Removing stains from house roof shingles

[Bob]

I had ugly black stains on my roof shingles. I read up on it and first used oxalic acid. That didn't work and I tried household bleach. The black stains disappeared but left an ugly light brown stain in its place. I tried bleach twice more. The last time I used nearly full strength bleach. Before the bleach could dry (I did this in the early morning before the sun hit the roof), I washed the bleach off with a hose. The brown is still there; looks worse than the black mold because the light brown really stands out against the dark shingles. It makes the whole house look shabby.

Now I'm getting really frustrated. I didn't want to use a power washer but I feel that I'm left with no choices. I use a 40 degree tip (the widest tip) on the power washer angling down on the shingles (never pointing up the roof). The power washer is extremely powerful so I don't want to get too close and damage the shingles. The power washer does reduce the brown stains somewhat. In the higher elevations of the roof where I didn't want to spray up and get water under the shingles, the brown looks positively awful.

I believe that my original mistake was not rinsing the bleach off on the first pass and I caused the brown stain to become permanent.

Does anyone have any suggestions on how to proceed from here?

[meek mike]

quoting my post from last month in thread about power washers:

I live in Houston, a swamp of algae and mildew, so my 'new' house has some algae on the bricks. I wanted to try chemical removal first before pressure washing. I'm not certain if bleach will have any effect on algae (as it does on mildew). I browsed at Lowe's and found several spray-on cleaners for houses. Then I found this stuff at Ace Hardware:

specifically for algae. It was expensive per gallon but it seems to work well at killing the stuff, plus it leaves a residue that keeps the stuff from growing back. It doesn't have the immediate effect that power washing would but then power washing can damage siding, etc. (update: this is cool stuff, it's working well).

Check out their website, they show some machine to spray roofs. Don't know about the bleaching effect from the bleach, could be permanent.

[ROBMURR]

You should have used M1 roof and deck cleaner from Home Depot with a small pressure washer with 40 degree tip. You have nothing to lose try it now.

[m Ransley]

Are you sure the brown isnt the tar comming up, you need to show it to someone that knows before you make it possibly worse.

[Bob]

I had ugly black stains on my roof shingles. I read up on it and first used oxalic acid. That didn't work and I tried household bleach. The black stains disappeared but left an ugly light brown stain in its place. I tried bleach twice more. The last time I used nearly full strength bleach. Before the bleach could dry (I did this in the early morning before the sun hit the roof), I washed the bleach off with a hose. The brown is still there; looks worse than the black mold because the light brown really stands out against the dark shingles. It makes the whole house look shabby.

Now I'm getting really frustrated. I didn't want to use a power washer but I feel that I'm left with no choices. I use a 40 degree tip (the widest tip) on the power washer angling down on the shingles (never pointing up the roof). The power washer is extremely powerful so I don't want to get too close and damage the shingles. The power washer does reduce the brown stains somewhat. In the higher elevations of the roof where I didn't want to spray up and get water under the shingles, the brown looks positively awful.

I believe that my original mistake was not rinsing the bleach off on the first pass and I caused the brown stain to become permanent.

Does anyone have any suggestions on how to proceed from here?

[Bob]

No, it's not the tar. I got a little bit more aggressive with the power washer and I was able to further reduce the brown stain.

I'm going to try some of the products that other posters have suggested.