The basic steps for removing mold from drywall and plaster

Mold on walls comes off in stages: isolate the area so spores don't spread through your home, kill the mold with a cleaning solution, scrub it away, and then dry the wall completely so it doesn't come back. For small patches (less than 10 square feet), you can do this yourself with household cleaners and basic tools. Larger areas, mold that returns quickly, or mold inside walls or behind baseboards usually means there is a moisture problem you cannot see—that is the time to call a professional.

The reason mold returns is almost always moisture. A wall that stays damp will grow mold again within weeks, even if you scrub it perfectly. Before you clean, figure out where the water is coming from: a leaking pipe, condensation from poor ventilation, a roof leak, or water seeping in from outside. If you do not fix the source, cleaning is temporary.

Key Takeaways

  • Small mold patches on walls can be cleaned with a solution of detergent and water, a commercial mold cleaner, or diluted bleach (one part bleach to ten parts water), plus a stiff brush and good ventilation.
  • Isolate the work area by closing doors and windows to prevent mold spores from spreading to other rooms while you clean.
  • Wear an N95 mask, gloves, and eye protection when scrubbing mold, because disturbing it releases spores into the air you breathe.
  • After cleaning, dry the wall completely with fans and dehumidifiers, and identify the source of moisture so the mold does not return.
  • Mold larger than 10 square feet, mold that comes back repeatedly, or mold inside walls should be inspected by a professional because it often signals a structural moisture problem.

What you need before you start

Gather your supplies before you begin. You will need an N95 mask (not a cloth mask—the N95 filters mold spores), disposable gloves, eye protection, and old clothes you do not mind getting wet. Open windows and doors to create airflow, and close doors to rooms you are not cleaning so spores stay contained.

For the cleaning solution, you have three options. A detergent solution (a few drops of dish soap in a spray bottle of water) works on fresh mold and is the gentlest on surfaces. A commercial mold cleaner (brands like Tilex or Clorox Mold and Mildew) is stronger and faster. Diluted bleach (one part household bleach to ten parts water) kills mold thoroughly but can discolor some paints and should never be mixed with ammonia or other cleaners. Choose one and stick with it—do not combine them.

You will also need a stiff-bristled brush or old toothbrush for scrubbing, clean rags or paper towels, and a dehumidifier or fan to dry the wall after cleaning. If the wall is textured or porous (like concrete or unfinished drywall), a brush is essential; if it is smooth painted drywall, a cloth and spray bottle may be enough.

Preparing the area and protecting yourself

Close all doors to the room you are cleaning. Open windows wide and position a fan to blow air out of the room, not into it. This creates negative pressure that pulls spores out instead of spreading them through your home. If you have a bathroom exhaust fan, turn it on.

Put on your N95 mask before you start spraying or scrubbing. Mold spores are invisible and become airborne when you disturb the mold—the mask keeps them out of your lungs. Wear gloves to protect your skin from the cleaning solution and from mold itself, and wear eye protection so spray does not hit your eyes.

If the mold is on drywall and you can see that the wall is soft, spongy, or crumbling, stop. That drywall is damaged and needs to be replaced, not cleaned. Call a professional to assess whether there is water damage inside the wall.

Spraying and scrubbing the mold away

Spray the moldy area generously with your chosen cleaning solution. Let it sit for 10 to 15 minutes—this gives the cleaner time to kill the mold before you scrub. Do not skip this step; scrubbing dry mold just spreads spores without killing them.

Scrub the mold with your stiff brush or cloth, using firm circular motions. Work from the edges of the moldy patch toward the center so you do not push mold spores onto clean wall. For textured walls, you may need to scrub harder and longer because mold hides in the texture. For smooth painted walls, a cloth and moderate pressure usually works.

Spray again and scrub a second time if mold remains. Some mold, especially if it has been there for weeks, needs two passes. Wipe the wall dry with a clean cloth or paper towels as you go. Do not leave the wall wet.

Drying the wall completely

After scrubbing, the wall must dry completely within 24 hours. Position a fan to blow across the wall, and open windows to let moisture escape. If the air outside is humid, run a dehumidifier in the room to pull moisture out of the air. The goal is to get the wall surface and the air around it to below 50 percent humidity.

Check the wall the next day. It should feel dry to the touch and show no wet spots. If it still feels damp, run the fan and dehumidifier for another day. A wall that stays damp will grow mold again within a week or two.

Finding and fixing the moisture source

Before you consider the job done, figure out why mold was there in the first place. Look for the obvious: water stains above the moldy spot (roof leak), condensation on the wall in winter (poor ventilation or insulation), or wet soil outside the wall (grading or gutter problem). If the wall is in a bathroom or kitchen, poor ventilation is the most common cause.

For bathroom mold, run the exhaust fan during and for 20 minutes after showers, and wipe down wet walls. For kitchen mold, use the range hood when cooking and wipe up spills. For mold on exterior walls in winter, improve insulation or add a dehumidifier to the room. For mold near the foundation, check that gutters are clean and downspouts drain at least 4 feet away from the house.

If you cannot find the source—if the wall is damp but you see no leak, no condensation, and no obvious water entry—that is a sign of a hidden problem like a pipe leak inside the wall or water seeping through the foundation. That calls for a professional inspection before you clean, because cleaning alone will not stop the mold from coming back.

When to call a professional instead

Do not attempt to clean mold yourself if the patch is larger than 10 square feet, if mold returns within a few months of cleaning, if the wall feels soft or crumbles when you touch it, or if you suspect mold is inside the wall (you see it around a pipe or behind a baseboard but cannot see how far it extends). These situations usually mean there is active moisture damage that needs professional assessment and repair.

A mold remediation professional has equipment to detect moisture inside walls, can remove and replace damaged drywall, and can identify the source of water entry. They also follow containment protocols to prevent spores from spreading during removal. The cost varies widely depending on the size and location of the mold, but it is worth it if the alternative is mold that keeps coming back or spreads to framing and insulation.

Frequently Asked Questions

Can I use bleach on all wall surfaces?

Bleach works on tile, concrete, and some painted drywall, but it can discolor or damage some paints, wallpaper, and natural stone. Test it on a hidden spot first. Never mix bleach with ammonia or other cleaners—the fumes are toxic. For delicate surfaces, use a detergent solution or commercial mold cleaner instead.

What if mold comes back after I clean it?

Mold returns when moisture returns. If it comes back in the same spot within a few weeks, there is still a water source you have not found or fixed. Check for leaks, condensation, or poor drainage again. If you cannot find it, have a professional inspect for hidden moisture inside the wall or foundation.

Is it safe to paint over mold?

No. Paint traps moisture and lets mold grow underneath. Always clean and dry the wall completely, fix the moisture source, and wait at least 24 hours before painting. If mold returns under new paint, the underlying problem is still there.

Do I need to wear a mask if the mold patch is small?

Yes. Even small patches release spores when you spray and scrub them. An N95 mask is inexpensive and protects your lungs. Cloth masks and surgical masks do not filter mold spores effectively.

How do I know if mold is inside the wall?

You cannot see inside a wall, but signs include mold that appears around pipes, baseboards, or corners; a musty smell that does not go away after cleaning; or soft, discolored drywall. If you suspect mold inside the wall, do not cut into it yourself—call a professional to assess the damage before you disturb it.