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Asphalt Roofing Manufacturers Association

Tel: (202) 207-0917 • Fax: (202) 223-9741

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Algae Discoloration of Roofs


Algae discolorations are difficult to remove from roofing surfaces, but may be lightened by applying a solution of

chlorine bleach, trisodium phosphate, and water. Solutions for these ingredients may vary between shingle manufacturers and depend on the amount of discoloration. Solutions range from one cup TSP, one gallon bleach and five gallons of water, to one cup TSP and 2.5 gallons each of bleach and water.

First, gently disperse this solution on the roofing surface. Use normal precautions for handling bleach. Be sure to apply it carefully to avoid damage to other parts of the building and its surrounding landscape. Avoid scrubbing the surface, as this friction may loosen and remove granules. If possible, always work from a latter and/or walkboards to avoid direct contact with the roof surface. Observe all possible safety precautions when working on or near the roof.

Finally, rinse the solution from the roof by gently spraying the surface with water.
Be warned that this solution application and rinse process will make the roof surface slippery and potentially hazardous to walk on during treatment.