Floor tiling with very large tiles
Recently, the use of larger tiles has become common practice. This has placed extra burden of the adhesive used, which needs to be highly flexible and allow for easy bedding.
Substrates move slightly with changes in temperature and moisture and structural movement
When a substrate expands or contracts even slightly, due to changes in temperature or water content, the tile being of a different material will change by a different amount. This can arise for a number of reasons, for example:
- Shrinkage in a screed as it dries
- Thermal expansion in hot weather
- Moisture-induced expansion on getting waterlogged
- Thermal cycling of under-floor/ under-tile warming systems
Larger tiles suffer higher strain levels than smaller tiles
The increase in strain is cumulative across the width of the tile i.e. the further a contact point is from the centre of a tile, the more adjacent points in the tile and the substrate will be stretched away from each other.
So for a given set of circumstances, a smaller tile will be less likely to delaminate than a larger one.
Large tiles are placed under more stress by any deflection in the floor
When a non-rigid substrate deflects, the rigid tile cannot withstand the deflection.
For a given deflection in the substrate, the chord height that the tile tries to bridge will be higher for larger tiles.
This results in higher stresses and therefore requires greater flexibility in the tile adhesive to prevent failure when fixing larger tiles.
It is necessary to select an adhesive with the appropriate level of flexibility to accommodate the expected strains from either differential thermal or moisture movement and/or deflection of the substrate under load. There are many possible permutations, so we have indicated some guidelines below.
Rigid substrates : (e.g. sand/cement screeds, concrete)
- Ceramic tiles up to and including 420 x 420 mm: weber.set Ceramic S
- Ceramic tiles greater than 420 x 420 mm: weber.set Ceramic L
- Porcelain tiles up to and including 600 x 600 mm: weber.set Porcelain S
- Porcelain tiles greater than 600 x 600 mm: weber.set Porcelain L
Substrates with limited movement (e.g. over-boarded wooden floors, screeds with under-floor heating)
- Tiles up to 1600 cm2 (400 x 400 mm): weber.set Ultra-flex
With larger tiles, the force needed to bed them correctly increases dramatically. If 2 kg of force is needed to bed a 10 x 10 cm tile, 32 kg is needed to bed a 40 x 40 cm tile. It is therefore very important that the correct trowel, method and adhesive are used. Specially developed adhesives such as the weber.set Ultra-flex, help achieve a solid bed, even on large tiles.
Relative flexibility of adhesives (based on transverse deformation)
The graphic indicates the relative flexibility of the various alternaive rapid setting adhesives in the range. It provides guidance to suitable substitutuions and the heirarchy of performance
Solution with the following weber products
A cement-based tile adhesive for small format Ceramic tiles (smaller than or equal to 420 x 420 mm)
A cement-based tile adhesive for large format Ceramic tiles (larger than 420 x 420 mm)
A cement-based tile adhesive for all small format Porcelain tiles (less than or equal to 600 x 600 mm)
A high strength, cement-based tile adhesive for all large format Porcelain tiles (larger than 600 x 600 mm)
A highly deformable, fast setting, high strength cement-based tile adhesive for all types of tiles.