Green algae will begin to grow on cement or concrete when the surface stays constantly damp. Many homes in humid climates are constantly battling algae and fungus growth. Even though algae itself does not damage the structural stability of the cement or concrete, it can still cause troublesome problems. If left untreated, the algae will permanently discolor the cement or concrete. In addition, algae growth is rather slippery and will become a safety hazard when it is allowed to grow on walkways.
Rinse the surface algae off the cement or concrete with a water hose.
Put on rubber gloves. Pour white vinegar directly on the surface and scrub it with a scrub brush. Use a vigorous back-and-forth motion. Rinse the vinegar off with the water hose.
Mix 1 cup of bleach and 1 gallon of water together in a bucket. Use a scrub brush to scrub the mixture into any lingering algae stains. Wait for 10 to 15 minutes before continuing.
Rinse the cement or concrete clean with the water hose. Continue with the remaining steps if any algae remain.
Saturate difficult-to-remove algae with an antifungal cleaner. Each brand has its own set of instructions, so follow the directions on the product label.
Scrub the antifungal cleaner with a scrub brush and rinse the cement or concrete with a water hose.