- Q.We will be installing ceramic tile flooring in
the kitchen of an existing house. The subfloor consists of
1/2-inch plywood over 3/4-inch particleboard (not OSB). The
joists are spaced 16-inches on-center. My plan is to install
1/2-inch cementitious backerboard on the plywood and then
install the tile. Will this be adequate?
A.Chip O’Rear, assistant executive director
of the National Tile Contractors Association, responds:
Particleboard, which easily absorbs moisture and is
dimensionally unstable, shouldn’t be included anywhere as
part of a tile substrate. In this case, the existing plywood
and particleboard subfloor layers will have to be removed and a
new subfloor installed on the joists.
The best subfloor for a backerboard and tile installation is
3/4-inch plywood, glued with subfloor adhesive and mechanically
fastened every 8 to 12 inches in the field, and every 6 inches
on the edges. Leave a 1/8-inch gap between plywood sheets for
expansion relief. Then install your 1/2-inch backerboard in a
freshly combed bed of thinset (to give uniform support),
fastening the backerboard with corrosion-resistant fasteners.
Since installation requirements vary depending on the
backerboard manufacturer, always verify a manufacturer’s
requirements before proceeding.