Membranes

Install a membrane wherever a floor exhibits the potential of cracking tile or allowing water to penetrate. Isolation and waterproofing membranes are appropriate for hard-bodied tiles and are also necessary for certain vinyl and laminate installations.

Isolation membranes
These materials allow substrates to expand and contract without telegraphing the movement to the tile. Two-part membranes, adhesive and mesh or chlorinated polyethylene (CPE), are applied directly to the surface to be tiled. The easiest materials to use employ a roller-applied adhesive. On old stable concrete, cover each crack separately. On new concrete that you suspect will crack with age, cover the entire floor.

Waterproofing membranes
Use a waterproofing membrane in shower enclosures and any area that will get wet. Felt paper, polyurethane sheets, and two-part products work well. Many products function as both a waterproofing and isolation membrane.