When to clean mold yourself and when to call a professional
You can remove mold from drywall yourself if the affected area is smaller than 10 square feet — roughly a 3-by-3-foot section. Anything larger than that usually means the mold has gone deep into the drywall's core, and removing it requires replacing the entire sheet. If the mold is near your HVAC system, electrical wiring, or insulation, or if anyone in your home has asthma or a weakened immune system, call a mold remediation contractor instead. The spores released during removal can trigger serious reactions.
Small patches of surface mold on drywall are almost always caused by moisture — a leak, condensation, or high humidity in a bathroom or basement. Before you clean, you must stop the moisture source, or the mold will return within weeks. If you cannot identify where the water is coming from, have a plumber or contractor inspect the area first.
Key Takeaways
- Mold smaller than 10 square feet can be cleaned with a stiff brush, white vinegar or diluted bleach, and a damp cloth, but only after you stop the moisture source.
- Drywall is porous and absorbs water; if mold has been present for more than a few weeks or covers an area larger than 10 square feet, the drywall must be replaced, not cleaned.
- Wear an N95 mask and gloves during cleaning to avoid breathing spores, and ventilate the room by opening windows and running a fan toward the outside.
- After cleaning, keep the area dry by fixing leaks, improving ventilation, and using a dehumidifier if humidity stays above 50 percent.
Prepare the room and protect yourself
Before you start, open all windows in the room and position a box fan in one window facing outward to pull air out of the space. This prevents spores from spreading to other rooms. Put on an N95 mask (the kind rated for particles, not just dust) and disposable gloves. If the mold is in a bathroom, turn off the bathroom exhaust fan if it vents into the attic rather than outside — you want air moving out the window, not into hidden spaces.
Lay newspaper or plastic sheeting on the floor beneath the moldy area to catch drips and spores. Do not use a regular household vacuum to clean up mold debris — vacuums spread spores into the air. You will sweep or wipe everything into a trash bag instead.
Clean the surface with vinegar or diluted bleach
For most small mold patches, white vinegar works as well as bleach and is safer to handle. Pour undiluted white vinegar into a spray bottle and spray the moldy area until it is wet. Let it sit for one hour, then scrub with a stiff-bristled brush. Wipe away the loosened mold with a damp cloth and let the area dry completely.
If vinegar does not work after two applications, use a diluted bleach solution: one cup of bleach per gallon of water. Spray it on, wait 10 minutes, scrub, and wipe clean. Bleach is stronger but toxic if inhaled, so keep the window fan running and do not mix bleach with ammonia or other cleaners. After cleaning with either solution, wipe the area a second time with a cloth dampened in plain water to remove any chemical residue.
Do not paint over mold or use mold-killing primer as a shortcut. The mold will grow back under the paint within weeks because the moisture problem is still there.
Determine if the drywall needs to be replaced
After you clean the surface, inspect the drywall closely. Press your finger gently on the area — if it feels soft or spongy, water has soaked into the core and the mold extends deeper than the surface. Drywall that has absorbed water for more than a few weeks cannot be fully cleaned and will mold again. In this case, the affected section must be cut out and replaced.
To replace a section of drywall, you will need to cut out the moldy area in a rectangle, remove the damaged piece, and install a new patch. This is a job for a contractor if you have not done drywall work before. The cost varies widely depending on the size and location, but a small patch typically costs between $150 and $400 in labor and materials.
Stop the moisture source or the mold returns
Mold on drywall always means water is getting in. Common sources are roof leaks, plumbing leaks behind walls, condensation from poor bathroom ventilation, and groundwater seeping into basements. Walk around the outside of your home on a rainy day and look for water running down the wall or pooling near the foundation. Inside, check for water stains on the ceiling or walls above the moldy spot, which point upward to the leak.
If the mold is in a bathroom, run the exhaust fan during and for 30 minutes after showers. If there is no exhaust fan, install one or open a window. In basements and crawl spaces, use a dehumidifier to keep humidity below 50 percent. If you find a plumbing leak, have it repaired when ready — do not wait. A small drip can soak drywall in days.
Prevent mold from returning after cleaning
Once you have cleaned the mold and fixed the moisture source, keep the area dry. In bathrooms, wipe down wet walls after showers and leave the exhaust fan running. In basements, seal cracks in the foundation and make sure gutters and downspouts direct water at least 4 feet away from the house. If the area stays damp even after these steps, a dehumidifier is worth the cost — aim for indoor humidity between 30 and 50 percent.
Check the cleaned area every few weeks for the first couple of months. If you see mold returning, the moisture source was not fully stopped, and you will need to investigate further or call a contractor. Recurring mold in the same spot often signals a hidden leak inside the wall, which requires professional diagnosis.
When to hire a mold remediation contractor
Call a professional if the moldy area is larger than 10 square feet, if mold is growing on insulation or inside walls, if the drywall feels soft or has been wet for more than a few days, or if anyone in your home has respiratory problems. A mold contractor will assess how deep the mold has spread, remove and replace affected materials, and identify the moisture source. They have equipment to contain spores and dispose of contaminated materials safely.
Get at least two quotes before hiring. Ask whether the contractor is licensed in your state — requirements vary, but many states require mold remediators to hold a specific license or certification. Ask for references and verify they have liability insurance. The cost of professional remediation depends on the size and location but typically ranges from $500 to $3,000 for a small to medium job.
Frequently Asked Questions
Can I use bleach on all types of drywall?
Bleach works on standard drywall, but avoid it on mold-resistant drywall (sometimes called mold-proof or green board), as bleach can damage the special coating. Use white vinegar instead, which is safe for all drywall types.
How long does it take for mold to come back after cleaning?
If you have stopped the moisture source, mold should not return. If it does within a few weeks, the water problem was not fully fixed. If you have not identified the leak, have a contractor inspect the wall to find hidden moisture.
Is black mold on drywall more dangerous than other colors?
Black mold is not inherently more toxic than other mold colors, but all mold can trigger allergies and asthma. If you have respiratory problems or anyone in your home does, hire a professional to remove any mold rather than doing it yourself.
What should I do if mold is growing behind the drywall?
If you see mold on the surface but suspect it extends behind the wall, or if the drywall is soft or discolored in a large area, the wall likely needs to be opened and inspected. This requires a contractor or experienced handyperson to cut into the wall, assess the damage, and replace affected materials.
Do I need to replace the drywall if I caught the mold early?
If you caught it within a few days of the water exposure and the drywall is still firm and dry to the touch, cleaning the surface may be enough. If the drywall has been wet for more than a week or feels soft, replacement is safer because mold roots deep into the material and will return.