I have black streaks of mold on the shingles on the roof of my house. How can I clean it?
By Susan from TX
I have been in the roof cleaning business for years now and I can tell you that Sodium Hypochlorite (Chlorine, bleach) is safe for roof washing. The Asphalt Roofing Manufactures Association (ARMA) recommends a solution that contains bleach to remove the black streaks. It will not harm your roof. I have videos and before & after pictures on my web site as evidence.
When looking to hire someone to wash your roof, ask them these questions:
1) Do they have the proper insurance
2) What process will they be using? (soft wash or low pressure washing is the only way to apply the proper mixture to the roof. High pressure will not only void warranties but it will damage the shingles)
3) How long will it take before the black streaks are gone? (depending on the severity of the algae infestation, it should not take more than 1 hour)
4) How long before the algae returns? (the algae needs three things to survive, moisture, shade and a food source. If you have overhanging trees or tall building nearby, it will return sooner than later. Two to four years is average with many lasting longer.)
A few of the response have the answers right ARMA is the shingle manufacturer recommendations is correct. JiminNJ is right on target with his response. Here is what it looks like up close just to get a better idea.
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