WLN: I have no issues with him, just that portion of his technique you shared (the chisel) and with his understanding of limestone.
SC: If you're unhappy with his conclusion then, if you can, get your own research done.
As matters presently stand (whether you like or agree with it or not), the marks on that roof block have been painted onto a layer of calcium sulphate - plaster.
Edited 1 time(s). Last edit at 10-Feb-19 19:37 by Scott Creighton.