I have 3 year old asphalt based shingles that are turning black...
mostly in the shaded areas. I assume that it is some kind of mold that
is spreading. Is there anything I can put on it to kill the mold
without hurting the shingles or their original grey color?
My dad used zinc strips on his roof, the mold eventually went away. I
used Jomax on mine, it worked ok. Didn't remove it totally but it looks
nicer than it did.
If you do a groups.google.com search for "mold on shingles" you'll be
greeted with more info than you'd ever care to know.
Bleach will clean it. Try in an inconspicuous area first to make sure it
wont discolor the granules.
To keep it from coming back google zinc mold shingels and read up about
different products. Here is an excerpt from the first google hit.
Q. As I have mold on my roof, would it be wise to install a line of
copper or zinc near the top of the roof and extend it out from under the
last two rows of shingles? Is one or the other preferable? Would doing
this affect the home's white vinyl siding?
A. According to Nick Kerzner, of Kerzner Remodeling & Construction in
Oconomowoc, black or very dark roof stains are caused by a hardy type of
algae, Gloeocapsa magma (often referred to as blue-green algae), which
grows on the roof and feeds on the limestone filler in asphalt shingles.
"The algae often originate in standing water, as well as in lakes and
ponds," Kerzner said. "Wind, birds and other wildlife carry the algae
spores to roofs from the water sources, and then from roof to roof."
Most stains begin on the north-facing side of the roof, where the lack
of sun keeps the roof from drying out completely. The algae normally
grow for quite some time before stains are noticed.
"Five to 10 years is not uncommon," Kerzner said. "As the algae grows,
it holds more moisture on the roof, thus accelerating the growth process."
Installing a zinc or copper strip at the ridge of the roof inhibits the
growth of these organisms by coating the surface with zinc or copper
ions as the rainwater flows over it.
"However, installing a strip will not remove existing stains, so
consider using a product that will clean organic stains," Kerzner said.
"Many of these cleaners are used by power washing the shingles, so
extreme caution should be used, especially on older roofs."
Once the stains are removed, the metal strip should be installed under
the ridge cap, ridge vent or under the first row of shingles for maximum
The strips can stain siding, but the stains are easily removed unless
they're on very old or porous vinyl siding.
"More than likely, any runoff will be contained in the gutters," Kerzner
said. "As for which one is preferable, zinc seems to be the more common,
so availability is easier on ready-to-install products and it will
probably be less visible as it ages."
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I had mold on the sheetrock in my basement, and I thought bleach would
clean it too. I think I killed the mold, but it had no effect on the
black color. Maybe a scrubbrush would have helped instead of sprayer.
I ended up repainting it but that won't work with shingles.
I'll check out the local HD and see what I can find. Are the zinc
strips a common item? If not, where would you suggest I look for them?
Sounds like a combination of things might be needed. I do have a
pressure sprayer but don't want to damage the shingles.
I am in FL and have a tile roof - neighbor has shingle roof. We have a
man who comes around once a year and sprays our roof with a mildewcide
of some kind. It kills the stuff and when it rains after the
treatment, the stain washes off with the rain. Call around and ask
some place like Home Depot. I know they sell it because I bought some
one time and used it to get the mildew stains off my pool deck where
the water ran down from the gutter. Clorox will probably bleach the
stain and won't hurt the color of the shingles...but the mildewcide
will help stop it from growing for awhile.
My house gets those mildew spots on the side of the house where the sun
doesn't reach until later in the day.
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