Removing Black Stains From Asphalt Roofs
Your asphalt roof protects the interior of your home from snow and rain, and all of the weather conditions in between. However, the constant weather exposure that your roof experiences can exact a toll on the material; over time, you may begin to see black or dark green stains and streaks establish themselves. These streaks and stains are caused by moss and algae growth on your asphalt shingles themselves and can lead to structural damage if allowed to sit for an extended period of time. Fortunately, they can be easily removed with the right tools and a little bit of elbow grease.
Before You Begin
Gather all of the materials that you'll be using before you get started so that the cleaning process goes as smoothly and quickly as possible. You'll need a garden hose, safety glasses, rubber gloves, a ladder, a pump sprayer, tarps, and bleach. For extremely bad cases, you may also want to use trisodium phosphate. All of these items can be found at most hardware and grocery stores if you do not already own them.
Cleaning Algae Stains From Asphalt
First things first, you'll want to use tarps to cover up any plants which may be around the edge of your home or in an area where they are likely to be exposed to your cleaning solution.
Next, mix one part of bleach into four parts water in your pump sprayer. This will crease a cleaning mixture that will kill the algae, but isn't powerful enough to cause damage to your asphalt shingles.
Then, with your safety gloves and glasses on, you can spray your roof down. While you should pay particular attention to the stained areas, it's a good idea to cover the entirety of your roof, as algae and mold spores that have not yet bloomed and thus are not visible may be present elsewhere.
Let the cleaning solution sit on your shingles for anywhere between fifteen and thirty minutes to do its job, and then use your garden hose to spray down your roof. Be as thorough as possible; you don't want to leave the bleach on your shingles, as it can cause degradation over time.
If the stains still remain, you can mix half a cup of trisodium phosphate into a gallon of water, and then apply it in much the same manner. This will provide a much deeper clean than bleach will, but is much more toxic to nearby plants and can cause significantly more damage to your shingles if allowed to sit for too long, so be sure to rinse your roof thoroughly fifteen minutes after application.
Contact roofing companies in your area if you would prefer to have professional assistance.