Dan I have been trying to remove soot for three years and have tryed many products. I can't tell you how many times I heard " this will take it off for sure ". Since your in PA you must see it, do you know how to spot it before you clean the roof?
Our quote and warranty states that rust stain removal is not in our scope of work, as proposed. The HO is not all that happy because he has not paid, but he has a reason not to be happy with the results. I'm have offered try some OA, Rust Must and Iron Out at no charge, also getting a sample from Prosoco for rust and metallic cleaning. This job was about 1K, so it would be nice to have a happy client and the job paid for. One consideration is that there was so much granule loss on one part of the roof that all of the red color was totally gone. Roof was cleaned 1 time prior, HO's said it was no pressure wash?
A old time cleaner called them "iron stains", he cleans a lot of old churches, schools, historical limestone restorations, he said that nothing I could put on the roof would cause damage in terms of above, He said OA might do it, but if the shingle has soaked up that the iron rust has covered the red up.
Lesson learned is that I will pay much more attention to future work with anything metal that could present the same kind of problem, this experience will make us note this potential to prospective HO's prior to my next start.
I did use some CLR on a rust stain from a electric service pole on an older home the other day and it removed about 75% and diluted the remaining to the point where I was surprised, white shingle too boot.
The roof is absent of what we say we will remove, but a stain is a stain to some people. I know that I'am doing all I can do to make HO happy. I will post a pic of some bare naked shingle's tomorrow.
Ya we definitely have chimneys in these parts, how do you spot the soot? I know a lot of ppl have the direct tv satellites, I have to be careful, making sure there is no rust by them.