Walls

• Cement board manufacturers note that 1/2-inch (or thicker) cement board is required for installing large tiles on wall applications. The exception to this rule is wall surfaces covered with plywood sheathing. In this case manufacturers say that 1/4-inch cement board is appropriate. Nevertheless, because of its additional mass, large wall tile is often best installed with 1/2-to-5/8-inch cement board.
  
  

Flooring

• Manufacturers note that 1/4- and 1/2-inch cement boards are appropriate for tile flooring. Large tile flooring is not an exception to this rule. Subfloors should be 5/8-inch plywood sheathed, and areas that exceed 36 feet in length should incorporate tile expansion joints.
  
  

Additional Considerations

• Installing thick cement board is more labor intensive than 1/4-inch board, but the extra work may be worth the effort. For example, large floor tiles installed on 1/4-inch cement board may not be as soundproof as large floor tile installed on 1/2-inch cement board.