Henry in MI would know this, (maybe) Hope he sees this.
The gutters thing is an inside joke. Search for gutterless on the main board and you'll find out why we laugh...
I think the stuff could be a resin of some sort. I take it you can't just demo it with a hammer and chisel, how thick is it? How much area are we talking about here? 2sf, 20, 200?
Good luck, hope henry sees it...
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