Sealing your shower walls is essential for tiling the surface to prevent moisture from effecting the integrity of your tile installation. Plywood or drywall is insufficient as a subfloor because it is a permeable material that will rot away when exposed to water. Cement backer board, a type of wall board made of fiberglass and portland cement, needs to be installed over the plywood or drywall. Cement back board is available at most home improvement and tile supply stores in both 3/8-inch and 5/8-inch thicknesses. Both are effective at protecting against moisture; the difference in thickness depends on how much additional thickness your wall can allow.
Things You'll Need
Cement backer board
1/2-inch notched trowel
Galvanized cement screws
Fiberglas mesh tape
Measure the area that the cement board will occupy in the shower and any points at which accessories will protrude through the tile. Transfer these measurements to the cement backer board and cut them with the jigsaw to accommodate the space.
Mix the thinset according to the manufacturer's instructions. Spread the thinset with the notched trowel over the area that one of the backer boards will occupy. Firmly press the cement backer board against the thinset.
Screw the galvanized screws into the cement backer board every six inches along the edge and every 16 inches elsewhere. Screw the heads in far enough that they do not stick out at all.
Repeat to complete the rest of the shower. Run the Fiberglas mesh tape along where two pieces of board meet.
Install tile over cement backer board.
Cement Backer Board has very rough edges. It is recommended that you wear durable leather gloves when handling.