Floor and Wall Tiles Works:
Start by removing the existing flooring. Scrape off any residual adhesives or mortar, and clean the floor thoroughly.
Check to see that the subfloor is flat and level. Fill any low spots and cracks in a concrete subfloor with concrete patching compound.
For wood framing, make sure the subfloor is dry, rigid, and securely attached to the joists.
Never apply tile directly to plywood or a wood subfloor. Instead, cover the subfloor with cement backer board, using corrosion resistant screws that are countersunk flush with the surface of the backer board.