early 1950s wall repairs
I've stuck my neck out and now I'm up to my eyeballs in trouble. The problem is this house was built in the transition period from lath and plaster to gypsum board. The interior walls appear to be plaster on top of a plaster mud then covered with base coat and skim coats of plaster. The mud is like compressed sand, solid but when scratched with a knife it falls away like sand. It appears to be porous. There is a paper on the back against the studs but nothing on the plaster side. It appears to be as much as 3/4" thick although I cannot see the seam between the mud and the plaster. It's as if it was made specifically for plasterers, not drywallers.
I'm having electricians come in to replace the knob and tube wiring and they're going to have a field day making holes through the house. I have to go around and patch all of these holes. I've searched everywhere I can think to find what I've got and what to do about it. Nada, niet nut'in.
Anybody think they know what I've got? What can I use to affect repairs? I've experimented with Duracoat 20 and it still takes several days to cure out to the sanding stage and the bond is not terribly solid. Plugging holes with gyprock and drywall compound seems to exacerbate the issue. They never seem to cure out even after a week.
Relative humidity right now is about 70-80% and temperature is in the low to mid 30s C. (high 80s, low 90s F.)
Help! My wife is getting the renovation blues and I'm getting it in the neck!