Plating with natural stone
System solutions for placing the stone products
In addition to the suitable natural stone, the plating also requires a smart choice of the system for stone plating. The way of plating, together with the other things, depends on the place of plating, type of natural stone, its technical and physical characteristics, binders and available height for stone installing.
Classic usage of cement mortar is less used because of its insufficient consistence and uneven solidification. The oldest way of natural stone plating is placing it directly on the cement mortar. The layer of wet mixed sand which is 3-5cm thick and cement is covered with cement milk and in the end the stone panels are placed.
Although ten years ago this system was mostly used for placing the stones in exterior spaces, today it is not recommended any more. Since the stone panels do not enable the sealing of the exterior surfaces, after a longer period water penetrates to mortar and the water which freezes during winter causes the damage of the estrich layer beneath the mortar. On the contacts of stone panels often some cracking appears and nitro from the cement mortar is extracted on lower surfaces. Besides that, the system does not enable a solid enough connection of cement milk and stone panels which absorb less, such as shale or artificial stone.
Covering with the adhesives enables a necessary connection with the foundation
Nowadays, the natural stone in interior and exterior spaces is usually placed on adhesives based on special hydraulic binders or adhesives based on reaction base. In bathrooms, balconies and exterior surfaces on which the humidity could reach beneath the natural stone panel, on the surface made of estrich is placed a hydroinsulation coat based on cement. The adhesive is chosen depending on:
- the place of stone installing (interior or exterior)
- the foundation on which the stone is glued (e.g. cement estrich, metal, etc.)
- surface load
- the type of natural stone.
The cement based adhesives of C1 class are suitable only for stone placing in interiors with low surface load. Taking into consideration that the estrich surface is often not flat, before stone placing the surface should be levelled using the self-levelling compound or a thick level of adhesive. When it comes to placing light freestone, the stone on the surface can be coloured and therefore white, fast-binding adhesives should be used. If the stone panels are reinforced at the back with a net and polyurethane coating, before the placing on the cement adhesive they should be coated on their back or to place the stone onto the polyurethane adhesive which is used for stone placing on metal and wooden surface.
Placing on the drain concrete stops keeping water on the surface
The system of placing on the drain concrete is used when the stone is placed on the exterior surfaces which do not have a basement under them. On the drain supporting layer of concrete or asphalt the stone is placed onto the one-grain concrete made of crushed stone or of round grains. The system is the most suitable for exteriors for many reasons:
- it transfers the forces in the most optimal way because the grains in the concrete rest on each other,
- it takes away the water which does not stay in the concrete,
- it enables the resistance to salt against freezing because the water does not stay.
The pointing is done by the cement mortar filling the entire depth of the holes. If during the winter, the surface is strewed by antifreezing salt, the mortar has to be resistant to salt in order not to adulterate the quality of the mortar on the surface. Because if the temperature changes and concrete shrinkage, the panels placed on the drain concrete usually crack on the cement mass for pointing. (Lannica, 2002).
The system of the elevated flooring is suitable for low level of load surface floors (e.g. terraces of the apartment buildings or office buildings) when you wish to bridge the height difference between the slanting estrich and the stone surface. On the concrete panel, the hydroinsulation should be done together with the protection using a slanting estrich. Cement based hydroinsulation layer should be placed on it, e.g. Mapelastic. Using the dowels you can regulate the final height of the stone floor. Through the open apertures between the panels water flows to the slanting estrich and goes to the system for drainage of meteoric water. The stone panels can be reinforced if need be to achieve a satisfying resistance to bending.
Appropriate dilatation of stone flooring
When planning a good stone flooring attention should be paid to planning and execution of dilatation pointing which prevents the later deviation or panel cracking because of shrinkage, hardening or bending. On all the places which are prone to experience stress in the estrich to which the panels are placed on, elastic pointing should be done. Next to the construction joints and the joints of stone panels along the walls and the columns, it is necessary to do estrich dilatation is the surface is bigger than 25m2.
For making dilatation pointing, today people mostly use elastic one-component sealing compounds based on polyurethane which harden in the moist.
To achieve an optimal elasticity, a balanced proportion between the width and the depth of the pointing joints is necessary, and it has to adhere only to the sides of the pointing joints. Therefore before the pointing is done, the bottom should be filled with a foundation made of foamy polyethylene. Mistakes with pointing do not allow the spreading of the foundation.
|distance between the joints in m||width of the joint in mm||depth of the joint in mm|
|to 2 m||15||10||8||± 2|
|from 2 to 3.5 m||20||15||10||± 2|
|from 3.5 to 5m||25||20||12||± 2|
|from 5 to 6 m||30||25||15||± 2|
|from 6 to 8 m||35||30||15||± 2|
|1. Basic dimension for planning
2. Minimal dimension in the time of making joints using caulking mass
3. The values in the table are for final dimensions of the joints
Table 1. Dimensioning of dilatation joints. Source: Otto-Chemie, 2004.
Dilatation joints must be properly dimensioned (table 1). The width of the dilatation joint depends on the characteristics of the caulking mass, susceptibility of the construction elements, coefficient of width of the natural stone which is being placed and the distance between the two dilatation layers. The width of the joints should be between 10 and 30 mm.
Dilatation mass takes over 25% of the joint purpose and if the width of the joints is too small or a pre-lubricant for better joining of stones is not used, usually cracks appear between the stone and the caulking mass or the caulking mass is tearing apart.
Along with dimensioning of the dilatation joints, the time of their making and caulking is also important. When the air temperature is high, the expansion of the stone is the highest and because of that the caulking mass cannot handle the shrinkage in the colder days. Dilatation joint must be placed right above the dilatation on the foundation made of estrich. The smallest discrepancy can later bring to the stone breaking on the same place where the dilatation on the estrich is.