Home improvement tips for cleaning green algae off the siding

Updated July 19, 2017

Your siding protects your house from the harsh elements that nature dishes out year after year. Depending on the sun and shade conditions around the sides of your house, the siding can develop algae, mould or mildew. Sometimes it is a green fungus; sometimes it is black. In either case, it is unsightly and can damage the exterior of your home. Periodically, it is necessary to remove the algae, mould or mildew and the dirt that builds up. Several methods are available to do it yourself, or you may want to consider hiring a pro. Special nozzles that shoot water long distances, long-handled brushes and sturdy ladders make the job safer and easier.

Garden Hose and Nozzle

A garden hose and nozzle, long-handled brush and cleaning solution are all you need to get your siding looking spiffy again. A bucket of warm water with some dish-washing liquid mixed in makes a good mild cleaner. First, spray a swath of siding with water 6 to 7 feet wide, starting at the top. Dip the brush into the bucket of cleaner and rub back and forth. Rinse the soap off. Avoid letting it dry on the siding. Keep rinsing from top to bottom. If the algae is particularly stubborn, you can add an oxygen bleach to the solution. Do not use chlorine bleach.

Soft Washing Technique

Soft washing uses a low-pressure water spray along with cleaners. The technique is to allow the cleaner time to do its job before rinsing off. Work in the shade as much as possible so that the solution doesn't dry on the siding before it has had time to work. Spray the area with water first. Apply cleaner from top to bottom and let soak for as much as 25 minutes. If there are densely infected spots, rub with a brush before rinsing the area with water.

Pressure Washing

High-pressure washing can be used in cleaning siding. Take care not to inject water underneath the siding accidentally, which could wet the substrate enough to encourage mould. The power washer should put out 4 gallons of water per minute and less than 1,000 PSI pressure. A machine with a chemical injector will mix the cleaning solution as it pumps the water through the washer. Follow the manufacturer's guidelines for the cleaning solution ratio. Spray the siding in 10-foot increments. Allow the cleaner to work for a few minutes, then rinse using low pressure.

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About the Author

Debra Taylor is a freelance writer whose career experience includes owning an interior design business and a retail frame shop. She also taught elementary school and middle school language arts and has a Bachelor of Arts degree in early childhood and elementary education from Lander University. She continues to be involved with children in an after school program.