Rust Stain on Asphalt Shingles

[powersdov]

Does anybody know how to remove rust stains from asphalt shingles? I have to vents that have left rust streaks running all the way down the roof to the gutters. I have light gray shingles.

[ransley]

An acid cleaner like CLR might work, I dont know if it will damage shingles.

[pipedown]

Stop the source of the rust perhaps by painting or replacing the nails (with copper) and the stains will fade in a year or two. The rust stain is just particles trapped on the shingle surface not actual rusting of the shingle so a rust cleaner like CLR will have limited effect (except by virtue of the soap it also contains). Plain old dish soap and a garden hose would be how I would start. Don't spray too hard or the grit will come off too much and you'll wish you had left it alone.

[Boden]

You can remove the rust stains easily with oxalic acid. But, first you must eliminte the source of the rust or they will re-occur.

[powersdov]

Thanks for the advice. I have already taken care of the rust with some black rustoleum. Where can I buy some oxalic acid?

[Boden]

A good hardware or paint store will have oxalic acid. It is used and sold as wood bleach. Oxalic acid, dissolved in water will react with the (insoluble) red iron oxides that we call rust to form iron oxalate which is soluble in water and therefore just washes of. You will need to keep the area you are trying to clean wet with the oxalic acid solution until the rust stain disappears. Protect any bare wood or it will be bleached. Although found in most green leafy vegetables in small quantities oxalic acid is poisonous.

As an aside, I have considerable iron in my water. The housings of my water filters get to look pretty gross when as they turn brown with rust. Last week I took one off, dropped it in a bucket filled with water and about a quarter cup of oxalic acid. About an hour later I had a crystal clear water filter housing.

Good luck.