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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!

Re: early 1950s wall repairs

Not sure what's causing the prolonged curing issue, but......

This might work for you as far as getting a secure patch in the holes; Make the holes large enough (if they aren't already) so that you can use pieces of wood lath to span the holes. Put a temporary screw in each piece for a handle and then weasel the piece into the hole. Send screws right thru the plaster to secure the ends of the lath. Countersink the heads just a tad into the plaster. Remove temp screws and plaster away...including over the countersunk screw-heads.

Re: early 1950s wall repairs

It sounds like what you have is called Rock Lath, which was used as a cheaper and faster alternative to wood lath. It was about 3/8" thick was nailed directly to the studs and replaced the wood lath and base coat of plaster.

Re: early 1950s wall repairs

I agree with Jack. It's probably Rock Lath, which was used after wood lath, but before Blueboard or drywall came along. It came in 16" x 48" sheets and was one of the first building products to use those standard dimensions (in the pre-plywood era).

As for the problems with the drywall compound not drying, use Goldhiller's method for installing backing, then use patching plaster for the first coat, rather than joint compound. Plaster "sets", rather than "dries". Use a spray bottle to mist the area surrounding the hole so that the moisture isn't drawn out of the plaster too quickly. This should assure a good bond to the existing materials. Then use a "setting type" joint compound to finish the repairs. These joint compounds come in bags, rather than buckets. You just mix them with water. They can be easily sanded, unlike plaster.

Re: early 1950s wall repairs

Thanks to all. Now I've half a wit about what I'm looking at. I've already been on the gypsum site and have a mass of info. Thanks again.

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