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You can use a mold-killing detergent, diluted bleach, or a commercial cleaner made specifically for killing mold. Don't mix anything other than water with bleach, as certain cleaning agents can produce highly toxic fumes when mixed with bleach. For a diluted bleach solution, mix three parts water with one part bleach in a bucket. Don't forget to test a small, discreet area first. Bleach and other chemicals can discolor concrete that's been colored or stained. Any organic material adjacent to the moldy area can be infected. Throw away any disposables like cardboard boxes. Set aside other removable items like furniture or area rugs. Use a heavy duty sponge or scrub brush to apply your chosen cleaning solution to all visible moldy areas on the concrete. Scrub the areas vigorously. If you're using mold-killing detergent, apply it directly to the spots and scrub it with a bristle brush. Don't use a wire brush, which can scratch concrete. Wear old clothes, rubber gloves, safety goggles and a respirator or dust mask. If the spots aren't lifting, leave the solution to sit for several minutes. Then scrub the areas with the solution until the mold is gone. Use a hot water pressure washer for the fastest and most effective rinse. Wear safety goggles, sturdy footwear and long pants. Use a pressure rating of at least 3000 psi with a flow rate of at least four gpm (gallons per minute). This should lift any organic matter that has seeped into the pores of the concrete. If you don't want to use a pressure washer, try a regular water hose. You can rent a pressure washer at a home or building supply store. You may need a van, pickup truck or SUV to transport it, and a friend to help load and unload it. Ask the rental agent how to use the washer and to give you any safety precautions. Find out if the washer comes with nozzles. Don't use settings finer than fifteen degrees. Never use a zero degree nozzle on a pressure washer. Once it's dry, inspect carefully for any mold that may not have been cleaned. If there is still visible mold, rinse the area clean and try one of the stronger methods you haven't used yet: diluted bleach or commercial cleaner. Leather, wood or inorganic furniture can be deep cleaned. Upholstered furniture with visible mold will need to be disposed of or reupholstered by a professional. Carpet that shows significant mold growth or is soaked completely through will need to be removed.
Choose a cleaning agent to treat the mold. Remove affected items. Apply the solution. Let the solution soak. Rinse outdoor concrete. Dry interior concrete with a towel. Clean items you've set aside before placing them back in the area.