Please see picture attached. This is limestone on a school and i have tried everything to get the black streaks out. i have tried 12% sh with a little green wash. I have tried 4000 psi which only started to take the surface off. I have tried other asids and gutter cleaner. it looks like its black algae but just wont come out. i have let the solutions sit over night after several application and still results are the same. Any idea of what would work
maybe try one restore by eco chem. Have you tried hot water
Mike Laskowski said
Sep 11, 2012
Josh, limestone is a porous stone that needs care not to use the wrong chemical (no acids) or to much pressure. For Limestone cleaning it is recommended not to exceed 900 psi because limestone can be damaged at pressures above this pressure. As far as chemicals, limestone can be cleaned by the SH/Green Wash mix if the stain is organic in nature but since you already tried this approach I have heard of another stain removing technique using a "poultice." It should be noted that I have never performed this technique but wanted to give you an option to look into. Your local hardware store should sell a poultice cleaning solution for cleaning limestone surfaces. A poultice is a powdered substance that is mixed with water and smeared over the stain. The cleaner should come with directions. I would definately test this out on a small area first.
Good Luck and let me know how it works out!
Josh Scavetta said
Sep 11, 2012
yea i tried one restore and it didn't have any effect. i should had mentioned that. thanks mike ill look more into that poultice product
John Smith said
Sep 11, 2012
I wonder if its from decomposed flat roofing. Seems to be darkest at the top. Maybe a company that makes that type of roofing might be able to help.
John Smith said
Sep 11, 2012
If it is to porous it might need to be lightly sand blasted
Jason Heath said
Sep 11, 2012
Have tested a strong degreaser?
Gregg Austensen said
Sep 11, 2012
Have you been on the roof if so what is tr covering. It looks like there is a drainage issue up there and the stains could be from the covering as water sheds off. I'd think about trying a enzyme based degreaser that will eat hydrocarbons like what you'd use on a garage floor to eat oil stains.
Hope it helps.
Ryan Freidline said
Sep 12, 2012
looks like roof bleeding. Is there an oil based roof on top, like tar? try gasoline and a sponge, or an oil emulsifier of some sort....
Mario Ciottariello said
Dec 28, 2013
What ever happend to this job .did you get the stain out and what did you use.thanks
Please see picture attached. This is limestone on a school and i have tried everything to get the black streaks out. i have tried 12% sh with a little green wash. I have tried 4000 psi which only started to take the surface off. I have tried other asids and gutter cleaner. it looks like its black algae but just wont come out. i have let the solutions sit over night after several application and still results are the same. Any idea of what would work
Josh, limestone is a porous stone that needs care not to use the wrong chemical (no acids) or to much pressure. For Limestone cleaning it is recommended not to exceed 900 psi because limestone can be damaged at pressures above this pressure. As far as chemicals, limestone can be cleaned by the SH/Green Wash mix if the stain is organic in nature but since you already tried this approach I have heard of another stain removing technique using a "poultice." It should be noted that I have never performed this technique but wanted to give you an option to look into. Your local hardware store should sell a poultice cleaning solution for cleaning limestone surfaces. A poultice is a powdered substance that is mixed with water and smeared over the stain. The cleaner should come with directions. I would definately test this out on a small area first.
Good Luck and let me know how it works out!