The Proper Thickness of a Subfloor for Ceramic Tile

Minimum Recommendations

• Ceramic tile installations require stability so the tiles stay adhered to the thinset mortar and the grout stays in the joints. The minimum allotment for subfloors is two sheets of 5/8-inch plywood or some other type of approved subfloor for ceramic tile. The minimum thickness should be 1 and 1/4-inch thick, although you can go thicker if you have large-bodied tiles and want to be on the safe side.

Board or Plank Floors

• Existing board or plank floors, such as hardwood floors, need another layer of solid wood installed on top of them. Plank flooring is not an acceptable substrate for ceramic tile installations, and they need another layer added to the subfloor for proper installation. You need to use at least 3/4-inch thick plywood to cover plank floors.

Minimum Spacing

• Depending on the type of thinset you are planning to use on the installation you may need to add additional spacing to the subfloor, adding to the overall thickness. For latex-thinset installations, you need 1/8 inch of space between the two sheets of plywood, while epoxy thinset installations require 1/4 inch of space between the sheets. This is to accommodate the natural swelling of the materials in the warmer months.

Mud Jobs

• For a tried and true underlayment that will last for years, you can install a mud base for your ceramic tile installation. This is a layer of cement, sand and lime that is at least 3/4 inch thick and is the basis for the concrete boards that are now sold in home improvement stores. For these installations, you only need a 3/4-inch thick subfloor beneath the mud, as the mud also provides a minimum thickness.