Don't know if anyone can help but if so could be a big money spinner. Do you
find marks of small rough circles on your customer windows and you can't get
them off. Have tried but customers are now taliking about getting new windows.
I spoke to a builder about this and apparently it is the glue that adheres
the stones to the walls, when it rains it runs down the windows. Hence
the marks on the windows.
Any substance you know of take this off.
Cheers
Doug