Surface Preparation for Wood Substrates
Epoxy.com Technical Bulletin
1. General Requirements
Epoxy flooring systems can be successfully installed over properly prepared wood substrates, but only when the correct materials, plywood grades, and reinforcement procedures are used. Wood moves, flexes, absorbs moisture, and expands far more than concrete — so preparation must be done carefully and correctly.
Epoxy.com requires the use of ¾-inch AC Exterior Grade Plywood (sanded one side) with an exterior glue line for new construction. Interior plywood must not be used. Marine-grade plywood must not be used, as moisture-repellent treatments interfere with bond and may cause darkening. Fire-retardant plywood is not recommended unless specifically tested and approved by Epoxy.com.
Where additional reinforcement is needed, ½-inch fiber-cement backer board (Hardie-type board) may be installed over a minimum ½-inch plywood base.
All wood substrates must be structurally designed to limit deflection to L/360.
All surfaces must be clean, dry, sound, and free of wax, varnish, paint, oil, or contaminants.
2. Existing Wood Floors (Renovation Overlays)
- Clean and secure the original wood floor to its joists. Tighten or replace loose fasteners.
- If the original floor is structurally sound, install ½-inch AC Exterior Grade Plywood over it, staggered for strength.
- If not sound or not cleanable, install ¾-inch AC Exterior Grade Plywood over the entire surface.
- Ensure all plywood is free of wax, varnish, or coatings.
- Use exterior-grade glue between plywood layers.
- Fasten using screws spaced 6 inches on all panel edges and supports.
- Stagger joints, fill joints with Epoxy Gel – Product #2704, and reinforce each joint with fiberglass cloth embedded in resin. You may treat individual joints or overlay the entire area.
- Lightly sand the surface and vacuum thoroughly.
- Prime the surface; wood often requires two coats due to porosity.
- Install the selected Epoxy.com flooring system.
3. New Construction (Plywood on Joists)
- Use ¾-inch AC Exterior Grade Plywood (sanded one side) over joists.
- Ensure plywood is clean and free of wax, varnish, or surface treatments.
- Fasten plywood using screws at 6-inch centers on edges and supports.
- Stagger all panel joints and fill using Product #2704, then reinforce with fiberglass cloth.
- Lightly sand to promote adhesion and vacuum thoroughly.
- Prime with the Epoxy.com primer system (typically two coats).
- Install the appropriate epoxy or flooring system.
4. Installing Fiber-Cement Board Over Wood
Fiber-cement board may be used to reinforce or level an existing plywood surface. Acceptable configuration:
- ½-inch fiber-cement board installed over minimum ½-inch plywood
- Fasten securely per manufacturer instructions
- Fill seams with #2704 and reinforce with fiberglass cloth before priming
5. Flexible Membrane Reinforcement
Where movement, vibration, or expansion is expected, reinforce using Product #32 Flexible Epoxy Membrane with fiberglass cloth.
Standard Method:
- After priming, apply 32–40 mils of Product #32 over plywood joints (12-inch width) or entire floor.
- Embed fiberglass cloth into the wet resin.
- Allow to cure before installing flooring.
Enhanced Method:
- Apply first coat of Product #32 and allow to cure.
- Apply second coat of #32 or #2704 at 15–20 mils.
- Embed and saturate fiberglass cloth for maximum tensile strength.
6. Primer Selection
Wood substrates require strong bonding and full sealing:
- Primary Primer: Product #12 — strongest chemical resistance
- Alternate Primer: Product #899 — excellent as a general purpose primer
- Most wood substrates require two primer coats to fully seal the surface.
7. Summary of Requirements
- Use ¾-inch AC Exterior Grade Plywood (sanded one side) for new work.
- Minimum ½-inch plywood plus ½-inch cement board allowed for overlays.
- Structural deflection must not exceed L/360.
- Fill joints with Product #2704 and reinforce with fiberglass cloth.
- Use Product #32 for flexible membrane applications.
- Prime with #12 or #899, typically two coats.
- Surface must be clean, dry, and vacuumed before coating.