Black Algae Stains On Asphalt Shingles
Summary: Roof algae stains occur on asphalt shingle roofs, usually on the north side. The roof algae starts as dots, then takes a cone shape and can eventually cover your entire roof! Introduce copper or zinc strips to kill roof algae. You can also use Oxygen Bleach.
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Black-Streaked Shingles, Algae Resistant Shingles Manufacturer
DEAR TIM: I've got a problem. Three years ago, I had a new fiberglass asphalt shingle roof installed. It was the same color as my old roof, a light tan. Within the past 6 months, several areas of the roof have developed a dark, mildew-like stain. It is spreading. The climate hasn't changed and there are no trees that shade my roof. What in the devil is going on? Can I easily remove the staining? Can it be prevented? Ginny U., Ft. Pierce, FL
DEAR GINNY: They're heeeeeere! You, my friend, have been invaded by Gloeocapsa magma, a very hardy algae. These dudes have probably been up on your new roof since day one. The streaks and discoloration you are now seeing is an accumulation of their dead, dark colored cells. While this algae can grow just about anywhere in the continental USA, it really likes humid environments. The algae was deposited on your roof by wind and/or wildlife.
This algae most probably invaded your last roof as well. But, it starved to death. The new fiberglass shingles you just installed are actually quite different from your old shingles. Your new shingles contain lots of ground up limestone. It is used as a filler to increase the weight of the shingles.
Guess what? Gloeocapsa magma loves to eat limestone. Older shingles used an asphalt saturated felt paper made from scrap cotton rags and wood chips. New synthetic textiles eliminated the cotton rag market, so roofing companies switched to fiberglass. They solved one problem but created another.
Consider installing long, seven inch wide strips of copper underneath the last full course of shingles at the top of your roof. You should be able to slide the copper up under the shingles approximately five inches or so. This will leave approximately two inches exposed to the weather.
If you are getting ready to install new shingles, you need not do this. Many fiberglass shingles are available with colored granules that contain copper. There are enough granules present on each shingle to kill the algae. The copper is slowly released over time. Many of these shingles are guaranteed to kill the algae for the life of the shingle.
To remove the existing stains, you need to use a safe cleaning solution. Believe it or not, there are several treated wood deck cleaners that will do the job without hurting you, the roof, your gutters, and any vegetation below.
Look for deck cleaners that contain bleach. Do not use cleaners that contain chlorine bleach. Oxygen bleach is a non-toxic powder that mixes with water. Do not use a pressure washer. Apply the oxygen bleach solution to a cool roof surface on an overcast day. Do not let the solution dry. If windy or sunny, be sure to continue to apply a light spray of the oxygen bleach solution.
After it has soaked for 30 minutes, brush the solution with a stiff broom or brush. Always aim the rinsing hose down the roof, not up under the shingles. Be sure to wear a safety harness while working on the roof, as wet shingles are very slippery. BE CAREFUL!
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Comments:
Brian 27 Dec 2007, 18:43
Here it is, I think
Barry 14 Apr 2008, 18:16
What is the reasoning behind "do not let the solution dry"? I ask because
I'm considering Spray & Forget no rinse roof and siding cleaner product to
attack this problem. Maybe this is why their cleaner is "patent pending"?
Mark 21 Apr 2008, 08:34
What is the difference between oxygen bleach and chlorine bleach? Can you
tell me the names of each type product?
Kirk 16 Oct 2008, 19:12
I have been a roofer for over 29 years and I would never tell anyone to
scrub their shingles, every time you walk on the roof, you are loosening
the protective granules. Scrubbing or sweeping a roof removes even more
granules and this will only prove to damage your roof further and possibly
affect your shingle warranty. We have found that mixing up some zinc oxide
in a pump sparayer and applying that to a roof or sprinkling zinc and
copper pellets on the roof is the best way to get rid of moss and algae
build-up. To prevent moss and algae, install zinc strip under the ridge cap
with about 2 or more inches to the weather. If your roof is more than a
4-12 pitch, have a qualified roofer install it for you, it won't cost you
any more than a handyman to have it installed and it will be done right.
David 31 Dec 2008, 14:48
Kirk, I like your idea of using zinc oxide to combat roof algae but I
noticed that zinc oxide is nearly insoluble in water. What do you
recommend mixing the zinc oxide in that is safe on the shingles?
gary 14 Apr 2009, 18:17
I have did some roofing in my days and this ALGAE Stains are real but this
all comes from the NAILS that were used to put down the shingles. Last roof
i did we followed the stain and every stain right up to a nail. We should
be going after the nail co,you will not stop the stain only way is to
replace your roof.
Forrest 16 May 2009, 19:04
Gary.....Are you serious ???
I don't pretend to know everything about roofing but have done enough to know if you have nails exposed you have done something terribly wrong!!!!! And if the nails are covered by shingles, as they should be , how does rainwater cause a trail from the nails. The nails should never be exposed to the weather. Sounds like you want jobs replacing roofs !!
Rudy 18 Jun 2009, 01:16
Zinc Oxide is not water soluable, right? what about zinc oxide powder?
Barry 18 Jun 2009, 07:52
The Spray & Forget product I posted about in April 2008 worked! I
liberally sprayed the stained areas and, as directed, forgot about it. Not
sure how long it took but I inspected the area 2-3 months later and the
stains were gone! Looks much better.
ET 23 Sep 2009, 10:40
Black Algae Stains On Asphalt Shingles
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