[ACSTravis]

I have a restaurant that I do flatwork for that has a border running all around the top of the building under the gutter made of dryvit. It has black streaks on it and they would like it cleaned. I realize dryvit is very soft and you can't use any pressure on it. So, what I would like to do is downstream something onto it and rinse it off. Can anyone help me out with a recipe of something I can downstream? Thanks a lot,