Mold on cement 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

Cement and concrete are porous, so mold roots into the surface rather than sitting on top of it. A damp cloth alone will not remove it. You need either physical scrubbing with a brush and cleaning solution, a chemical treatment that kills mold spores below the surface, or pressure washing that forces water and debris out of the pores. Which one works best depends on how much mold you have, whether the cement is indoors or outdoors, and how much time you want to spend.

The fastest method for light mold is a stiff-bristled brush and a bleach or vinegar solution. For heavy mold or mold that keeps returning, a pressure washer at 3000 PSI or higher will reach deeper into the cement. Indoors, where pressure washers create too much moisture, a commercial mold cleaner or a borax solution works better. All three approaches kill the mold you see and the spores you do not, but none will prevent mold from returning if the cement stays wet.

Key Takeaways

  • A stiff brush with bleach solution (1 part bleach to 10 parts water) removes light surface mold from cement in 30 minutes to an hour.
  • Pressure washers at 3000 PSI or higher reach mold spores deep in the pores of concrete and work best outdoors where water runoff is not a problem.
  • Vinegar and borax solutions kill mold without the fumes of bleach and are safer to use indoors or in enclosed spaces.
  • Mold returns quickly if the cement stays damp, so fixing the moisture source — poor drainage, leaks, or humidity — matters more than the cleaning method.

Cleaning with a brush and bleach solution

Mix one part household bleach with ten parts water in a bucket or spray bottle. Wear gloves and eye protection. Spray or pour the solution directly onto the moldy cement and let it sit for 10 to 15 minutes. The bleach kills the mold spores and begins to break down the mold structure.

Scrub the area hard with a stiff-bristled brush — a deck brush or grout brush works well. Push down and scrub in circles to work the solution into the pores of the cement. Rinse thoroughly with clean water and let the surface dry completely. If mold remains after one treatment, repeat the process. This method works best on light mold and on horizontal surfaces like basement floors or patios where water can drain away.

Using a pressure washer for deep mold removal

A pressure washer forces water at high speed into the pores of cement, dislodging mold spores and debris that a brush cannot reach. Rent or buy a pressure washer rated for at least 3000 PSI (pounds per square inch). Start at 3000 to 3500 PSI for most cement; go higher only if the mold is stubborn or the cement is heavily stained. Hold the nozzle 12 inches away from the surface and move it steadily across the area. Do not hold it in one spot or you risk gouging the cement.

Pressure washing works best outdoors where water runoff does not damage walls, landscaping, or neighboring property. Indoors or in enclosed spaces, the moisture created by pressure washing can spread mold spores to other areas and leave the cement too wet to dry quickly. If you must pressure wash indoors, open all windows and doors, run fans to move air out of the space, and allow several days for the cement to dry completely before closing the area up again.

Vinegar and borax solutions for indoor use

White vinegar and borax both kill mold without the strong fumes of bleach. For vinegar, spray undiluted white vinegar directly onto the moldy cement and let it sit for one hour. Scrub with a stiff brush and rinse. Vinegar is less toxic than bleach and safe to use indoors, but it works more slowly and may not kill mold as completely on the first process.

Borax is stronger than vinegar. Mix one cup of borax with one gallon of water. Spray or pour the solution onto the mold, let it sit for 10 minutes, scrub hard with a brush, and rinse thoroughly. Borax leaves a residue that continues to inhibit mold growth for a short time after cleaning, so you do not need to rinse as completely as you would with bleach. Wear gloves when handling borax solution. Both vinegar and borax are safer around children and pets than bleach, and neither produces toxic fumes in enclosed spaces.

Commercial mold cleaners and their trade-offs

Products labeled as mold cleaners or mold killers contain fungicides that are often stronger than household bleach. Brands like Wet and Forget, Mold Armor, or Zep Mold Killer are designed to penetrate porous surfaces. Read the label to confirm the product is rated for cement or concrete — some are formulated for tile or wood and will not work as well on porous surfaces.

Commercial cleaners often require less scrubbing than bleach and may work in one process on light mold. The trade-off is cost and chemical exposure. Most commercial mold cleaners cost two to three times as much as bleach or borax and contain chemicals that require ventilation and protective gear. For heavy mold or mold that returns repeatedly, a commercial cleaner may save time, but for routine cleaning, bleach or borax is usually sufficient and cheaper.

Preventing mold from returning to cement

Mold grows where moisture stays. Cement that dries quickly after rain or cleaning rarely develops mold. Improve drainage around the cement surface by sloping the ground away from foundations, clearing gutters so water does not pool, and sealing cracks where water can seep in. Indoors, use a dehumidifier in basements and crawl spaces to keep humidity below 50 percent. Fix leaks in pipes, roofs, or walls when ready.

Sealing the cement surface with a concrete sealer can slow mold growth by reducing the amount of water the cement absorbs. Sealers are not a substitute for fixing moisture problems, but they buy you time between cleanings. Reapply sealer every one to three years depending on the product and how much traffic the surface gets. Even sealed cement will eventually develop mold if it stays damp, so moisture control is always the first step.

When to call a professional

If mold covers more than 10 square feet, returns within weeks of cleaning, or is accompanied by a musty smell that spreads through the house, the moisture problem is likely larger than surface mold. A mold inspector or water damage specialist can identify whether the mold is in the cement itself, in the soil beneath it, or in the walls above it. Treating the surface will not solve the problem if water is entering from below or from a hidden leak.

Professionals have access to industrial-strength equipment and can test the mold to confirm what species it is. Some mold species are more aggressive or more likely to return. If you have health concerns — respiratory issues, allergies, or a weakened immune system — professional removal reduces your exposure to mold spores during the cleaning process. The cost is higher than doing it yourself, but it prevents the mold from spreading while you work and ensures the moisture source is identified and fixed.

Frequently Asked Questions

Is bleach or vinegar better for killing mold on cement?

Bleach kills mold faster and more completely in one process, but vinegar is safer indoors and does not produce toxic fumes. For light mold, vinegar works fine. For heavy mold or mold that keeps returning, bleach is more effective. If you have respiratory issues or pets, vinegar or borax is the safer choice even if it takes longer.

Can I paint over mold on cement instead of cleaning it?

No. Paint traps moisture against the cement and allows mold to grow underneath. The mold will continue to spread, and the paint will peel. Always clean the mold completely and let the cement dry before painting. Use a mold-resistant primer designed for concrete if the area is prone to dampness.

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

If the cement stays dry, mold may not return for months or years. If the cement stays damp or wet, mold can return in days or weeks. The speed depends on humidity, temperature, and how much moisture is present. Fixing the moisture source is the only way to prevent mold from returning quickly.

Is it safe to use bleach on cement indoors?

Bleach produces chlorine fumes that can irritate your lungs and eyes, especially in enclosed spaces. If you use bleach indoors, open all windows and doors, wear a respirator or N95 mask, and run fans to move air out of the space. Vinegar or borax are safer alternatives for indoor cement.

What PSI pressure washer do I need for mold on concrete?

Start at 3000 PSI for most mold. If the mold is stubborn or the concrete is heavily stained, you can go up to 4000 PSI. Above 4000 PSI, you risk damaging the concrete surface itself. Always test on a small, inconspicuous area first to see how the concrete responds.