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Old 06-20-2012, 02:55 PM   #16
Slingah
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Join Date: May 2003
Location: Marshfield, MA
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One or more sections of the roof covering appear stained. An algae known as Gloeocapsa Magma is the most likely culprit and this algae affects nearly 80 percent of the homes across the United States. Gloeocapsa Magma is a species of algae that causes black streaking and discoloration on asphalt/fiberglass shingles. The black staining you see on many roofs is caused by the life cycle of algae and fungus spores that land on houses via wind or wildlife. While this algae can grow just about anywhere, it prefers humid environments. A preferred food source of this algae is limestone which is used as "filler material" by most shingle manufactures. Higher quality shingles are manufactured with preventative measures such as copper or zinc containing granules. Several methods exist to prevent and clean infected areas. Installing zinc or copper strips near the roof ridge can prevent further algae growth.

Take a photo Paul and post it. Forget that stuff you used. Trust me the only way to rid of it is strong bleach and a surfactant.
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