Concrete resurfacing over wood or plywood substrates

During renovation and remodeling of existing buildings, more and more people are looking for ways to convert their existing wood or plywood subfloors into concrete floors. The daily temperature and humidity changes cause the wood floors to move and expand under stress. The joints between boards and rough uneven surfaces become pronounced. Traditional latex-modified or gypsum based underlayments will crack along joints, break bond with lateral wood movement, and often strong enough to withstand the traffic.

Plywood Substrate in a kitchen

Plywood Substrate in a kitchen

Metal lath stapled over plywood substrate

Metal lath stapled over plywood substrate

The installation of calcium aluminate cement based self-leveling concrete, Param 5500 along with expanded metal lath for reinforcement is a successful fast-track method to convert a plywood subfloor into a beautiful concrete floor. We recommend applying Param 5500 at a minimum thickness of 3/8” (1/2" is preferred) to withstand lateral movement and traffic stress.

Self leveling concrete covering metal lath

Self leveling concrete covering metal lath

Steps:

  1. The wood subfloor must either be solid hardwood flooring, a minimum of ¾” tongue-and-groove, APA – rated, Type 1, exterior exposure plywood, or OSB equivalent. The subfloor should be solid and fixed securely to provide a rigid base. Any boards exhibiting movement should be renailed. The surface of the wood must be clean and free of oil, grease, wax, dirt, varnish, shellac, or any contaminant that might act as a bond breaker. We recommend sanding the wood surface with 60 grit sanding screen under floor maintainer.
  2. The open joints should be filled with a rapid-setting patching compound.
  3. After the wood surface is thoroughly prepared, prime the surface with Param Primer. The primer solution should be distributed evenly over the floor surface and then brushed into the substrate with a soft bristled push broom. Avoid pudding of primer. When applying with a pump sprayer, make sure to cover the substrate with an even coat to ensure proper penetration and follow immediately behind to work into the surface with a push broom.
  4. Allow the primer to dry to a thin, slightly tacky film (min. 2 hours, max.12 hours). Install 3.4 galvanized, expanded diamond metal lath mesh to the wood subfloor, stapling approximately 6 inches to prevent the mesh from floating. Overlap adjacent pieces of lath mesh approximately 2”.
  5. It is time now to install Param 5500. It is mixed in 2-bag batches at one time. For each bag, add 5.0 quarts of cool, potable water. Mix for at least 3 minutes with a heavy duty drill mixer (minimum 650rpm) to obtain a lump-free mix. Install at no less than 3/8” thickness over the highest point in the floor.
  6. Protect the poured Param 5500 from excessive heat or draft conditions during the curing process. Turn off all forced ventilation and radiant heating systems. Protect for up to 24 hours after completed installation. The floor can be walked on in 3-4 hours. However, if the surface is colored using a dyes or stains or any other cementitious micro-topping (Skraffino) or covered with epoxy or polyurethane resin coatings or simply sealed with acrylic, epoxy and polyurethane sealers, we recommend waiting for at least 24 hours. Any other type of floor covering (tiles, VCT, etc.) can be installed after 16 hours.

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