I've been searching and searching and learning more as I go, but have reached the end of the search button road. I still have a couple questions about how the 3% SH will react.
I've been called to wash a Hendricks Tile roof, which is no problem in itself. The issue is that it is a mansard style roof with recessed windows in the mansards which are flashed on both sides and the bottom with what appears to be patina'd copper.
Neither the lady living there or I know if it is true copper or lead coated copper. One of my questions is: does copper react differently short term or long term than lead coated copper???? HOW can I tell the difference by looking at it? Is that possible?
Also, the exterior window frames around the windows are aluminum made to look like wood. How is 3% going to affect them?
In the past, I've seen the splashing of the SH landing on a copper surface just below a white aluminum frame window turn the lower portion of it a dark charcoal grey.
Bill Booz had a comment in a thread that linked reactions with various chemicals and surfaces. I couldn't find it, but it may give a little info.
I had a customer that told me he didn't care if we speckled his moderately petina'd copper. That was him...but he had a wife living there too so we played it safe and protected it the best we could anyway. It was a house wash so we cleaned the siding under the copper, then continually rinsed the copper with Final Wash at a higher setting while cleaning the siding above the copper. The FW stopped the copper from getting speckled from the SH, but that was house wash mix, not roof strength. Could you cover the copper with plastic to protect it as well? I couldn't do that on my job due to the design of the house so FW was the next best thing.
As a last ditch effort before walking away, see if they would be opposed to having some spots on the copper from the SH. Or they may prefer to have someone come out and clean the copper and restore the original copper shine to the surface versus the petina.