Removing Moss, Mildew, Fungus and Associated Stains on Roofs
Roof cleaning is a topic that draws yawns in New England but causes shudders and screams of agony from Florida and points south, where vegetable life seeks world domination! How do we keep that "fungus among us" under control. (Graphic left courtesy Spray and Forget mildew and moss remover.)
Since starting on a quest for the ideal method of cleaning fungus and algae from roofs, I have contacted dozens of individuals and companies. Some of my readers came forward with suggestions and a few companies also supplied information helpful to this research.
For the purposes of this article, the terms "mildew", "fungus", "algae" and "moss" are interchangeable... even though their mothers' might object!
Chlorine bleach cleaning mixtures are one option...
If you've had experience with mold and mildew in the home, you know the best mildew remover is chlorine bleach. But outdoor, heavy duty cleaning usually calls for more heavy-duty mixtures such as TSP and chlorine bleach (see the TSP page for more details), or specialty additives such as Jomax from Rustoleum, which combines a cleaner with a bleach activator.
How to use bleach mixtures on your roof...
The following procedure is for bleach-cleaning only using JOMAX. (Other cleaning options are mentioned later in this article.) If JOMAX is not available in your area, use a TSP mixture with bleach added.
If you think it wise to leave the bleach-brew on the roof longer than the recommended time, think again! As mentioned earlier, long term exposure to bleach can damage most any surface, and your roof is no exception. However, this piecemeal approach is the likely to cause the least damage.
Problems with using bleach on asphalt roofs...
There is some concern regarding the use of chlorine-based products on asphalt roofs. Household bleach can damage asphalt due to its high sodium content. Apparently, the sodium causes an electrochemical reaction that reduces the elasticity of the asphalt leading to stiffness, brittleness and curling of the shingles. (I suffer from two of those symptoms myself!)
Thankfully, there are some "killer" alternatives to bleach...
1) Sodium hydroxide products are NOT recommended!! A chemical alternative to bleach uses the antifungal agent sodium hydroxide... also known as lye. Lye-based products appeared on the market a few years ago, but turned out to be even more dangerous to use than bleach! Even at low concentrations, permanent damage could be done to the roofing, possibly even dissolving the roofing nails!
Fortunately, most lye-based products have been removed from the market.
2) Here are a few bleach-free chemical treatments that can help keep fungus under control:
Preventing reinfestation... zinc strips are one option
If you wish to prevent reoccurrence of fungus, there are a few options. Zinc strips (left) have been used for many years as an algae preventative. StainHandler.com offers sets of 3' zinc strips, which are attached near the peak of the roof. When it rains, a slight amount of zinc dissolves from the strips and coats the roof, inhibiting algae and fungus growth.
Anti-Growth from GSI/Camden Products offers long-term protection against the return of mildew once the cleaning is done. Unlike the other products mentioned on this page, Anti-Growth can be used for interior applications.
Would you believe... fungus-resistant shingles??
Yessiree... the 3M Company has developed an additive for asphalt roofing shingles using copper granules. This unique advance in shingle technology gives long-term fungus protection for the entire roof. They call it the AlgaeBlock system. You can find more information on these special roofing shingles HERE.
3M is not a manufacturer of asphalt shingles, just the granules. However, at the time of this writing they do list a number of companies that are producing shingles meeting their specifications.