black streaks

Old 12-21-04, 09:44 AM
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black streaks

Merry Christmas,

I have black streaks running down the asphalt roof. What is this?

Old 12-21-04, 09:51 AM
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Many thing
if your close to airport its a mixture of rain and sout from plane.
could be rain and asphalt burn up from the summer heat.
or if its thick and runny might be roofing cement

Old 12-21-04, 07:04 PM
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There have been many, MANY, questions like this posted here for a long time.
I have explained this over and over again. I would do it now, but unfortunately, I have a broken arm and typing is not easy for me right now.

I tried to do a "search" for my other posts on this, but this forum format is not very user friendly. I could not find it.
Maybe you'll have better luck.

In a nutshell, most likely you have a form of algae that is in the air. It will eventually turn your roof black. It can be cleaned off with a low pressure wash system that will not hurt the shingles.

I'll try to answer in detail when I have a ton of time or my arm gets better.
Old 01-02-05, 09:31 PM
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There is research that indicates that often the black streaks found on roofs are caused by an algae. This tends to be more of a problem on light colored roofs or vibrant colored shingles. Algae tends to grow in humid environments, especially on the north side of the house where there tends to be more shade & moisture. The algae feeds on minerals in the asphalt shingles. Asphalt shingles also tend to hold moisture longer, making for a happy environment for the algae. By the time you notice the algae, it has been there for a very long time because it take a while for the dead, black algae cells to build up. Algae does not affect durability of the shingles, but it tends to be unsightly & worry homeowners. The algae cells are airborne and can be carried from roof to roof in a neighborhood. Cleaning provides a temporary fix because algae will return. Cleaning can be expensive and damaging to roof. There are algae resistant roofing materials available today.
Old 01-03-05, 07:29 AM
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Originally Posted by twelvepole
Cleaning can be expensive and damaging to roof.
Yes, it can be damaging if it isn't done correctly.
However, there are ways to clean the roof without damaging it.

The rest of the post is dead-on correct.
Nice post, twelvepole.

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