Algae and moss commonly grow on exterior walls and roofs in the presence of ample moisture. Moss has a thick, grassy appearance, while algae more closely resembles a thick slime. Removing these unwanted organisms from your outer walls can prove daunting, but if you use a powerful cleaner like bleach, you can take control of the situation. Bleach contains sodium hypochlorite, a highly corrosive chemical compound that can break down even the most difficult organisms.
Mix 2/3 cup of powdered household cleaner, 1/3 cup of powdered laundry detergent, 1 quart of bleach and 1 gallon of water. You can safely apply this mixture to exterior walls, vinyl siding and roof shingles. If you want to try using bleach without other detergent, dilute it with at least four parts water. Never use undiluted bleach on walls.
Video of the Day
Insert your bleach solution into a garden sprayer or spray bottle. The spray action will allow you to spot clean any areas of algae and moss without needlessly soaking your entire wall with bleach.
Spray all algae and moss that appears on your exterior walls. Saturate the unwanted growths completely and wait 15 minutes to allow the bleach to fully penetrate and destroy the organisms.
Scrub your exterior wall with a firm scrubbing brush to further loosen and remove the organisms, eliminating any lingering stains. For this step, wear rubber gloves to protect your skin from the bleach solution.
Rinse your wall with a garden hose to remove the remaining algae and moss residue as well as the bleach solution. If you have grass or vegetation nearby, hose it down first. This water will protect it from any bleach runoff. Your exterior wall will air dry on its own.