Cleaning mildew from concrete is important because it can cause serious health problems if left alone. Knowing how to clean mildew from concrete can prevent falls (it can get slippery) and respiratory problems. To treat mildew, use a mildewcide — a chemical that will actually kill the fungus that causes mildew. If you don't kill it, the mildew will return.

Sunlight is another major enemy to mildew. Prune and thin trees and shrubbery that shelter concrete surfaces. Prevention is another way to control mildew. Standing water is a primary source of mildew, so mop up puddles and keep surfaces dry.

Try this mildew killer developed by the U.S. Department of Agriculture’s Forest Products Laboratory. It’s effective on all kinds of surfaces: You'll need: 1/3 cup powdered laundry detergent, 1 quart liquid chlorine bleach, 3 quarts warm water, 1 mixing bucket, safety goggles, rubber gloves, 1 stiff bristle broom or brush, 1 garden hose, and running water.


Add the bleach to the water first, then the detergent.

Even though this solution is mild, make certain to wear safety goggles, rubber gloves, and have plenty of ventilation.

Warning: Never mix bleach with ammonia! Combining the two creates a lethal gas.


Apply the solution to the affected areas.

Leave the mixture on long enough for the black or green stains to turn white, but don’t allow it to dry — 15 minutes should be long enough.


Rinse the entire area with fresh water.

To prevent the return of mildew, make sure that you have good drainage and ventilation. Proper cleaning helps fight the battle against mildew, while taking the preventative steps helps win the war!