A prerequisite for the installation of large format tiles is a flat substrate. The larger the tiles, the flatter the substrate needs to be.
A substrate, which conforms to the requirements of DIN 18 202 for producing surfaces, is not always adequate for the installation of large format tiles. Levelling of uneven areas and irregularities during tile installation is almost impossible with large format tiles. Render and screeds must therefore be largely flat. If this is not the case then a levelling coat will be needed. Various levelling materials are suitable such as SOLOPLAN-30-PLUS, ASO-NM15 (self-levelling) or SOLOCRET-15 (non sag).
Above a format of 40/40 cm, apply a contact layer to the rear of the tiles. If this contact coat is not adequate to fully cover the rear of the tile, then use the floating buttering method. When an adequate bond between the material installed and the substrate is achieved, then any stresses, which occur can be reliably dispelled and cracks in the finsh prevented.
Any residual moisture present beneath the tiling e.g. from the concrete slab, screed and adhesive, can only very slowly dry out through the small number of joints. Where substrates are sensitive to moisture, this can lead to damage. The appropriate primer should be used to afford adequate protection.
1) With cement-based thin-bed adhesives we recommend the addition of polymer dispersions such as UNIFLEX-B to compensate for stresses between substrate and ceramic tile.