The materials needed to waterproof a bathroom wall include a vapor barrier, cement backerboard, thinset mortar and a waterproof membrane. These materials help prevent water from saturating wood and to prevent mold growth, which can lead to expensive repairs in the future.
Vapor barriers protect the wood behind bathroom walls from moisture buildup. Over time, moisture from hot, running water can seep in between cracks in tile and stone and onto wood surfaces. Without a vapor barrier, the wood becomes brittle and weak, which can cause walls to buckle and tile to crack.
Cement backerboards cover vapor barriers to provide additional protection from moisture and water damage. Thinset mortar and a waterproof membrane, when applied to cement backerboard, help seal backerboard joints and any construction holes. A waterproof membrane also creates a smooth surface for the tile or stone installation.
In addition to cement backerboard, thinset mortar and a waterproof membrane, a single plastic, tile-like sheet specifically made to prevent water damage may also help protect bathroom walls from water and moisture damage. Other materials used to waterproof a bathroom wall include seam tape to cover cement backerboard joints, water sealant and caulk to seal bathtub and shower stall edges to prevent water from settling behind the walls.