Hello Everyone, I got a call to bid a building cleaning that has black stains that appear to be running down from the Aluminum Window Frames onto the Sides of this building. Some are like shadows and some are very black. When I look very close it is the cement/grout that is holding the aggregate onto the wall that is dark. I tried some chemicals but it was getting dark yesterday and I will go back today and try some more. Has anyone cleaned something like this before? What worked for them? Thanks for any help.