How to Use Two-Part Epoxy to Fill Rotted Trim

Rot happens, even to the best of houses. Your exterior trim is particularly vulnerable, and it doesn’t have to be very old—all it takes is wood, water, and warmth. 

Two-part epoxy is a versatile solution that can repair rotted wood and restore your trim’s integrity. It consists of a resin and a hardener that, when mixed, make a strong, durable filler. This guide will teach you how to use it.

Identifying Rotted Areas

Before you can fix rot, you have to find it. Check out horizontal areas that don’t drain well, joints that dry slowly, and any wood that’s close to the ground or to masonry. If you see these signs, you may have rot to reckon with:

• Cracked, peeling, or blistering paint
• Discolored or darker wood
• Soft or spongy wood when pressed with a screwdriver
• Visible fungal growth

Preparing the Rotted Area for Repair

Start the repair process by removing soft and decayed wood. Claw out loose material with a hammer, and remove the remaining rotting wood with a die grinder or Dremel rotary tool. Continue until the rot is gone. Then, allow the area to dry completely.

For an effective epoxy repair, the freshly exposed wood has to be sound and dry with less than 18% moisture content. Before you continue, use a moisture meter to make sure your wood is dry enough.

In the video below, general contractor Tom Silva explains how to repair rotting wood with epoxy.

Applying the Epoxy

Now that the area is prepared, it’s time to apply the epoxy. 

Injecting Borate Wood Preservative

Before applying epoxy, treat the wood with a borate-based preservative. This penetrates the wood and minimizes the chance of decay in the future. 

Drill small holes about halfway into the wood and inject the preservative into the holes. Allow it to soak according to the package directions.

Applying Epoxy Primer

Priming guarantees a strong bond between the wood and epoxy. Mix the primer according to the manufacturer’s instructions and brush it onto the exposed wood. Wait about 15 minutes for the liquid to penetrate, then wipe off any excess with a clean paper towel.

Mixing and Blending the Epoxy

Proper mixing impacts the epoxy’s effectiveness. Dispense equal parts of resin and hardener onto a plastic mixing board and blend them with a plastic putty knife until the color is uniform. Epoxy doesn’t stick to hard plastic surfaces, so you can clean the board and knife and reuse them later. However, you should still work quickly since the mixture starts to set within 30–45 minutes.

Sculpting the Epoxy Filler

Next, use the same plastic putty knife to apply the epoxy mixture to the prepared area and shape it to match the surrounding trim profile. Overfill slightly to allow for sanding, but smooth the surface as much as possible. 

Depending on the weather, the epoxy will remain workable for about 30 to 45 minutes. It may last longer on cool days and shorter on hot days. Avoid touching or disturbing the repair while the filler cures.

Finishing and Protecting the Repair

Epoxy breaks down in sunlight. Once it’s cured, you’ll need to finish the repair the next day by giving it a coat of paint. 

First, sand the epoxy. Start with 80-grit sandpaper to remove major imperfections, then move up to 100-grit, and finish with 220-grit for a smooth surface. 

Next, apply an acrylic primer suitable for exterior use, followed by two coats of 100-percent acrylic paint that matches the color of the trim. Allow time to dry between each coat.

Preventing Future Rot in Exterior Trim

Regular maintenance can prevent rot in the first place. Follow these tips to protect your home’s trim:

• Inspect trim annually for signs of damage or decay.
• Make sure your gutter system is in good working order and cleaned regularly to direct water away from your exterior walls.
• Touch-up paint and reseal the trim as necessary to prevent moisture penetration.

When To Call a Professional

While many homeowners can successfully repair rotted trim with epoxy, you may still need professional help in some situations. Call a trusted local contractor if the repair goes beyond surface trim to affect your home’s structural integrity or if the trim is in a spot you can’t reach yourself. 

Our Conclusion

Two-part epoxy is a versatile and effective solution for repairing rotted exterior trim. With a few simple chemicals and tools, you can restore its appearance and protect it from further damage. Remember to address the underlying causes of rot and implement preventative measures to keep your trim in good condition.