary stones, natural stones containing iron
Deformation
Translucency
Discoloration
Efflorescence
Slate
Engineered stones
Padang granite
Concave arching, saponification of the binding agent Irreversible surface marking by rapid water absorption
Limestone, marble
Solution • Rapid-curing polymer-modified mortar • Rapid-curing mortar • Laying temperature 15 to 25 °C • Reaction resin adhesive • White mortar • Scratch coating on back of tile • Laying without voids • Rapid-curing mortar
• Rapid-curing mortar • Laying temperature at least 10 °C
• Clean with acetone before laying if necessary • Rapid-curing highly polymermodified mortar Agglo marble, Agglo • Very rapid-curing polymer-modified slabs, engineered stone mortar • Reaction resin adhesive e.g. Padang G633, thin • Very rapid-curing mortar slabs • Laying temperature 15 to 25 °C • No excess water in mortar Oil slate, asphalt slate
Our Advice! No. 19
6. PCI standard recommendations The following table indicates the standard recommendations of PCI Augsburg for laying some widely used natural and engineered stone tiles.
Stone type
Thin bed
PCI mortar medium thickness
Thick bed
PCI grout cement-based)4 elastic
Plutonic rocks (granite, gabbro)
PCI Carraflex PCI Carraflott NT PCI Carralight
PCI Carrament grey/white
PCI Carraflott NT as bonding slurry
PCI Carrafug)4 PCI Flexfug)5 PCI Rapidfug
PCI Carraferm
Volcanic rocks (basalt, porphyry)
PCI Carraflex PCI Carraflott NT PCI Carralight
PCI Carrament grey/white
PCI Carraflott NT as bonding slurry
PCI Carrafug)4 PCI Flexfug)5 PCI Rapidfug
PCI Carraferm
-
PCI Carrafug)4 PCI Flexfug)5 PCI Rapidfug
PCI Carraferm
Padang granite)1
PCI Flexmörtel Schnell PCI Carrament grey PCI Carraflott NT
Limestones)2 (Jura marble, Solnhofen tiles)
PCI Carraflex PCI Carraflott NT PCI Carralight
PCI Carrament grey/white
PCI Carraflott NT as bonding slurry
PCI Carrafug)4 PCI Flexfug)5 PCI Rapidfug
PCI Carraferm
Other sedimentary rocks (sandstones)
PCI Carraflex PCI Carraflott NT PCI Carralight
PCI Carrament grey/white
PCI Carraflott NT as bonding slurry
PCI Carrafug)4 PCI Flexfug)5 PCI Rapidfug
PCI Carraferm
Marble)2 (Blanca Carrara)
PCI Carraflex PCI Carraflott NT PCI Carralight
PCI Carrament white
PCI Carraflott NT as bonding slurry
Slate)1 (oil and mica slate)
PCI Carraflex PCI Flexmörtel Schnell PCI Carrament grey PCI Durapox NT)3 )3 PCI Collastic
PCI Carrafug)4
PCI Carraferm
-
PCI Carrafug)4 PCI Flexfug)5 PCI Rapidfug
PCI Carraferm
PCI Carrament grey/white
PCI Carraflott NT as bonding slurry
PCI Carrafug)4 PCI Flexfug)5 PCI Rapidfug
PCI Carraferm
PCI Carrafug)4 PCI Flexfug)5 PCI Rapidfug
PCI Carraferm
PCI Carrafug)4 PCI Flexfug)5 PCI Rapidfug
PCI Carraferm
Other metamorphic rocks (gneiss, granulite)
PCI Carraflex PCI Carraflott NT PCI Carralight
Translucent stones (marble, limestone)
PCI Carraflex PCI Carraflott NT PCI Carralight
PCI Carrament white
PCI Carraflott NT as bonding slurry
Engineered stones)1 (Agglo marble)
PCI Flexmörtel Schnell PCI Carraflott NT PCI Durapox NT)3
PCI Carrament grey/white
PCI Novoment M1/Z1 in combination with PCI Carraflott NT as bonding slurry
)1
Laying temperature 15 to 25°C; no excess water in mortar See also translucent stones For strongly deforming natural and engineered stones, e.g. with Verdi Alpi inclusions )4 Not suitable for grinding )5 Only for polished natural stones )2 )3
Anhydrite floated screeds, cement-based screeds, gypsum plaster and concrete substrates must be primed with PCI Gisogrund or PCI Gisogrund Rapid prior to laying. Prior to laying on old ceramic or natural stone surfaces, the substrate should be prepared using PCI Gisogrund 303. More detailed information on special substrates and natural stones is given in our natural stone brochure (No. 2152). For further advice, please contact the PCI Technical Service department.
Our Advice! No. 19
PCI Augsburg GmbH Piccardstr. 11 86159 Augsburg P.O.B. 10 22 47 86012 Augsburg Germany Phone 0049 (0) 821/59 01-0 Fax 0049 (0) 821/59 01-390 www.pci-augsburg.de
The specifications in this issue of “Our Advice!” meet the latest state of technical knowledge. Subject to technical alterations. Edition: June 2010
