How to remove mold and mildew from wood

How to remove mildew and mold from wood

1. 1

   Protect yourself and size it up

   Put on rubber gloves, eye protection and an N-95 respirator. If the mold covers more than about 10 square feet, came from sewage or flood water, or is inside walls or under floors, stop and get professional advice.

   Why: The EPA and Georgia's extension service limit do-it-yourself cleanup to small areas from clean water, and protective gear keeps spores out of your lungs and eyes.

2. 2

   Remove loose growth outdoors

   Move furniture outside if you can. Vacuum the moldy surface with a HEPA vacuum or brush it off gently with a soft brush, including undersides, drawer interiors and the back panel.

   Why: Removing the powdery growth first keeps spores from being smeared around by the wet cloth. Georgia's guide specifies a HEPA vacuum, not a standard one.

3. 3

   Wipe with mild detergent on a damp cloth

   Mix a little mild detergent into water. Wring a cloth out until it's barely damp and wipe the moldy area a small section at a time, then wipe again with a cloth dampened in plain water.

   Why: This is Georgia's method for hard-surfaced furniture. Detergent lifts the growth and the soil it feeds on, and a barely damp cloth keeps water from soaking into the wood or the finish.

4. 4

   Dry each section immediately

   Dry the area with a clean soft cloth as soon as you finish wiping it.

   Why: Standing water damages wood finishes and raises the grain, and leftover moisture is exactly what mold needs.

5. 5

   Dry slowly in a ventilated room

   Let the piece finish drying indoors with a fan or dehumidifier, out of direct sun. Open drawers and doors so air reaches the inside.

   Why: Wood dried fast in the sun can warp and crack. NC State notes mildew keeps growing as long as the wood's moisture content stays above about 20 percent.

6. 6

   Check again in a few days

   Look the piece over after two or three days, especially underneath and inside. Keep indoor humidity below 60 percent.

   Why: Georgia's guide warns mold can regrow in 2 to 3 days; if it does, the moisture problem hasn't been solved.

Why mold grows on wood, and why some stains stay

Mold and mildew are fungi that need moisture and something to feed on. Wood itself is food, and so is the dust, oil and old polish on its surface. That makes mildew a biological stain: living growth plus the discoloration it leaves. The EPA's rule of thumb is that materials dried within 24 to 48 hours of getting wet usually don't grow mold.

The finish decides how far it goes. On a sealed, intact finish, mold mostly sits on the surface and wipes off. On bare wood, worn finishes and the unfinished backs and undersides of furniture, it can grow into the grain. The EPA notes that mold in porous materials can be difficult or impossible to remove completely, and a dark stain left after cleaning usually means the wood or finish needs sanding and refinishing.

Why the finish limits what you can use

Many furniture finishes are sensitive to solvents and water. Shellac is applied dissolved in alcohol, so alcohol softens it, and the National Park Service's furniture conservators warn that detergents can leave a hard-to-remove film on fine finishes. That's why the method uses only a little mild detergent on a well-wrung cloth, and why every product gets a hidden-spot test first. For more on mildew across surfaces, see the mildew stain guide.

By situation

Mildew on finished wood furniture

After the detergent wipe, NC State's flood-furniture guide suggests mineral spirits on mildewed surfaces. Test on a hidden spot first, use it on a cloth in a ventilated area, and stop if the finish softens.

Antique or valuable furniture

Brush off loose growth outdoors and consult a furniture conservator or restorer. Cleaning can damage original finishes, and Georgia's guide suggests a specialist for expensive or sentimental items.

Bare wood, decks, trim and framing

Unfinished wood absorbs water, so scrub with detergent and water and dry it fast with fans. If a dark stain remains in the grain after it's dry, light sanding may remove it. Wood framing should be at or below 15 percent moisture before wallboard goes back up, according to Georgia's guide.

Flood-damaged furniture

Take it outside, remove drawers, doors and back panels, and hose off mud. Dry it slowly in a ventilated area, not in the sun; NC State says this can take weeks or months. Solid wood with a cloudy finish or loosened joints can often be repaired by a cabinetmaker.

Musty smell inside drawers

Wipe the inside with the detergent solution, dry it, and leave the drawers open in a dry, ventilated room for several days. Check that the piece isn't against a damp wall.

What not to do

• Don't soak or hose down finished furniture to clean it. Wood swells and shrinks as it gets wet and dries, which loosens joints, warps boards and clouds the finish.
• Don't dry wet wood in direct sun or with high heat. Fast drying makes wood warp and twist.
• Don't rely on chlorine bleach. The EPA doesn't recommend bleach as a routine mold cleanup step; removing the growth and drying the wood matter more. Bleach can also damage finishes.
• Don't mix bleach with ammonia or vinegar. Both combinations release toxic gases.
• Don't brush mold off indoors without protection. It puts spores into the air of the house.

Other methods that work

White vinegar

Often suggested for mildew on wood. No extension or government source in this guide recommends it, so it's traditional, with weak evidence.

Caution: It's an acid that can dull some finishes. Test first, and never use it with bleach.

Professional refinishing

When mold has stained the wood itself, a refinisher can strip, sand and treat the surface, then refinish it.

Caution: On antiques, refinishing can lower value; ask a conservator first.

Stain still there?

A dark gray or black stain remains after cleaning

The mold has grown into the wood or the finish. If the surface is dry and no new growth appears, the stain is cosmetic; sanding and refinishing are the way to remove it.

The mold came back within days

The wood or the room is still too damp. Lower humidity with a dehumidifier, move the piece away from exterior walls, clean it again and dry it thoroughly.

The finish turned cloudy or white

Moisture got into the finish. Let it dry slowly out of the sun. White spots or cloudiness that persist after drying may need refinishing.

Safety

• Wear gloves, eye protection and an N-95 respirator when cleaning mold.
• Mineral spirits are flammable: ventilate and keep away from flames.
• People with asthma, allergies or breathing problems should leave mold cleanup to someone else.

Never mix cleaning products; see chemicals you must never combine.

Questions

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