Black mold on wood can be cleaned with vinegar, hydrogen peroxide, or a borax solution if the wood is not structurally damaged
Black mold grows on wood when moisture sits on the surface for days or weeks. The mold itself is a living fungus that feeds on the wood fibers. You can remove it with household cleaners, but the real problem is the moisture underneath — if you do not fix that, the mold will return within weeks.
The cleaning method depends on how deep the mold has gone. Surface mold (the kind you can wipe off) responds to vinegar or hydrogen peroxide. If the wood is soft, spongy, or crumbles when you press it, the mold has eaten into the structure and the wood should be replaced, not cleaned.
Key Takeaways
- Surface black mold on wood can be cleaned with white vinegar, 3% hydrogen peroxide, or a borax solution applied with a brush or cloth.
- Do not paint or seal over mold — it will trap moisture underneath and the mold will spread faster.
- After cleaning, you must find and stop the moisture source or the mold will return within weeks.
- If the wood is soft, spongy, or the mold has penetrated deeper than a quarter-inch, the wood should be replaced rather than cleaned.
- Wear gloves and eye protection when cleaning, and work in a ventilated space to avoid breathing mold spores.
When to clean versus when to replace the wood
Press the moldy area with your fingernail or a flathead screwdriver. If the wood is hard and the mold sits only on the surface, cleaning will work. If the wood is soft, spongy, or your tool sinks in, the mold has rotted the wood from inside and it cannot be saved by cleaning.
Check the edges of the affected area too. If mold extends more than a few inches in any direction, or if it covers more than about one square foot, the wood is likely compromised deeper than you can see. In basements, crawlspaces, or bathrooms where wood stays damp, replacement is usually the safer choice.
Wood that has been wet for more than 48 hours is at risk of structural damage. If you do not know how long the mold has been there, assume the wood is damaged and plan to replace it. A rotted floor joist or wall stud can fail without warning.
Cleaning surface mold with vinegar
White vinegar is the gentlest option and works on most surface mold. Pour undiluted white vinegar (5% acidity) into a spray bottle. Spray the moldy area until it is wet but not dripping. Let it sit for one hour, then scrub with a stiff brush. Wipe away the loosened mold with a damp cloth and let the wood dry completely.
Vinegar does not kill mold spores that have gone deep into the wood, but it stops the mold from spreading on the surface. It also does not leave a toxic residue, so it is safe to use on wood you will touch or that is near food. The smell fades as the wood dries.
If the mold returns in the same spot within a week, the wood is still wet and vinegar alone will not solve it. Move to the moisture source before cleaning again.
Using hydrogen peroxide for faster results
3% hydrogen peroxide (the kind sold in drugstores) kills mold faster than vinegar and penetrates slightly deeper into the wood. Spray it on the moldy area, let it sit for 10 minutes, then scrub with a stiff brush. Wipe the area dry with a cloth.
Hydrogen peroxide is stronger than vinegar but still safe for indoor use. It breaks down into water and oxygen as it dries, leaving no chemical residue. Do not use industrial-strength hydrogen peroxide (anything above 3%) on wood — it will bleach the surface and can damage the fibers.
Wear gloves and eye protection when using hydrogen peroxide. If you splash it in your eyes, rinse when ready with water for at least 15 minutes and call poison control or seek medical attention.
Borax solution for stubborn mold
Borax is a mineral powder that kills mold spores and prevents regrowth for several weeks. Mix one cup of borax with one gallon of water. Brush or spray the solution onto the moldy wood and let it soak for 10 to 15 minutes. Scrub with a stiff brush, then wipe the area dry.
Do not rinse the borax off — let it dry on the wood. The residue will continue to prevent mold growth as long as the wood stays dry. Borax is toxic if swallowed, so wash your hands after use and keep it away from children and pets.
Borax works best on wood that will stay relatively dry, like exterior siding or a basement wall that is not in standing water. If the wood is in a constantly damp environment, borax will slow the mold but not stop it permanently.
Finding and fixing the moisture source
Mold returns because water is still reaching the wood. Look for the source: a roof leak, a plumbing leak, condensation from poor ventilation, or water seeping up from the ground. Until you stop the water, cleaning is temporary.
In bathrooms, run the exhaust fan during and for 30 minutes after showers. In basements, check for cracks in the foundation, gaps around pipes, or standing water. On exterior wood, check the gutters, downspouts, and grading around the foundation. Water should slope away from the house, not toward it.
If you cannot find the source, call a plumber or a foundation inspector. A small leak that you cannot see will cost far more to fix later as rot spreads through the framing.
What not to do when cleaning black mold
Do not paint or seal over mold. Paint traps moisture underneath and the mold will spread faster. Do not use bleach on wood — it does not kill mold spores deep in the fibers and it can damage the wood surface. Do not sand the moldy area, because sanding releases mold spores into the air and you will breathe them in.
Do not use a pressure washer on interior wood or on wood that is already soft. The force of the water will drive moisture deeper into the wood and make the rot worse. Pressure washers are safe only on hard exterior wood like treated deck boards.
Do not assume the mold is gone because you cannot see it. Mold can regrow from spores that are still in the wood. If the area stays damp, the mold will come back even if you cleaned it thoroughly.
When to call a professional
If the moldy area is larger than a few square feet, if the wood is soft or crumbling, or if the mold is in a structural area like a floor joist or wall stud, call a mold remediation company or a contractor. They have equipment to dry the wood thoroughly and can assess whether the wood can be saved or must be replaced.
If the mold is in a crawlspace or attic, or if you suspect a hidden leak, a professional inspection is worth the cost. Mold in those spaces can spread for months without you noticing, and by the time you see it, the damage may be extensive.
Your homeowner's insurance may cover mold removal if it is caused by a sudden event like a burst pipe or roof leak. Check your policy and contact your insurer before you hire someone. Some policies exclude mold damage or limit coverage to a certain amount.
Frequently Asked Questions
Can I use bleach to kill black mold on wood?
Bleach does not penetrate wood fibers effectively and can damage the wood surface. Vinegar, hydrogen peroxide, or borax are better choices for wood. Bleach is useful for mold on tile, grout, or non-porous surfaces, but not for wood.
How long does it take for mold to come back after cleaning?
If the moisture source is still present, mold can return within one to three weeks. If you have fixed the moisture problem and the wood stays dry, mold may not return at all. The key is keeping the wood dry, not just cleaning it once.
Is black mold on wood dangerous to breathe?
Black mold produces spores that can irritate your lungs and sinuses, especially if you have asthma or a weakened immune system. Wear a dust mask rated N95 or better when cleaning mold, and work in a ventilated space. If you have respiratory problems, let someone else do the cleaning.
Can I just sand off the mold instead of using chemicals?
Sanding releases mold spores into the air and you will inhale them. It also does not kill the mold — it just removes the visible growth. Use a wet cloth or a chemical cleaner instead, which keeps spores from becoming airborne.
What if the mold is on wood inside my walls?
Mold inside walls is a sign of a serious moisture problem, usually a leak in plumbing or the roof. You cannot clean it without opening the wall, and by the time you see mold on the surface, the wood inside is likely rotted. Call a contractor or mold remediation company to find the leak and assess the damage.