We cleaned this limestone chimney today. Soft washed it with about 8 coats of 50/50 SH, even washed some spots with straight SH. It was soaking for about 75 minutes in total. I’m pretty happy with it overall, but the blackest spots from the before picture can still be seen as greenish spots in the after picture.
Is there any way to clean the rest of the discoloration, or is some of it permanent at this point?
Thanks for your help!