How Thick Should Cement Board Walls Be?

Matching Heights

• The most common way to install cement boards for tile installations is to hang the cement board on the wall in the same fashion as you hang drywall. The drywall is usually cut off at the exterior perimeter of the shower or wet area and the exposed studs are left to be covered by cement board instead. A matching thickness of cement board is used to create the same finish thickness.

Raw Studs

• Raw stud installations, where there is nothing but the studs existing, require you to use a minimum of half-inch thick concrete board. It is easily found in any home improvement store and matches the thickness of standard drywall. Because of the spacing between the studs, you need to use at least half-inch thick material so there is no deflection, which is movement, between the studs due to too-thin material.

Existing Plywood

• For walls that have existing plywood in place, the deflection issue is taken out of the equation, but because wood is not an acceptable underlayment for tile, you still need to include a layer of concrete board. In this case, you can use the quarter-inch thick material sold at your local home improvement store, as you only need a layer for the thinset mortar to bond with.

Doubling Up

• If you come across a situation where there is three-quarter inch drywall in use, or some other thicker variation, most people want to flush out the concrete board with the drywall face. However, you cannot simply install concrete boards on top of each other. Instead, you should add a layer of plywood first and then install an appropriately thick layer of concrete board on top of that.