Ashley Phillips
Moderator
I think this is carbon build up from the road with some mold on it. We have tried Bleach, HCL will eat it off but leaves it kinda orange, and 4 different products from Prosoco. The sales rep from Prosoco said to try their concrete cleaner but we haven't done it yet.
They are 3 stories tall and there are 174 limestone blocks under the windows.
They are 3 stories tall and there are 174 limestone blocks under the windows.