By Jim Percival, technical director, Palace Chemicals, considers how the benefits of underfloor heating (UFH) can be safely enjoyed in combination with large format tiling installations
Large format tiles are increasingly popular in both residential and commercial projects, offering a clean, contemporary finish with fewer grout joints. When combined with UFH, whether a wet system or electric, large format tiles can provide an excellent way of transferring heat efficiently into a room. However, the combination requires careful planning, preparation and installation if the finished floor is to remain trouble-free.
One of the key considerations when tiling over UFH is movement. As the heating system operates, the substrate and tile installation will undergo repeated cycles of heating and cooling. These movements need to be accommodated within the flooring system, and not transferred to the tiles or grout joints.
Good substrate preparation and the incorporation of movement joints around all perimeters, in line with substrate joints and at defined intervals in large floor spaces are therefore important considerations. The screed or other substrate must be suitable for the particular UFH system and must have reached its required level of dryness for its material type before tiling begins. With heated screeds, the system should be commissioned and the heating cycle completed at a step-wise rate of temperature increase in accordance with the screed and heating manufacturers’ recommendations. Rushing this stage can increase the risk of cracking, tenting, debonding or other failures.
The above is true for all tiling jobs involving UFH. The use of large format tiles means that the preparation stages are even more important. The size of the tiles means they are less tolerant of variations or movement in the substrate, and achieving adequate adhesive coverage is critical. The reduction in the number of grout lines, which is a key aesthetic benefit of large format tiles, also means there is less flexibility to absorb movement.
The substrate should therefore be sufficiently flat and the adhesive generously applied to prevent voids beneath the tile. It also means a flexible cementitious adhesive should be selected which is approporiate for both the tile and the substrate. The adhesive should be applied using a back-buttering technique to achieve 100% coverage between the tile back and the substrate.
When correctly designed, prepared and installed, large format tiles and UFH make an excellent combination. The most important thing is to treat the complete floor as a system, rather than considering the tiles, adhesive, substrate and heating independently.
