Even when wood is adequately protected, rot and decay find a way to get in and weaken wood. It might be decking, columns or trim, interior flooring, or anywhere else wood and water get together. Catch it early, patch it, stop it from progressing, and then take some measures to prevent it from happening again.
Moisture is the Culprit
Rot and decay occur naturally in the presence of moisture and oxygen. It's more likely to be found in a moist area, such as a bath or laundry room, but might be anywhere. You might notice it in cracks, seams or anywhere water penetrates. Rot is common alongside boards, behind caulking and around window and door trim, sills and thresholds.
Lots of common products are available for exterior rot repair, but two-part epoxy penetrates deeper than most of them, and has one of the best track records. It's a two-part formula that can be shaped or sanded after it dries.
Repair the Rot
Remove rot with a sharp knife or chisel. Scrape and cut away the soft, rotted wood, removing it to reveal only bare, dry wood. Rot is black or discolored, so keep scraping and cutting until you see the natural amber color of sound wood.
Clean the scraped area with a stiff, wire brush. Epoxy works more efficiently when, fibers, soft wood or old paint are removed. Work the brush aggressively to smooth the area, and then remove any dust, dirt, chips and debris.
Mix equal portions of part A and part B together on a piece of scrap wood using a flat stick. Epoxy begins to thicken in minutes. You have about 30 minutes before it gets too hard. When the mixture is the consistency of soft dough, you're ready to use it.
Trowel the dough-like epoxy into the scraped out opening with a putty knife. When the area is full, apply more and force it down to compress it into a dome shape. Allow the epoxy to dry for at least four hours. Overnight is best.
Shape the dried epoxy with a wood file as needed to conform to profiles or corners, or use a sanding block with 100-grit sandpaper to sand it flush with the surrounding wood. Add paint, stain or a clear top coat as needed.
Alternatives to Epoxy
Simple options to rot repair include wood filler and wood putty. These products come in a tub or tube, and can be used for smaller repair jobs. Some fillers contain silicone and dry slightly flexible to move with the wood. The putty category dries hard, similar to epoxy, won't penetrate as deep, but is easier to use.
After repairs are finished, take precautions to prevent it from happening again. If caulking has allowed water to penetrate where it shouldn't, strip it off and replace it with exterior, acrylic latex caulking. Inspect ceilings, door and window trim, under cabinets with sinks, in bathrooms or wherever water is channeled onto wood. Re-engineer it if possible to keep the water at bay. Repair leaks in plumbing or other fixtures. You can also replace moldings and trim in high-moisture locations, such as bath and laundry rooms, by replacing it with PVC, vinyl or other water-resistant moldings.
Pressure-treated wood is typically thought of as an exterior treatment to preserve wood, and prevent rot, but it hasn't always been thought of as safe for interior use. But a safe, non-toxic interior and exterior treatment for wood has emerged. Borates are naturally occurring minerals found in rocks, water and living organisms. Borates can be applied with a common garden sprayer, and not only defends from rot, but from termites as well. Mix it with water, per product instructions, and apply it to structural studs, beams or anywhere you open a wall or floor to reveal wood.