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Hey Anthony,...like Scott,..I've never seen this before,...but, also as Scott said try oxalic,..and although common thinking is always start weak and go stronger,...I think it is going to take a stronger mix,....just looks like it could be tough. Give it time to work as well.

Jeff

Thanks for the replies guys.

So you guys think it would be on the acidic side and not the caustic side of chems? It's not rust, it's runoff from raining on aging clay tiles.

Would cleaning the roof help in reducing this type of problem from reoccurring? I haven't ran into this yet, but it might be good information to know...

I have come across this a couple of times now.

If it is residue from the tiles, and yes they do "leech" red when acidic rain or an over zealous PW gets to them, it will come off without to much effort.

However, if it has etched or stained the paint due to the paint being chalky then theres not much you can do that won't leave some evidence behind.

I have had sucess believe it or not with 1 quart amonyx lo in 50 gallons of water and about 4 cups of sodium bicarbonate. I used my soft wash sytem to apply the "soap" let dwell until it is almost dry and then remove with your PW and a 2510 or 4010 tip. Tips size depends of course on the psi and gpm of your machine. But you basically are looking for 1200 to 1500 psi at 5 to 6 gpm.

The soap will help lift the residue as if it were any other dirt.