Assess the Size and Depth of the Mold
Before you start cleaning, you need to know whether you are dealing with surface mold or mold that has penetrated the wall material itself. Surface mold sits on top of the paint or drywall and usually looks like a dark stain or fuzzy growth. You can often wipe it away with a cloth. Mold that has grown into the drywall or behind the wall is a different problem — the material itself is compromised and usually needs to be cut out and replaced.
If the moldy area is smaller than 10 square feet (roughly a 3-by-3-foot section), you can handle removal yourself with the right precautions. Anything larger, or any mold behind walls or in crawl spaces, should be handled by a professional mold remediation company. If you see mold in multiple rooms or smell a strong musty odor throughout your home, the problem is likely bigger than surface cleaning can fix.
Key Takeaways
- Small surface mold (under 10 square feet) can be cleaned with a stiff brush, detergent, and a fungicide like diluted bleach or white vinegar, but you must fix the moisture source or it will return.
- Mold growing into drywall cannot be cleaned — the affected section must be cut out and replaced, which usually requires a contractor.
- Wear an N95 mask, gloves, and eye protection when cleaning mold, because spores can irritate your lungs and eyes.
- After cleaning, use a dehumidifier or improve ventilation to keep humidity below 50 percent, or the mold will grow back within weeks.
- If mold returns in the same spot after cleaning, the underlying moisture problem has not been solved and you need to find and fix the leak or condensation source.
Gather Your Safety Gear and Cleaning Supplies
Mold spores become airborne when you disturb them, so protecting yourself is the first step. Wear an N95 mask (not a cloth mask or surgical mask) to avoid breathing spores. Put on nitrile gloves to keep mold off your skin, and wear eye protection — safety glasses or a face shield — because spores irritate eyes. If you have asthma, lung disease, or a weakened immune system, do not do this work yourself; hire a professional instead.
For cleaning, you have two main options. Diluted bleach solution (one part bleach to ten parts water) kills mold on non-porous surfaces like tile or sealed paint. White vinegar (undiluted) works on porous surfaces like drywall and is less toxic to you and your home. You will also need a stiff-bristled brush, a spray bottle, clean rags or paper towels, and a bucket. Open windows and doors to ventilate the room while you work.
Clean Surface Mold with Bleach or Vinegar
Start by spraying the moldy area generously with your chosen cleaner — bleach for hard surfaces, vinegar for drywall or painted walls. Let it sit for 10 to 15 minutes so the fungicide can penetrate. Then scrub the area firmly with your stiff brush, using circular motions to break up the mold growth. Rinse with clean water and dry the wall thoroughly with a clean rag or paper towels.
After cleaning, spray the area one more time with your cleaner and let it air-dry. This second process helps prevent the mold from returning when ready. Do not paint over the area until it is completely dry — usually 24 hours — or you will trap moisture and the mold will grow back under the paint.
Remove Drywall if Mold Has Penetrated the Material
If the mold has soaked into the drywall — meaning the wall feels soft, crumbly, or discolored deep into the material — surface cleaning will not work. The drywall itself is damaged and must be removed and replaced. This is a job for a contractor, not a DIY project, because cutting out drywall releases a large amount of mold spores and requires proper containment and disposal.
To know if you need this step, press on the moldy area with your finger. If it feels firm and the mold is only on the surface, cleaning is enough. If the wall feels soft or spongy, or if you can see the mold has stained deep into the material, call a professional. They will cut out the affected section, treat the framing underneath, and install new drywall.
Find and Fix the Moisture Source
Mold cannot grow without moisture. If you clean the mold but do not fix what is making the wall wet, the mold will return within a few weeks or months. Look for the source: a roof leak above the wall, a plumbing leak inside the wall, condensation from poor ventilation, or water seeping in from outside.
Common moisture sources include bathroom exhaust fans that are not vented outside (they dump humid air into the attic), kitchen vents that do not work, windows that sweat in winter, or gutters that overflow and soak the foundation. If the mold is on an exterior wall, check the caulk around windows and the condition of the siding. If it is on an interior wall, look for leaking pipes or condensation from a cold surface. Once you identify the source, fix it — repair the roof, unclog the gutter, install a proper exhaust vent, or insulate the cold surface. Without this step, you are cleaning the same spot over and over.
Use a Dehumidifier or Improve Air Circulation
Even after you fix the moisture source, the wall may still be damp. Use a dehumidifier to pull moisture out of the air and speed up drying. Set it to maintain humidity below 50 percent — most dehumidifiers have a dial or digital display showing the current humidity level. Run it continuously for at least a week after cleaning, and longer if the wall was very wet.
You can also improve air circulation by opening windows (if the weather allows), running ceiling fans, or leaving a door open to adjacent rooms with better ventilation. In bathrooms and kitchens, run the exhaust fan during and for 20 to 30 minutes after showers or cooking. In basements or crawl spaces, install a permanent dehumidifier or improve ventilation with a fan. The goal is to keep the wall dry so mold cannot return.
Know When to Call a Professional
Call a mold remediation company if the moldy area is larger than 10 square feet, if the mold has penetrated the drywall, if you see mold in multiple rooms, or if you have health concerns like asthma or a weakened immune system. Also call if the mold returns in the same spot after you have cleaned it and fixed the moisture source — this usually means there is a hidden leak or moisture problem you cannot see.
A professional will use specialized equipment to detect moisture behind walls, contain the mold spores during removal, and dispose of contaminated material safely. They can also identify moisture sources you might miss. The cost varies widely depending on the size and location of the mold, but it is worth the expense if the problem is large or recurring.
Frequently Asked Questions
Can I use bleach on drywall?
Bleach is too harsh for drywall and can damage the material. Use white vinegar instead — it kills mold on porous surfaces without weakening the drywall. Bleach works well on tile, grout, and sealed painted surfaces.
How long does it take for mold to come back after cleaning?
If you have fixed the moisture source and kept humidity low, mold should not return. If it does come back within a few weeks, the moisture problem is still there. Check for hidden leaks, poor ventilation, or condensation you may have missed.
Is it safe to paint over cleaned mold?
Only if the wall is completely dry — usually 24 hours after cleaning. If you paint while the wall is still damp, moisture will get trapped under the paint and the mold will grow back underneath. Wait until the wall feels dry to the touch.
What if the mold smell stays after I clean?
A lingering musty smell usually means moisture is still present or the mold is growing in a place you cannot see — inside the wall, in the attic, or under the floor. Run a dehumidifier and check for hidden leaks. If the smell does not fade in a week, have a professional inspect for mold you cannot see.
Do I need to replace insulation if there is mold on it?
Yes. Mold-contaminated insulation cannot be cleaned and should be removed and replaced. This is a job for a contractor, especially if the insulation is in a wall cavity or attic where disturbing it releases many spores.