What Grade of Plywood Is for Subfloor Tiles?

Interior Grade

• Interior plywood can be used in situations where you know you are including some form of cement-board underlayment or mud base on top of the wood for the tile installation. You still need to install the recommended size of plywood, depending on ceramic tile or natural stone installation, but interior plywood is an acceptable subfloor material.

Exterior Grade

• If you plan on installing the tile directly on top of the plywood, or you are installing a plywood subfloor in a wet area such as a bathroom or under the kitchen area, you need to use exterior grade plywood. This type of plywood is treated to stand up to water better than interior-grade plywood.

Specialty Thinset

• Thinsets that are rated for use with plywood must be taken into consideration. Installing tile directly onto the subfloor is not the preferred installation method, as concrete or fiber board underlayments are recommended. Still, there are specialty thinsets available which allow you to install the tile directly on top of the plywood, so long as it is high-quality, exterior-grade plywood.

Layers

• Ceramic tile installations require at least two sheets of five-eighths-inch material stacked on top of each other to provide support as a subfloor. Natural stone installations require two sheets that are three-quarters of an inch thick. Underlayment does not count as a subfloor material.