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How to Identify and Repair Rotting Wood

General contractor Tom Silva takes host Kevin O’Connor through the causes of wood rot, how to avoid it, and what to do when it occurs.

Host Kevin O’Connor and general contractor Tom Silva discuss identifying wood rot and what to do about it. After discussing some of the key ways to keep wood from rotting, like flashing and avoiding ground contact, the two discuss the signs of wood rot.

How to Prevent Wood Rot

For the most part, rotting wood is preventable, but it requires keeping water away from the house as much as possible. This means installing gutters and maintaining them, preventing the wood from coming in contact with the ground, and adequately flashing any openings that water could sneak into.

Also, seal any outdoor wood surfaces like fascia, window sills, and trim with a sealer or primer—don’t forget the backs!

Signs of Rot

It’s important to know what to look for when identifying wood rot.

First, look for peeling paint on wood surfaces. This indicates that water is penetrating the wood. As the sun dries the board, it pulls the water through the wood and separates the paint from the surface.

Also, look for soft, punky wood that flakes off. This is advanced rot and can be a sign of carpenter ants.

Replace or Repair?

If you can replace the rotting wood easily, you should. Just be sure to seal and flash the board, so the rot doesn’t come back. This could be the case for window and door trim, fascia boards, decking, and other wood that’s easily accessible and readily available.

But, replacing a board isn’t always easy. In the case of window or door sills, replacing the rotted wood can be a big job-one that’s not necessary if enough good wood still exists. In that case, it’s better to remove as much of the rotten, compromised wood as possible by scraping, cutting, or sanding before repairing.

Fixing Rotten Wood in Place

Once the rotten wood is removed, you can repair it in place with products explicitly meant for the job. A rotted wood restorer can be applied to the damaged wood to restore its strength before repairing it.

You can then apply a high-quality wood filler with a putty knife to the surface. Most of these wood fillers are two-part formulas, and it’s a good idea to go light on the hardener, not heavy.

When the filler dries, sand it to a smooth, even finish to hide repair before priming and painting.


Tom recommends preventing rot from happening in the first place by ensuring windows and doors are properly flashed, gutters are hung correctly, and water is being diverted away from the building. If a small amount of rot is detected, it’s possible to repair it to keep it from spreading. In the segment, Tom used a combination of wood filler and wood rot restorer manufactured by Bondo, a 3M product.

Tom’s other tools and materials to demonstrate repairing rot, including the putty knife and a palm sander, can be found at home centers.