If your concrete driveway has turned green in spots, it is likely caused by moss, mildew, algae or mould. These spots may be localised to one area, or they may cover nearly the entire surface of the driveway. It is common for these stains to form on driveways, mainly because of their constant exposure to the elements. Regardless of how they got there, you want these unsightly spots gone. Cleaning green concrete driveways is necessary to restore the original appearance of the surface.
Remove all objects from the driveway. This will make cleaning much quicker and easier. Cover any plants or landscaping surrounding the driveway with plastic sheets that may be damaged by the cleaning solutions. Cover nearby electrical sockets with duct tape.
Scrape up as much of the green as possible using a metal scraper. Pry up moss and algae that is above the surface with the scraper. Sweep the entire driveway with a broom to remove loose dirt and debris.
Mix a solution of chlorine bleach and water into a large bucket. Use ½ gallon of bleach for every 5 gallons of water.
Dip a long-handled scrub brush into the cleaning solution. Scrub the entire driveway with the cleaning solution and scrub brush, paying special attention to the green stains.
Rinse the driveway with plain water from the garden hose set on the highest power setting. Repeat the scrubbing if the green spots are still on the driveway.
Use oxygen bleach as an alternative to chlorine bleach. It is less toxic yet effectively cleans concrete. Mix 236ml. of oxygen bleach to every gallon of hot water. Allow the oxygen bleach to dissolve completely into the water.
Pour the solution into a garden sprayer. Spray the entire driveway with a generous coating of the oxygen bleach mixture.
Allow the oxygen bleach mixture to sit on the surface for about 20 minutes. Scrub the driveway with a long-handled scrub brush.
Rinse the driveway with a garden hose set on the highest pressure setting. Scrub the driveway again with the oxygen bleach if the stains persist.
Clean with ammonia for yet another method of removing green stains from a driveway. Mix 1 cup of ammonia with every gallon of hot water. Scrub the entire driveway with the solution. Rinse with plain water.
Never mix ammonia and bleach, or products containing these two ingredients. Combining these two agents produces fumes that may be toxic and lethal. Wear rubber gloves, old clothing that covers your arms and legs, and protective eyewear to protect yourself from the cleaning agents.