Concrete mold comes off with a stiff brush, bleach solution, and elbow grease—but the real work is keeping it from coming back

Mold on concrete is usually surface growth that hasn't penetrated deep into the material. You can remove it yourself with a wire brush, household bleach diluted in water, and a spray bottle. The process takes a few hours and costs under $20 in supplies. What matters more than the removal itself is understanding why it grew there—usually moisture, poor drainage, or shade—because concrete that stays wet will grow mold again within weeks.

This guide covers how to clean mold off concrete safely, what tools actually work, and the drainage fixes that stop it from returning. If the mold covers more than 10 square feet, or if you have respiratory problems, consider calling a professional mold remediation company instead.

Key Takeaways

  • Mix one part household bleach with three parts water in a spray bottle, spray the moldy area, wait 10 to 15 minutes, then scrub with a stiff-bristled brush.
  • Wear gloves, eye protection, and a dust mask when scrubbing, because mold spores become airborne and bleach fumes are irritating.
  • Concrete mold returns quickly if the surface stays damp, so the real fix is improving drainage or removing shade that traps moisture.
  • Pressure washing alone does not kill mold—it spreads spores and leaves roots behind—so always use a chemical treatment first.
  • If mold covers more than 10 square feet or you have asthma or a weakened immune system, hire a professional instead of doing it yourself.

What you need to clean mold off concrete

Gather these items before you start: household bleach (the regular 5 percent sodium hypochlorite kind), a spray bottle, a stiff-bristled brush (a wire deck brush works well), a bucket, water, rubber gloves, safety glasses, and a dust mask rated N95 or better. You may also want old clothes you don't mind staining, because bleach discolors fabric.

Do not use vinegar or baking soda on concrete mold. Both are popular for mold on drywall or tile, but concrete is porous and alkaline—vinegar is too weak to penetrate, and baking soda does not kill mold spores. Bleach works because it chemically breaks down the mold structure. If you prefer not to use bleach, a commercial mold killer labeled for concrete (like Wet & Forget or Concrobium) will work, though it costs more and takes longer to show results.

The step-by-step process for removing mold

Start by mixing one part bleach with three parts water in your spray bottle. Do this outdoors or in a well-ventilated space—bleach fumes are strong. Put on your gloves, glasses, and mask before you begin.

Spray the moldy concrete thoroughly until it is wet but not dripping. Let it sit for 10 to 15 minutes. This contact time is when the bleach kills the mold. Do not skip this step or scrub when ready—the bleach needs time to work.

After 15 minutes, scrub the area hard with your stiff brush, using circular motions. Push down firmly. You are trying to break up the mold layer and work the bleach into the pores of the concrete. Scrub for two to three minutes per square foot. Rinse thoroughly with clean water from a hose. Let it dry completely—ideally in sunlight, which also kills mold spores.

If mold remains after one treatment, repeat the process. Stubborn mold sometimes needs two applications. Do not increase the bleach concentration—it will not work faster and creates toxic fumes if mixed with other cleaners.

Why pressure washing alone does not work

Pressure washing removes surface dirt and can make mold less visible, but it does not kill the mold. The spores and root structure survive, and the high-pressure water actually spreads spores across the concrete and into the air. Pressure washing after chemical treatment is fine—it rinses away dead mold and debris—but it should never be your first step.

If you rent a pressure washer, use it only after the bleach has done its job and the mold is dead. Set the pressure to 1500 PSI or lower on concrete, because higher pressures can damage the surface or force water into cracks where it causes freeze-thaw damage in winter.

Fixing drainage so mold does not return

Concrete mold almost always means water is sitting on or near the surface. Identify where water pools after rain. If water collects in low spots on a patio or driveway, the concrete may need to be re-sloped—a job for a concrete contractor. If water is coming from a gutter or downspout, redirect it away from the concrete. Gutters should drain at least 4 to 6 feet from the foundation or patio edge.

If the moldy area is in shade—under a tree, on the north side of a building, or under an overhang—mold will return even if you clean it, because shade prevents the concrete from drying. Trim tree branches to let more sunlight reach the surface, or accept that you will need to clean it again in a year or two. Some homeowners in very shady spots treat the concrete with a mold-inhibiting sealer after cleaning, which slows regrowth but does not stop it permanently.

Check for cracks in the concrete. Water seeps into cracks and stays trapped, creating an ideal environment for mold. Small cracks can be sealed with concrete crack filler from a hardware store. Larger cracks may need professional repair.

Safety precautions when working with bleach

Never mix bleach with ammonia, vinegar, or other cleaners. This creates toxic chlorine gas, which can cause serious lung damage or death. If you have used another cleaner on the concrete, rinse it thoroughly and let it dry before explore bleach.

Wear rubber gloves to protect your skin. Bleach is caustic and will irritate or burn skin with prolonged contact. Wear safety glasses because bleach splashes can damage your eyes. Wear an N95 mask to avoid inhaling mold spores and bleach fumes. Work outdoors or open all windows and doors for ventilation.

If you have asthma, emphysema, or a weakened immune system, do not do this work yourself. Mold exposure can trigger serious respiratory problems. Hire a professional mold remediation company instead. The cost is usually $300 to $800 for a small area, depending on your region and the extent of the mold.

When to call a professional mold remover

Call a professional if the mold covers more than 10 square feet, if it has penetrated deep into the concrete (visible as dark staining that does not come off with scrubbing), or if you have health conditions that make mold exposure risky. Professionals have commercial-grade equipment, better ventilation control, and can assess whether the mold indicates a larger moisture problem in your foundation or basement.

A professional will also test the concrete to confirm it is mold and not efflorescence—a white or gray mineral deposit that looks similar but requires different treatment. If you are unsure what you are looking at, take a photo and email it to a local mold remediation company for a free assessment before you spend time cleaning.

Frequently Asked Questions

Can I use a bleach pen or spray instead of mixing my own solution?

Bleach pens are too thick and concentrated for concrete—they do not spread evenly and waste product. Spray bottles of pre-mixed bleach work but cost more per ounce. Mixing your own is faster and cheaper. A gallon of household bleach costs about $3 and makes enough solution to treat 200 to 300 square feet.

Will the mold come back after I clean it?

Yes, if the concrete stays damp or shaded. Mold spores are everywhere in the air and soil. They land on concrete and grow whenever conditions are wet and dark. Cleaning kills what is there now, but fixing drainage and improving sunlight prevents it from returning quickly. In very shady or wet areas, mold may return within a year.

Is it safe to use bleach on concrete near plants or a garden?

Bleach will kill plants it contacts directly, so be careful not to spray nearby soil or grass. Rinse the area well after scrubbing. Diluted bleach that drains away from plants is generally safe once it dries, but concentrated bleach or repeated applications can damage soil. If the moldy concrete is right next to a garden bed, consider using a commercial mold killer labeled safe for landscaping instead.

What if the mold is inside my basement or crawlspace?

The same cleaning method works, but basement mold usually signals a moisture problem—either water seeping through the walls, condensation from poor ventilation, or a high water table. Clean the visible mold, but also address the moisture source, or it will return. This often requires a dehumidifier, better ventilation, or professional waterproofing. If mold covers a large basement floor, hire a professional.

Can I seal concrete after cleaning to prevent mold?

Concrete sealers slow mold growth but do not stop it. A penetrating sealer (like siloxane) is more effective than a film-forming sealer (like acrylic) because it lets the concrete breathe. Sealing is worth doing if the area is shaded and you want to extend the time between cleanings, but it is not a substitute for fixing drainage or improving sunlight.