Plywood Underlayment


Select or Select-Tight Face grades of 7.5 mm (5/16") or 9.5 mm (3/8")plywood, or special underlayment panels made by several CANPLY members, are recommended for use as underlayment under resilient floor finishes such as vinyl, rubber and synthetic sheets or tiles, ceramic tiles and those types of glued-on carpets for which the manufacturer recommends the use of underlayment.

Underlayment is also used to compensate for the difference in thickness between thinner resilient flooring and thicker flooring such as hardwood or carpet.








Underlayment panels should not be installed until wood subfloors, concrete, plaster and lumber framing have dried to the approximate conditions that will exist in the structure during occupancy. Also, underlayment panels should be allowed to acclimatize in room conditions. To achieve this, it is recommended that the panels be placed separately on edge around the room for a minimum of 48 hours prior to installation of the finished floor.

Underlayment panels should be laid at right angles to subflooring panels with joints in underlayment staggered and offset at least 200 mm from joints in subflooring, and with ends and edges butted to light contact.

Unless specified otherwise by the manufacturer, underlayment panels shall be nailed or stapled every 100 mm along edges (10 mm to 15 mm from edge), and every 150 mm throughout the rest of the panel. Use 25 mm ring grooved underlay flooring nails, or 28 mm long staples with 5 mm crowns and not less than 1.2 mm shank diameter. Avoid nailing underlayment to joists supporting the subfloor. Nailing or stapling should begin at one corner of the underlayment panel and should progress diagonally across the panel.

For ceramic tiles applied with adhesive, 11 mm thick underlayment is required where supports are spaced wider than 300 mm on centre.

Preparation of underlayment prior to applying floor covering should be done as recommended by the floor covering manufacturer. Such a recommendation should include sanding uneven surfaces and panel joints to level, filling surface voids according to the floor covering manufacturer's procedure and, when required by the manufacturer, a procedure for filling joint seams. It should also include specification for a suitable filler.

Plywood Underlayment Installation