building supply stores and hardware stores.
A Brief History of Algae-resistant AR-Shingles and What They Are Made-Of
Roofing manufacturers can provide shingles specifically made with an alternative type of mineral granule that resist algae growth. Earlier roofing manufacturers tried an algaecide coating to prevent algae growth. In the late 1980's manufacturers began using zinc granules but zinc was discontinued out of environmental concerns for using a heavy metal on roofs.
Zinc can also emit a "white rust" that builds up as a white stain or oxide. By 1996 manufacturers were using several coatings on asphalt shingles to reduce algae growth, including cuprous oxide coated granules mixed in with other granules on the shingle surface. The percentage of copper-coated granules (4% up to 10%) affects the resistance of the roof to algae.
Is algae the same as mold on roof shingles? Kirby's 1996 article confused algae and fungal growth on roofs as equivalent, which may be ok since the same chemicals that resist algae growth may also resist fungal growth and stains. We discuss removing sooty black molds on buildings below. By the way, most of the roof surface samples we have tested (pro-bono in our forensic laboratory) have been shown to be algae, not fungal and not extractive bleeding stains.
Shingle product names that include an "AR" suffix or "3M Algac Block" are products manufactured and warranted to be algae-resistant (OPINION-DF: "algae resistant" doesn't mean "algae proof", no?).
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