Did you wet the roof first? I would have started with a weaker Chem strength and rinsed extremely well, there is a chance that you lightened the natural color of the shingles permanently. I hope this is not the case.
-- Edited by Zach Maynard on Sunday 17th of November 2013 01:45:37 PM
Don't think you necessarily did anything wrong, just looks like F9 cleaned the shingles where it was applied. If home owner is concerned, I would just clean the rest of the roof with you usual roof mix, not F9.
Definitely prewet before treating, then start with like 30 percent strength and progress in strength as needed. Usually 50/50 does the trick. Then rinse really really really well. We usually like to "feather in" the area surrounding the stain so any change in color is progressive and not noticeable.
Always clean the roof or the surface around the rust at least wall to wall on siding or gable to gable on roof. Its no different than if you sell a roof cleaning and they have a deck - always give the option to clean the deck because there will be clean spots. Even if they say no, I clean the deck anyways because it will look funny. If they didnt want to pay for cleaning the roof, clean it anyways and then their "charge" is to leave you a good review on angies list or google review as a favor.
When cleaning rust on shingles, always pre wet the surface. Using 3 parts water to 1 part F9 apply to shingles, let dwell a couple minutes, don't let it dry, rinse after each application, and after you final application and all the rust is gone, apply a mixture of Green Wash and water to neutralize.
When cleaning rust on shingles, always pre wet the surface. Using 3 parts water to 1 part F9 apply to shingles, let dwell a couple minutes, don't let it dry, rinse after each application, and after you final application and all the rust is gone, apply a mixture of Green Wash and water to neutralize.
I like Doug's approach here for shingles. It's better to use a diluted strength and take your time. Treat it like a restoration rather than going straight in for the kill. Once you have your dilution and methods down, you can increase the strength to suit how much time you can spend on the job. The more you use F9, the better you will get and know how strong you should be applying it.
Just like with concrete, you should always use light mist sprays and feather the product out 2-3 feet going lighter the farther away you are from the original rust stain. This will make it blend should there be any color issues afterwards.. which may happen but are rare.
Here is the link for dilution ratios and technical data: Best Rust Remover
-- Edited by Craig Harrison on Sunday 24th of November 2013 04:53:49 PM