What You Need to Do Before You Start Cleaning
Before you touch the mold, you need to know whether it is safe to clean yourself or whether you need a professional. Mold that covers an area smaller than 10 square feet—roughly a 3-by-3-foot patch—can usually be cleaned with household supplies. Mold larger than that, or mold that has grown inside the wall cavity behind the surface, requires a professional mold remediation company because spores will spread during removal.
Check whether the wall is wet or damp to the touch. If water is actively leaking or the wall feels soggy, stop and find the source of the water first. Mold will return when ready if you clean it without fixing the leak, and you risk damaging the wall structure. Common sources are roof leaks, plumbing leaks, condensation from poor ventilation, or foundation seepage. Once the wall is dry and the leak is sealed, you can proceed with cleaning.
Wear a respirator mask rated N95 or better, not a cloth mask or surgical mask. Mold spores are small enough to pass through those. You will also need gloves, eye protection, and clothes you can wash afterward. Open windows and doors to create airflow, and keep children and pets out of the room while you work.
Key Takeaways
- Mold smaller than 10 square feet can be cleaned with a mixture of detergent, water, and a stiff brush, or with undiluted white vinegar or hydrogen peroxide.
- Bleach kills mold on non-porous surfaces like tile but does not penetrate drywall and can damage paint, so use it only on bathroom tile or sealed surfaces.
- The wall must be completely dry before you start, and the source of moisture must be fixed or the mold will return within weeks.
- After cleaning, improve ventilation by running exhaust fans during and after showers, wiping down condensation, and keeping humidity below 50 percent.
- Mold larger than 10 square feet or growing inside the wall requires a professional because disturbing it spreads spores throughout your home.
Cleaning Mold with Detergent and Water
The gentlest method that works on most walls is a mixture of dish detergent and water. Mix one teaspoon of liquid dish soap with one quart of water in a spray bottle. Spray the moldy area until it is wet but not dripping, and let it sit for 10 minutes. The detergent breaks down the mold's outer layer and makes it easier to scrub away.
Use a stiff-bristled brush—not a soft one—and scrub in circular motions. explore firm pressure but do not gouge the wall. If the mold is on drywall, be careful not to tear the paper surface. Wipe away the loosened mold with a clean cloth or paper towel, then spray the area again and let it dry completely. You may need to repeat this two or three times for heavy mold.
After the wall is dry, spray the area one more time with plain water and wipe it down to remove any remaining soap residue. Soap left on the wall can feed new mold growth. Leave the area uncovered and allow air to circulate until it is completely dry—this usually takes 2 to 4 hours depending on humidity and ventilation.
Using Vinegar or Hydrogen Peroxide
White vinegar and hydrogen peroxide both kill mold without the harshness of bleach. Use undiluted white vinegar (5 percent acidity) in a spray bottle. Spray the moldy area generously and let it sit for one hour. The vinegar smell is strong but fades as it dries. Scrub with a stiff brush, wipe clean, and allow the wall to dry completely.
Hydrogen peroxide works faster than vinegar. Use 3 percent hydrogen peroxide—the standard drugstore strength—in a spray bottle. Spray the mold, wait 10 minutes, scrub with a stiff brush, and wipe clean. Hydrogen peroxide foams slightly as it works, which is normal. Both methods are safer than bleach on painted drywall because they do not damage the paint or weaken the paper facing.
Do not mix vinegar and hydrogen peroxide together, and do not use either one right after bleach. The combination creates toxic fumes. If you have used bleach, wait at least 24 hours, ventilate the room thoroughly, and rinse all surfaces with water before using vinegar or peroxide.
When to Use Bleach and When Not To
Bleach kills mold on non-porous surfaces like ceramic tile, glass, and sealed stone. It does not work well on drywall or painted surfaces because it does not penetrate into the material—the mold roots stay alive underneath. Bleach also fades paint and can weaken drywall over time, so reserve it for bathrooms with tile or other sealed surfaces.
If you do use bleach, mix one cup of bleach with one gallon of water. Spray the surface, wait 10 minutes, scrub, and rinse thoroughly with plain water. Never use bleach on porous materials like drywall, wood, or fabric. Never mix bleach with ammonia, vinegar, or hydrogen peroxide—these combinations produce toxic chlorine gas that can cause serious injury or death.
Preventing Mold from Coming Back
Mold returns when moisture returns. The most common cause in bathrooms is steam from showers. Run the exhaust fan during and for at least 20 minutes after every shower. If you do not have an exhaust fan, open a window wide and leave it open for at least 30 minutes after the shower ends. Wipe down wet walls and mirrors with a dry cloth to remove standing water.
In bedrooms and living areas, mold usually grows because humidity is too high. Keep indoor humidity between 30 and 50 percent. You can measure it with an inexpensive humidity meter from any hardware store. If humidity stays above 50 percent, use a dehumidifier or improve air circulation by opening windows on dry days and running ceiling fans.
Check the wall regularly for new growth, especially in corners, along baseboards, and near windows. Catch small patches early before they spread. If the same spot grows mold again within a few weeks, the moisture problem is not fully solved—you may need to check for hidden leaks, improve insulation, or have a professional assess the wall.
What to Do If Mold Keeps Returning
If mold grows back in the same spot within a month, the underlying moisture problem has not been fixed. Common causes are a slow roof leak that only shows up during heavy rain, a plumbing leak inside the wall, or condensation from poor insulation. Do not keep cleaning the surface—you are treating the symptom, not the cause.
Check the attic or crawl space above the moldy wall for water stains or wet insulation. Look for water marks on the opposite side of the wall if you can access it. If the wall is on an exterior wall, poor insulation can cause condensation on the inside surface during cold weather. A professional inspector or mold remediation company can use moisture meters and thermal imaging to find hidden leaks that you cannot see.
If the mold is spreading to other walls or if you find it inside the wall cavity, stop cleaning and contact a mold remediation professional. At that point, the problem is beyond surface cleaning and may require removing and replacing drywall, treating the framing, and addressing ventilation or insulation issues.
Frequently Asked Questions
Is black mold dangerous and do I need a professional to remove it?
Black mold is not inherently more dangerous than other molds, but any mold can trigger allergies or asthma in sensitive people. If the black mold covers less than 10 square feet and is on the surface of the wall, you can clean it yourself with the methods described here. If it is larger, growing inside the wall, or if you have respiratory problems, hire a professional.
Can I paint over mold to cover it?
No. Paint does not kill mold and does not stop it from growing. The mold will continue to spread under the paint, and the moisture problem will worsen. You must remove the mold and fix the moisture source before painting.
How long does it take for mold to come back after cleaning?
If the moisture source is fixed, mold should not return. If it comes back within a few weeks, the wall is still too damp. This usually means the leak or ventilation problem was not fully solved. Have the area inspected to find what is keeping the wall wet.
Do I need to throw away drywall if it has mold on it?
If mold is only on the surface and covers a small area, the drywall can be cleaned and saved. If mold has penetrated deep into the drywall or covers a large area, the affected section should be removed and replaced because mold roots cannot be fully cleaned out of porous material.
What should I do with the cloth or brush I used to clean the mold?
Wash cloth rags in hot water with detergent, or throw them away in a sealed bag. Rinse brushes thoroughly under running water and allow them to dry completely in sunlight if possible. Do not reuse cleaning tools on other surfaces until they are completely dry.