Can Ceramic Tiles Be Laid on Top of a Hardwood Floor Without Underlayment?

Exterior Plywood

• The only acceptable type of wood that tile can be installed on top of is exterior plywood, but even in this case you must use a specialty thinset mortar that is designed to be used with wood. However, this thinset only works with exterior-grade plywood and is not rated for use with hardwood floors. Exterior plywood is specially designed with resins to provide the strength necessary for a tile floor.

Underlayment

• The main purpose of underlayments is to provide tile installations with a cementitious layer of something for the mortar to adhere to. They are not structurally supportive, nor do they add anything to the structural strength of a subfloor. As a result, they are not a substitute for subfloors themselves. All tile installations require a subfloor beneath them for stability, and underlayment alone is not it.

Hardwood Floors

• Regardless of whether hardwood floors are nailed down or installed in floating format, they provide far too much movement to be a base for tile installations. Not only is there vertical swell between each individual piece and the piece next to it, there is also horizontal swell. Wood expands in the summer months, buckling upward and expanding outward, and once the pieces are installed, they are still individual pieces of wood slatted together. Tile installations on top of hardwood will pop off the floor within months, if not weeks, due to the movement.

New Subfloor

• The proper way to install tile on top of a hardwood floor is to add an appropriately thick layer of subfloor on top of the hardwood floor. For ceramic tile installations, this is two sheets of five-eighths-inch-thick plywood, stacked on top of each other, or two sheets of three-quarter-inch material for natural stone tile installations. Underlayment or exterior plywood should then be installed on top.