Cleaning Asphalt Shingles

Written by April Reinhardt (last updated August 1, 2022)

Today, most asphalt shingles begin with a dense mat glass fiber, shaped to the size of a shingle. The purpose of the fiberglass is to make the shingle sturdy, not waterproof. Adding a layer of asphalt to the fiberglass is what makes a shingle waterproof. Since asphalt will not adhere to fiberglass, manufacturers mix limestone fillers with the asphalt to form a bond to the fiberglass. The asphalt mixture then envelopes the fiberglass base, filling all voids and rendering the shingle utterly waterproof. The top layer of a shingle consists of ceramic granules embedded into a thin layer of adhesive asphalt.

Through weathering, the top layer of a shingle thins, leaving the organic filler vulnerable to mold and fungus growth. The most common reason for cleaning asphalt shingles is to remove fungus. Growths such as mold, fungi, and lichen feed on the limestone filler, causing shingles to break down and no longer serve as a waterproof barrier for your roof.

If your roof has tell-tale signs of fungus growth, then you need to clean your asphalt shingles. Do not wait until your entire roof becomes enveloped with thick growth. Before attempting to clean the shingles yourself, however, speak with the shingle manufacturer or the contractor who installed your roof. Different manufacturers will suggest different cleaning products and methods, and some will void your warranty if you use products or methods not approved by them. However, all roofing manufacturers agree that you should never use high pressure washers to clean your asphalt shingles since the force will strip away the ceramic granules and the top layer of asphalt, making your home vulnerable to water damage.

While most people call a contractor to clean their shingles, you can save the expense and do it yourself. Follow these steps to clean your asphalt shingles:

  1. Mix a solution of three parts water to one part bleach, and add tri-sodium phosphate as a cleaning agent. Apply the mixture to a section of your roof with a hand pump sprayer.
  2. Allow the solution to stand for fifteen minutes, and then rinse away with your garden hose. If you feel a slimy residue when you touch the shingles, then repeat the process.
  3. Make sure that you thoroughly rinse the roof since chlorine bleach can damage your shingles if you allow it to linger.
  4. If the bleach solution doesn't clean your shingles, mix a solution of one gallon of warm water with twelve ounces of dry copper sulfate,
  5. Apply the solution to your shingles using a hand pump sprayer, and wait for the mildew to turn brown.
  6. Using a push broom, sweep the mildew off of the roof.
  7. Rinse the roof thoroughly with your garden hose.

Visit your local home improvement store and discover the products available to protect asphalt singles. The 3M Corporation makes a product that prevents mold and mildew from growing on asphalt shingles. Always take extreme care when you work on your roof. The mold and mildew create slippery conditions when you add water. As a safety measure, it is best to work with another person when you clean your asphalt shingles.

Author Bio

April Reinhardt

An admin­istrator for a mutual fund man­age­ment firm, April deals with the writ­ten word daily. She loves to write and plans to author a memoir in the near future. April attend­ed More­head State Uni­ver­sity to pursue a BA degree in Ele­men­tary Edu­ca­tion. ...


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