Shielding Aging Shingles From Acidic Lichen, Algae and Heat https://www.ganjingworld.com/article/1itp11j2hje2fNU7Wsgc17cLm1n31c/shielding-aging-shingles-from-acidic-lichen-algae-and-heat When you pull into the driveway and see weird spots on your roof, it’s never a good feeling.