Preparing Floors for Tiling

Wooden Floors

Tiles must be laid on a level, firm base because any flexing will crack the grouting. It's essential that there is a flow of air under the floor to stop condensation forming. Check that the airbricks around the external walls aren't blocked with debris or earth. If they are, clear them and check under the floor for signs of damp or mould - such problems will need professional treatment before the tiles can be laid.

Replace damaged or rotten boards and cover the floor with sheets of 12 mm (1/2 in) exterior-grade plywood, fixed with rustproof screws at 300 mm (12 in) intervals. Pay special attention to the edges and joints. Next, brush on two coats of a PVA-based sealer to stop the plywood absorbing the floor adhesive.

Remove skirting boards and door thresholds so you can tile under these. You will probably need to trim some timber off the bottom of the door as well.

Concrete Floors

These are ideal for tiling as long as there is no damp. New floors have a damp-proof membrane fitted, but if you suspect damp, the floor may need to be coated with a waterproofing compound. Call in a professional for advice.

Otherwise, fill any large holes or cracks with self-levelling compound - a powder that is mixed with water and poured over the cracks and hollows - to form a smooth, flat base for the new tiles. Brush a coat of concrete floor sealer over the whole floor.

Remove skirting boards and door thresholds before starting work.