We pressure washed the slate roof with water at the level of steam, with cleaning the stone exterior with hot water.
The roof turned out beautiful, but the soil has ran down the stone for 80 years. We were able to remove everything from the stone, but the staining will remain for a year or two. If the sun light can not see the direct surface the staining remains, but now the sun can see the stain, so the ultraviolet rays of the sun will oxidize the staining and the rain will wash it away. We believe in doing everything natural and not use chemical that will destroy.
Someone replaced the slate below that piece of metal by pounding a hole through the top of the slate above and then slid a thin piece of aluminum under it and passed the hole to keep water out. When a large wind comes up and vibrates the slate the metal will slide out and the homeowner will have a leak in there home. We took out everything and replaced the slates the correct way! We found over 60 slates on this roof done this way.
I never seen this before. Someone took slates and stuck them to a piece of rubber, then laid it over the top of the roof, nailed it on and then caulked the nail holes to hold it to the house. I just can’t believe the thing people do, they have to know this is just wrong. We ripped all of this out and put a new slate ridge on and I bet what we did correct was much faster.