Preparing the floor surface for tiles
Surfaces to be tiled should be dry, flat, stable, clean and free from grease, dirt and unsound material. A flat, dry, level concrete floor can be tiled without special preparation. If, however, there are small depressions in the concrete these should be filled with a mortar mix of 3 parts sharp sand and 1 part cement.
A more uneven floor should be screeded with a proprietary brand of self-levelling flooring compound. The screed should be left for two weeks to allow it to dry thoroughly before fixing tiles. If the floor is a new concrete one, it should be left for a minimum of four weeks to allow all moisture. to disperse before you begin covering it with tiles.
Existing ceramic floor tiles, quarry tiles or terrazzo surfaces can be tiled over. They should be checked to ensure that there are no loose or hollow-sounding areas. Any defective sections must be made good before you lay new tiles on top. You can tile on suspended wooden floors, but it is important that the floor should be made as rigid and firm as possible.
To achieve this, cover the floorboards with a layer of water-resistant resin-bonded plywood at least 12mm (1/2in) thick. Alternatively, you can use chipboard of the same thickness. Before laying tiles over timber floors cover the surface thoroughly with a priming coat – either a special priming agent from the adhesive manufacturer, or else diluted PVA building adhesive.