First, remove any cupboards that you intend to tile behind. Remove any unwanted screws, hooks, brackets, old pipes or other ‘rubbish’ and, if you have unsightly wiring on the wall surface, cut it back into the wall. If the skirting boards are battered, you may also decide to restore or replace them. Against a bright new surface, any unsightly old items will ‘scream’. The area should be dry, clean, flat and firm. Fill out any cracks and irregularities with cellulose filler or plaster, and rub down to a flat surface when dry. Newly plastered surfaces should be completely dry and, if dusty, brushed down with a wire brush to remove any loose material, If the surface is porous, a sealant primer should be used to prevent absorption of the adhesive into the plaster. If the surface has been previously painted and the paint is sound, you can tile straight on to it (score gloss paint to help adhesion). Otherwise, strip the paint with a sanding block and medium glasspaper. It is possible to tile over old tiles if they are sound and the surface is firm and flat.
But well worth considering chipping off the old tiles and their backing mortar, making good the surface and starting afresh. A club hammer and a bolster will make short work of the old tiles, or an electric rotary hammer can be hired to remove a large area. Building boards, such as plywood, chipboard and plasterboard, provide good tiling surfaces, but nust be removed, stiffened and replaced to prevent them from sagging and warping. Appropriate battening of 75mm x 50mm timber at about 304mm centres, horizontally and vertically, will give the necessary rigidity. If the board has a rough side, use this as the surface for the tiles. Use a heavy duty adhesive, and seal the untiled side-an ordinary paint undercoat can be used-to prevent moisture from the adhesive from seeping through. For floor tiles, the surface must be dry and well brushed, and sealed with an anti-dusting agent. Newly laid concrete surfaces must be completely dry-allow a month for each inch of depth. If the floor is solid and uneven, clean it and relevel it. If necessary, remove the surface and re-screed the floor, or use a proprietary self-levelling compound. Timber floors also need to be levelled.