How to Repair Rotted Wood with Epoxy
Restore structural integrity to rotted exterior wood using liquid hardener consolidant and two-part sculptable epoxy wood filler.
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🧰 Required Tools & Equipment
- ✓ Wood chisel
- ✓ Wire brush
- ✓ Cordless drill with 1/4-inch bit
- ✓ Disposable paintbrush
- ✓ Plastic putty knife or margin trowel
- ✓ Random orbital sander with 80 and 120-grit sandpaper
📦 Materials & Supplies
- ✓ Two-part liquid epoxy wood consolidant/hardener
- ✓ Two-part epoxy wood filler paste
- ✓ Mixing board or plastic sheet
- ✓ Nitrile gloves
- ✓ Exterior acrylic primer
⚠️ Safety Checkpoints & Warnings
- • Wear safety glasses and a dust mask when excavating crumbly rot and sanding cured epoxy.
- • Work in a well-ventilated area and wear chemical-resistant nitrile gloves when mixing and applying liquid consolidant and paste.
📋 Step-by-Step Guide (5 Steps)
Excavate Rotted and Spongy Wood
Dig out all soft, dark, and punky wood fibers using a chisel or stiff scraper. Continue scraping until you strike bright, firm, sound timber across the entire cavity. Clean loose dust and debris out of the pocket with a stiff wire brush.
- • Cavity walls consist entirely of pale, solid, splintering wood
- • No dark brown or black spongy fibers remain in the pocket
- • Leaving soft wood behind to save time, which traps moisture and causes failure
Drill Epoxy Infiltration Holes
Drill a series of 1/4-inch holes spaced roughly 1 inch apart around the perimeter and base of the excavated cavity. Angle the bit downward and drill about 1/2 to 3/4 inch into the sound surrounding wood. Vacuum or blow out all wood shavings from the holes.
- • Clean grid of angled holes surrounding the void
- • All drill dust completely removed from holes and cavity
- • Drilling entirely through the back of the trim or board
Apply Liquid Epoxy Consolidant
Mix equal parts of liquid consolidant resin and hardener according to manufacturer ratios. Brush the liquid liberally into the drilled holes and across all exposed end-grain surfaces. Reapply until the wood is fully saturated and cannot absorb more liquid.
- • Glossy, wet-sheen surface across all bare wood fibers
- • Drill holes filled and slowly draining liquid into deep grain
- • Applying paste filler onto dry wood without using consolidant first
Mix and Pack Two-Part Epoxy Paste
Measure equal parts of epoxy resin and hardener paste onto a smooth board and knead them together with a putty knife until color is completely uniform. Press the mixed paste firmly into the cavity bottom, eliminating all air pockets. Build up the patch so it sits roughly 1/8 inch higher than the surrounding profile.
- • Evenly colored, streak-free epoxy putty filling the entire void
- • Putty surface sits slightly proud of adjacent wood faces
- • Leaving visible streaks in the putty, indicating incomplete chemical mixing
Shape, Sand, and Prime the Repair
Allow the epoxy to cure fully to a rock-hard state, usually 4 to 8 hours. Sand the patch flush with the surrounding wood using 80-grit abrasive, then smooth the profile with 120-grit paper. Wipe away all dust and apply a coat of exterior primer over the repair.
- • Seamless, flat transition from cured epoxy to adjacent wood with no ridge felt by hand
- • Opaque, uniform primer coat covering the entire repair and overlapping edges
- • Sanding before the epoxy is fully cured, clogging the sandpaper with gummed paste
Credit: inspired by an original tutorial by This Old House — watch the original on YouTube.
Don’t have everything?
- No Random orbital sander? Hand sanding block with 80-grit and 120-grit sandpaper
- No Wood chisel? Stiff 5-in-1 painter's tool or flathead screwdriver