Mold after a leak: dry it within 24 to 48 hours, and clean it yourself only under 10 square feet

Why speed matters

EPA says mold spores float through indoor and outdoor air, and mold may start growing indoors when they land on a wet surface. It’s impossible to get rid of every spore, but spores won’t grow if moisture isn’t present. [S1]

• The clock starts with the leak. EPA says to dry water-damaged areas and items within 24 to 48 hours to prevent mold growth. [S1]
• After a flood, it can be faster. EPA’s flood cleanup page says mold can grow on wood, drywall, carpet and furniture if they stay wet for more than 24 hours. [S5]
• Mold damages what it grows on. EPA says to act quickly: the longer it grows, the more damage it can cause. [S2]
• It can affect your health. CDC says mold can cause a stuffy nose, sore throat, coughing or wheezing, burning eyes or a skin rash in some people, and people with asthma or mold allergies may react severely. [S6]
• Fix the water, not just the mold. EPA says if you clean up mold but don’t fix the water problem, the mold will most likely come back. [S1]

Small patch or big job

EPA says who should do the cleanup depends on several factors, and one is the size of the mold problem. [S2]

1. Under about 10 square feet. That’s less than roughly a 3 ft by 3 ft patch. In most cases you can handle it yourself. [S2]
2. Over 10 square feet, or a lot of water damage. EPA points to its guide Mold Remediation in Schools and Commercial Buildings, which it says applies to other building types too. If you hire a contractor, pick one with mold cleanup experience, check references, and ask them to follow that guide or other guidelines from professional or government groups. [S2]
3. Sewage or other contaminated water. Call a professional who has experience cleaning buildings damaged by contaminated water. [S2]
4. Mold in the heating and cooling system. If you suspect it, don’t run the system, because it could spread mold through the building. EPA points to its air duct cleaning guide before you do anything else. [S2]
5. Health concerns. EPA says to consult a health professional before starting cleanup. After a flood, it says people with asthma or weakened immune systems should stay away from moldy sites, and children and pregnant people shouldn’t take part in flood cleanup. [S2] [S5]

Cleaning a small patch

1. Stop the water first. Fix plumbing leaks and other water problems as soon as possible, and dry everything completely. [S3]
2. Gear up. EPA suggests an N-95 respirator that fits properly, long gloves that reach the middle of the forearm, and goggles without ventilation holes. Ordinary household rubber gloves are fine with water and mild detergent. With bleach or a strong cleaner, it says to choose natural rubber, neoprene, nitrile, polyurethane or PVC gloves. Don’t touch mold with bare hands. [S1]
3. Scrub hard surfaces. Use detergent and water, then dry completely. [S3]
4. Let go of soaked soft stuff. Absorbent or porous materials like ceiling tiles and carpet may have to be thrown away if they get moldy, because mold can fill their crevices and be hard or impossible to remove. CDC adds that soaked carpet and upholstery that can’t be dried right away should be removed or replaced. [S3] [S6]
5. Don’t paint over it. EPA says not to paint or caulk moldy surfaces. Clean and dry them first, since paint over mold is likely to peel. [S3]
6. Precious items. If something is expensive or sentimental, or you’re unsure how to clean it, EPA suggests a restoration specialist. [S3]

Stains may stay even after the mold is gone. EPA says mold can cause staining and cosmetic damage, and an item may not return to its original look. [S2]

Bleach isn’t the first step

• Remove it, don’t just kill it. EPA says dead mold may still cause allergic reactions, so killing it isn’t enough; it has to be removed. It doesn’t recommend bleach or other biocides as a routine part of mold cleanup. [S4]
• If you do use bleach. CDC says mold can come off hard surfaces with household products, soap and water, or a bleach solution of no more than 1 cup of household laundry bleach in 1 gallon of water. Open windows and doors, and wear rubber boots, rubber gloves and goggles. [S6]
• Clean before you disinfect. EPA’s flood page says to thoroughly clean a surface with clean water and detergent before using any disinfectant or sanitizer. [S5]
• Never mix. Never mix bleach with ammonia or other cleaners. EPA warns toxic fumes could form, and CDC calls the result a poisonous gas. Ventilate and follow the product’s instructions. [S4] [S6]

Smell it but can’t see it

EPA says to suspect hidden mold if a home smells moldy but you can’t find the source, or if there’s been water damage and people in the home report health problems. It can hide behind drywall, wallpaper or paneling, on top of ceiling tiles, under carpet and pads, inside walls around leaking pipes, behind furniture where condensation forms, and inside ductwork. [S1]

• Careful what you pull off. Peeling back wallpaper with mold under it can release a large burst of spores. For a suspected hidden problem, EPA suggests an experienced professional. [S1]
• Testing usually isn’t needed. EPA says sampling is unnecessary in most cases when mold is visible, and there are no EPA or other federal limits for mold. CDC says it doesn’t recommend mold testing: whatever the type, you need to remove it. [S1] [S6]

Keep it from coming back

• Watch the humidity. EPA says keep indoor humidity below 60% if you can, ideally 30 to 50%, and a humidity meter from a hardware store can measure it. CDC says no higher than 50%, with an air conditioner or dehumidifier to help. [S1] [S6]
• Vent moisture outside. Vent clothes dryers and stoves outdoors, and run the bathroom fan or open a window when you shower. Use exhaust fans or open windows while cooking or running the dishwasher. [S1] [S6]
• Dry condensation fast. Moisture collecting on windows, walls or pipes can be a sign of high humidity. Dry the wet surface quickly, cut the moisture source, and cover cold water pipes with insulation. [S1]
• Outside the house. Clean and repair gutters, make sure the ground slopes away from the foundation, and keep air conditioner drip pans clean and drain lines flowing. [S1]
• Renting? EPA says report every plumbing leak and moisture problem to your building owner or manager right away. [S1]
• Bathrooms. Mold that keeps coming back in the shower usually stays down with more ventilation and more frequent cleaning, EPA says. [S2]

Running a humidifier this winter? Our humidifier guide covers the 30 to 50% range and cleaning. And a new furnace filter won’t fix mold: our furnace filter guide explains why.

After a flood

Flood water brings its own hazards, so EPA treats it as a bigger job than a pipe leak. [S5]

• Clean gently before fans. If you can already see mold, gently clean the mold you can see before starting fans or dehumidifiers, so the fans don’t spread it. [S5]
• Drying takes time. EPA says drying usually takes several days to weeks. Don’t seal wall cavities or paint anything that was wet until it’s dry inside. [S5]
• Check with a meter. EPA says materials such as walls, cabinets and flooring should read 15% or less on a moisture meter before they’re refinished. [S5]
• Test the slab. Fasten the edges of a clear plastic sheet to the concrete slab and wait about 16 hours. Moisture on the plastic means it’s still too wet to replace the flooring. [S5]
• Generators outside. EPA says run portable generators only outdoors and at least 20 feet from buildings. Our generator placement guide has more. [S5]

Facing flood water on the way home? Our flooded road guide covers what to do before you get there.

What to do now

Pick how big the problem is and where the water came from. The answer puts the EPA and CDC steps from this page in one place. [S2] [S5]

Leak and mold checklist

Quick answers