Mike, I'm not a construction expert, but have lived in a house with similar material for 25 years. Mine was built in 1952. I think it was the last gasp of plastering before construction switched over to drywall techniques. It makes for a wonderfully solid, well sealed wall/ceiling structure. But it is a real b*.%* to do any remodeling with. A recent kitchen project had me installing can lights in the ceiling. The plugs removed measured from 7/8" to 1" thick, and had the consistancy of cement. And as you can imagine any patching has to be custom made to fit. Also has a tendency to develop hairline cracks. I guess that's why a former owner had covered all wall and ceiling surfaces with painter's cloth which I have removed and sanded walls smooth during remodeling.