Mildew on roof

Old 11-04-04, 06:22 PM
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Question Mildew on roof

Can anyone suggest a way to clean the black mildew (I think) that is on my light gray roof? Thanks.
Old 11-04-04, 06:31 PM
shinstr's Avatar
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This will probably sound odd to you , the best way to prevent algae growth is to have a strip of zink installed.

If your roof has older galvanized steel roof vents, you may have noticed that the area directly beneath the vents is free of algae growth. This is due to the zinc coating on the vent.
Strips, made from a zinc alloy, are nailed across the top of the roof near the ridge. These strips release zinc carbonates, which are carried down the roof by rainwater and keep the algae from growing.

The zinc strips will prevent new streaks, but not get rid of existing ones. Clean them with a bleach solution. If you have a steep roof, or are uncomfortable with heights, you could hire a professional roofing contractor to clean it.

Protect your plants below the roof with a plastic tarp. Choose a cool day so the plants don't cook under the tarp.

LIGHTLY scrub the asphalt shingles using a non-metallic brush with a solution of 1 gal. household bleach, 2-1/2 gals. of water, and 1 cup of ammonia-free detergent. (Tide works good) Starting at the top and working your way down, pour the solution on an area and scrub it, being careful not to damage the shingles. Clean the roof in sections and rinse it with a garden hose.
Old 11-04-04, 08:49 PM
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Here is a past post:
I'm sure it's algae.
This is a question that is answered here in great detail on here quite often.

I LOVE this site, but it's "search" function leave alot to be desired.
I have tried looking for some of the earlier answers, have had no luck.

In short, it can be cleaned with a 1/3 water, 1/3 TSP (detergent), and 1/3 bleach mix.
Actually, the more bleach, the better....however, your landscaping around the house doesn't like bleach. That is why they say to dilute it with water.

Spray the mixture on the algae and let it sit for 15 minutes or so.
Then rinse it off with the water hose.
Douse your plants in the yard before your spray the roof to dilute with any runoff from your roof.

You may have to re-apply depending on how bad the algae is.

You could pay to have it done.
Do NOT get anyone that uses "high-pressure" washing.
It will knock the granules off the shingles.
Use only a "low-pressure" wash.

I wish I had more time to elaborate, but I've got to go.
Maybe you could have more luck with a search on this topic here.

Good luck.
Old 11-05-04, 11:31 AM
Ed Imeduc's Avatar
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Location: Mountain Williams Missouri
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Down here where we have it all the time The best way I find. Get a ortho hose spray. Set if for the top 8oz. Go and get swimming pool chlorine thats 10% where the clorox is only 5% to 6%. Just spray it when ever it comes back.


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