Check how far the rot goes
Rot often looks smaller than it is. Start by probing the wood with an awl or a small, sharp screwdriver. Sound wood resists the point. Rotted wood feels soft or punky, and the point sinks in. Brown rot often breaks into blocky, cube-like pieces, while white rot tends to look pale and stringy. Probe the wood around the visible damage too, and mark where the soft wood ends.
Fix the moisture source first
Wood only rots when it stays wet. Decay fungi generally need wood moisture content above about 20 percent, and they do best when the wood is close to saturation. Dry wood doesn’t rot. That makes the moisture source the first thing to fix. Common sources include legs standing in damp soil, a planter that leaks onto a piece, standing water on a surface, and unsealed end grain. If the source isn’t fixed, most repairs will fail.
Can you fix rotted wood without replacing it?
Often, yes, if the rot is limited to a part that doesn’t carry much load, such as the edge of a board, a decorative panel, or a small section of rail. The method is to remove all the soft wood, dry the area, strengthen the sound wood that’s left, and rebuild the missing shape with epoxy.
For a leg or another load-bearing part where a lot of wood has rotted, a filler alone won’t restore strength. A splice or a replacement part is usually the better choice.
Step by step: remove, dry, consolidate, fill, shape
- Remove the soft wood. Cut back to sound wood with a chisel, a carbide burr, an oscillating tool or an awl. Wear a dust mask or respirator while you do this, because rot dust carries fungal spores.
- Dry the area. Let the wood dry well before you treat it. Many product labels suggest getting the moisture content under about 15 percent, but check the one you’re using.
- Optionally, treat it with a borate. Some restorers brush on a borate, such as disodium octaborate, to help kill remaining fungi. Borates wash out of outdoor wood unless it’s sealed, so they suit protected pieces best.
- Consolidate. Brush on a low-viscosity penetrating epoxy, the kind sold for consolidating rotted wood, and keep applying it until the wood stops soaking it up. This hardens the fibers that are left. The same approach is used on wood weakened by beetles, as in how to repair woodworm damage.
- Fill the voids. While the consolidant is still tacky, press an epoxy putty into the gaps. For a large void, pack in a piece of sound wood first and fill the rest with epoxy.
- Shape and finish. When the epoxy has fully cured, shape it with rasps or files and then sand. Cure times vary, often around a day, so follow the label.
Epoxy doesn’t take stain. Paint it, or color it with tints before it sets, and then add grain marks if you want the repair to blend in.
What filler works on rotted wood
Epoxy putty is the usual choice for rotted wood. It bonds to sound wood, holds its shape, and is strong enough for a load-bearing repair. Standard wood fillers are designed for small, sound holes, and they tend to fail when the surrounding wood is still soft or moves with humidity.
Wood hardener is sometimes confused with filler. It soaks into soft wood and firms it up, but it doesn’t fill anything, so you still need a filler on top. Epoxy usually needs a warm room to cure properly, often about 60°F (15°C) or warmer, so check the label before you start.
Can you put wood filler over rotted wood?
Not as a lasting repair. Filler sticks best to sound wood. Soft wood left in place keeps taking up moisture and can push the repair out. Remove all the soft wood before you fill it. If you’re dealing with a small patch of sound wood rather than rot, a standard wood filler may be enough, but that’s a different job.
Can you stop rot once it has started?
You can stop rot from spreading, but the damage that’s already there won’t reverse. The goal is to remove the soft wood, dry the area, fix the moisture source, and keep the wood dry. Fungi need moisture to grow, so a dry, protected area won’t keep rotting. Borates and hardeners can help kill or firm the remaining wood, but they don’t bring back the strength that’s been lost.
When to splice or replace a structural part
Consider a splice or replacement when the rot is in a leg, a rail, or a joint that holds weight. A scarf joint is a long, shallow splice, and a slope of around 1 in 8 is a common guide, though the right angle depends on the design. If most of a part has rotted, replacing it can be simpler than splicing.
On antique furniture, original wood is worth keeping where you can, as antique furniture restoration explains. For a valuable piece, a restorer can advise before you cut anything.
Preventing rot from coming back
- Seal exposed end grain, which soaks up water quickly.
- Add glides or feet to lift legs off wet floors or damp ground.
- Keep the finish in good repair. Cracked paint or varnish lets water in.
- Don’t paint over soft wood. Paint hides the rot and can trap moisture.
Safety
- Wear a dust mask or respirator when you’re digging out rot, because fungal spores and mold can irritate the lungs.
- Epoxy is a skin sensitizer. Wear nitrile gloves and work in a ventilated space.
- Borates are low in toxicity, but don’t ingest them, and wear gloves when you handle them.
If you’re working on a piece that’s part of a larger repair, the wood furniture repair overview shows where rot fits among other kinds of damage. For legs that are loose rather than rotted, see repairing antique furniture legs.