Proper usage of f9

Hey guys. I wanted to know when you use f9 on a roof that is damaged by chimney caps (large rust stain). Do you just spray and walk away or do you wash it with water after it works. And if you are only removing rust stains is their a noticable difference in the roof shingles where you sprayed the f9 compared to the rest of the roof. Thanks
 
These guy are right on the money and use a lot of the best rust remover. You can usually dilute F9 BARC down a bit too. Rust is composed differently depending on where you are but some guy are using with as much as a 1:4 ratio (1 part F9 to 4 parts water). Most are around a 1:2 or 1:3 for stucco, siding and shingles.
 
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