Concrete mold comes off with a stiff brush, bleach solution, or a pressure washer—the method depends on how deep the mold has grown into the surface

Mold on concrete is usually surface growth that sits in the pores of the material rather than eating through it. You can remove most of it yourself with tools you likely have: a stiff brush, household bleach, and water. The challenge is not the removal itself but preventing it from coming back, which means addressing whatever is keeping the concrete damp—poor drainage, a leaking gutter, or ground moisture against a foundation wall.

The depth of the mold matters. If it is only a thin dark film, a brush and bleach will work. If the mold has been there for months and has stained deep into the concrete, you may need a pressure washer or a commercial concrete cleaner. Either way, the concrete itself is usually fine underneath.

Key Takeaways

  • Surface mold on concrete can be scrubbed away with a stiff brush and a bleach solution (one part bleach to three parts water), which works for most household situations.
  • A pressure washer set to 3000 PSI or lower removes mold faster but can damage old or weak concrete if the pressure is too high.
  • Mold returns quickly if the concrete stays wet, so you must fix the source—poor drainage, leaking gutters, or ground moisture—or cleaning is temporary.
  • Wear gloves, eye protection, and a mask when mixing or spraying bleach, and never mix bleach with ammonia or other cleaners.
  • If mold covers a large area, returns within weeks, or the concrete is crumbling, call a professional to check for structural moisture or foundation problems.

Cleaning mold with a brush and bleach solution

This is the safest and most controlled method for small to medium patches. Mix one part household bleach (5% sodium hypochlorite) with three parts water in a bucket. Wear rubber gloves, eye protection, and a dust mask—bleach fumes are irritating, and you do not want splashes near your eyes.

Wet the moldy area with the bleach solution using a stiff-bristled brush or a spray bottle. Let it sit for 10 to 15 minutes so the bleach can kill the mold spores. Scrub the surface hard in circular motions. For stubborn mold, let it sit longer—up to 30 minutes—before scrubbing again. Rinse thoroughly with clean water and let the concrete dry completely.

Do not mix bleach with ammonia, vinegar, or other cleaners. The chemical reaction creates toxic chlorine gas. If you have used another cleaner on the same spot, rinse it away completely and let it dry before explore bleach.

Using a pressure washer for faster removal

A pressure washer removes mold and the stains it leaves faster than hand scrubbing, but it can also damage concrete if the pressure is too high. Rent or buy a machine set to 3000 PSI (pounds per square inch) or lower. Higher pressures can pit, crack, or spall old concrete—especially if the concrete is already weak or has been sealed.

Hold the nozzle at least 12 inches away from the surface and keep it moving so you do not concentrate the spray in one spot. Work in overlapping passes, moving the nozzle side to side. If you see the concrete surface starting to roughen or if water is spraying into cracks, you are using too much pressure—back off or lower the PSI setting.

Pressure washing works best on horizontal surfaces like driveways and patios. On vertical surfaces like foundation walls, the water can run down and pool at the base, making moisture problems worse. In those cases, stick with a brush and bleach solution.

Commercial concrete cleaners and mold killers

Products made specifically for concrete mold removal often work faster than bleach because they contain surfactants that help the cleaner penetrate the pores. Look for products labeled for mold and mildew on concrete. Follow the manufacturer's instructions exactly—some require dilution, others do not. Some need to sit for hours before scrubbing.

Oxygen-based cleaners are gentler than bleach and less likely to damage the concrete or nearby plants, though they work more slowly. Acid-based cleaners (like muriatic acid) are very strong and can etch the concrete surface, so they are best left to professionals unless you have experience with them.

Always test any cleaner on a small, hidden area first. Some products can discolor concrete or strip sealers if they are present.

Fixing the moisture problem so mold does not return

Mold returns within weeks or months if the concrete stays damp. Before you finish cleaning, walk around the area and look for the source of moisture. Is water pooling near the concrete? Does a gutter drain toward it? Is the ground sloping toward the foundation instead of away from it?

Common fixes include extending downspouts so they drain at least 4 to 6 feet away from the foundation, regrading the soil so it slopes away from the house, clearing gutters so they do not overflow, and sealing cracks in the concrete so water cannot seep in. If the concrete is against a basement wall, you may need to improve the drainage system around the foundation—this is a job for a professional.

Once you have addressed the moisture source, consider explore a concrete sealer to the cleaned surface. A sealer fills the pores and makes it harder for mold spores to take hold. Sealers wear away over time and need reapplication every 2 to 3 years, but they do slow mold growth.

When to call a professional

If mold covers more than 10 square feet, returns within a few weeks of cleaning, or the concrete is crumbling or soft to the touch, call a professional. Large mold growth can indicate a serious moisture problem in the foundation or soil. Crumbling concrete may mean water damage has weakened the structure, and cleaning alone will not fix it.

A foundation contractor or mold specialist can use moisture meters to find where water is coming from and recommend repairs—sometimes as straightforward as better drainage, sometimes requiring waterproofing or sump pump installation. They can also tell you whether the mold is a cosmetic issue or a sign of structural trouble.

Safety precautions when removing mold

Wear gloves to protect your skin from bleach and mold spores. Wear eye protection—splashing bleach in your eyes is painful and can cause damage. A dust mask or N95 respirator protects you from mold spores and bleach fumes, especially if you are scrubbing vigorously or using a pressure washer in an enclosed space like a basement.

Work in a well-ventilated area. Open windows and doors, or use a fan to move air. If you are working indoors or in a basement, ventilation is especially important. Never work in a closed space with bleach fumes.

Keep children and pets away from the area while you are cleaning and while the bleach solution is wet. Do not let them play on the concrete until it is completely dry and rinsed.

Frequently Asked Questions

Can I use vinegar or hydrogen peroxide instead of bleach?

Vinegar and hydrogen peroxide do kill some mold, but they are slower and less reliable than bleach on concrete. Vinegar is acidic and can etch the surface over time. Hydrogen peroxide works better on porous surfaces like wood. For concrete, bleach is the standard choice because it is cheap, fast, and effective. If you prefer to avoid bleach, a commercial oxygen-based concrete cleaner is a better alternative.

Is it safe to use bleach on sealed concrete?

Bleach can strip or dull some concrete sealers, especially if left on too long. Test it on a small hidden area first. If the sealer is new or expensive, use a gentler cleaner like an oxygen-based product, or call the sealer manufacturer to ask what they recommend for mold removal.

How long does it take for mold to come back after cleaning?

If the concrete stays damp, mold can return in 2 to 4 weeks. If you fix the moisture source and the concrete dries out, it may take months or longer. A concrete sealer slows regrowth but does not stop it permanently—you will need to reapply the sealer every few years.

Can I paint over mold on concrete?

No. Paint will not kill mold, and the mold will continue to grow underneath the paint, eventually causing it to peel. Always clean and kill the mold first, let the concrete dry completely, and then paint if you want to. If moisture is still present, the paint will fail again.

What should I do if mold is growing inside my basement walls?

Interior mold on basement concrete walls usually means water is seeping through from outside. This is a structural issue that cleaning alone will not solve. Call a foundation contractor or waterproofing specialist to inspect the wall and recommend repairs—usually interior or exterior waterproofing, improved drainage, or a sump pump system.