stain removal on cast stone

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Author Message David Axt, AIA, CCS, CSI Senior Member Username: david_axt Post Number: 1256 Registered: 03-2002 Posted on Thursday, October 20, 2011 - 12:18 pm:    I am currently working on a historic renovation project where there is staining on the cast stone panels. Since the staining only appears on the window spandrel panels, I suspect the culprit to be window washing chemicals. I bet the professional window washers used a silicone oil type window treatment similar to Rain-X for auto windshields. We have been doing prebid cleaning mockups and have removed dirt, grime and biological growth but can't remove this "wet" looking stain. Any ideas would be appreciated. Lynn Javoroski FCSI CCS LEEDŽ AP SCIP Affiliate Senior Member Username: lynn_javoroski Post Number: 1320 Registered: 07-2002 Posted on Thursday, October 20, 2011 - 12:27 pm:    Call American Building Restoration Products, Diedrich Technologies, or Prosoco (all are on 4specs under Masonry Restoration...). If one of them doesn't have a product that will clean the stain, I think you're only solution is to replace the stone! Seriously, these companies should have a product that will solve this. Jim Sliff Senior Member Username: jim_sliff Post Number: 106 Registered: 08-2010 Posted on Monday, October 31, 2011 - 06:52 pm:    What Lynn said. I have a long-term project in L.A. (phase after phase of waterproofing) that is a high-rise building with stone panels up to 22 stories, many badly stained. Just about everyone under the sun has tested something or other to try to remove the stains and nothing has worked. They've more or less resigned themselves to living with it - replacing the stone is cost prohibitive and coated the stuff looks worse. J. Peter Jordan (Unregistered Guest) Unregistered guest Posted on Tuesday, November 01, 2011 - 10:12 am:    I can't help but throw in a remark about a building's patina and observe that one person's stain is another person's patina. I would hope that the people on this forum understand the difference between the weathering of a building (which may include a certain amount of staining) and a stain, but it is not always clear. On the original question from Mr. Axt, I would suggest that silicone sealant used around the windows is to blame. This is not really a "stain" but the silicones in the sealant bleeding into the cast stone which would account for the "wet look." This probably made it easier to clean the dirt off of these areas. There are several manufacturers that make products that go on as a paste and soak up stuff from the substrate. Don't know if that would work in this case.