Backerboard is a moisture and mold resistant material used when installing tile in wet areas such as the bathroom and kitchen. Using backerboard will insure protection against moisture damage and mold growth. This is a special step before installation that can greatly improve the durability and longevity of any tiled wall in wet or humid areas.
Backerboard must be installed with its edges centered on joists, so you will need to mark the location of each joist before spreading the mortar. Mark the locations of the joists on the wall using a stud finder as a guide. Leave at least 1/8-inch between sheets and 1/4-inch gap at the walls when laying the backerboard. Measure and cut backerboard as needed.
Mix thinset and pour out on the floor. Hold the smooth side of the notched trowel at a 30 degree angle and spread the mortar in a thick, even coat over enough area for a piece of backerboard. Use the notched edge at an angle and work the mortar into ridges.
While the mortar is still wet, tip the backerboard on a long edge and hinge it toward the floor. Line the first board along a joist for stability. Follow manufacturers directions but typically you should stagger the joins. Walk on the board to set it into the mortar.
Drive backerboard screws through the board into the sub-floor spacing every 8". Use 2" screws at the joists and 1 1/4" through the rest of the board.
Use 2" pregummed fiberglass mesh tape over each joint. Press the tape firmly onto the backerboard. Finish the joint by applying a thin coat of mortar over the tape. Feather the edges to avoid high spots. The backerboard is now ready for tile.