Or maybe vice versa would make more sense as that would imply that the sheetrock is new and the lath and plaster old (duhhh).

Nice house in Marin, I'm guessing 20s or 30s - lath and plaster - studs are 3.75 x 2 - knob and tube wiring. I'm knocking out one wall to merge the master bedroom in Unit A with the bedroom in Unit B. This is about the nicest 2 unit house I've ever seen, not a duplex - unit A is a deluxe 2 bedroom while unit B is a deluxe studio.

I'll have to heal over the stub where the old wall and ceiling were and I damn sure don't want to shorten an apprenticeship at lath and plaster from 2 years to 3 days.

My first instinct is to use paper and hot mud over the joint tween the plaster and the rock, and sand and re-coat like I was enjoying myself.

__________________
Te futueo et caballum tuum

1986 300SDL, 362K
1984 300D, 138K

Seems to me that it's going to be very hard to make the wall and ceiling look seamless. Any chance of some kind of moulding at the joint to hide it?

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

It sounds like a good opportunity to make a master bedroom suite, put a pair of french doors in there........
If the plaster is smooth and not too rippley then you shouldn't have a problem fixing a gap of that size. You should be able to skim coat the repair area and have it be pretty much completely hidden.

I floated the idea of putting a modest arch sort of transition at the joint. I checked the attic and the wall isn't load bearing - well it was a tiny amount - the roof rafter above it had a 3 foot small post resting on the top plate (not a steep roof) - the rest had one brace going from center of rafter over to the plate at the top of the common wall, the one that will stay in place - dining room on other side. So I added a brace. If I had needed to put in a triple 2x12 or something to support major weight, I'd have been off the hook for the seamless merge.

Oh well, should be interesting and I'll take pictures.

__________________
Te futueo et caballum tuum

1986 300SDL, 362K
1984 300D, 138K

Fine Homebuilding, January 2010 has an article for fixing damaged plaster walls that is pretty comprehensive

I've done some of this working on an 1860's wood frame townhouse-

When I took down walls, I used a circular saw set for the depth of the plaster, and cut the plaster into squares. This way the plaster can be removed and then you can remove the lath (if its wood) so you can save it to fix holes. Dont just go at it with a sledge, as you will break plaster keys elsewhere and end up with loose plaster on the walls and ceiling

Where the walls meet (the stub) there will be no lath, and this is where after removing the corner studs you can use the old lath to fur out the new gyp. board. Build up to the plaster surface with gyp. board so the mud is minimal. Paint the edges of the plaster with Plaster Weld- it is pepto bismol pink and acts as a primer to the plaster so the plaster does not suck all the moisture out of the mud. Use fiberglass mesh to bridge over the whole area and skim coat.

__________________
95 E300D gave away
77 300D, 227k, station car
83 300CD 370k, body gone away to the rust gods, engine is in a Yota pickup, going strong
89 190E 2.6- 335k, no more
79 VW FI Bus- 154k summer driver
59 VW Beetle ragtop- 175k
12 VW Jetta- 250k
74 MG Midget-78k

Dude, I hope you are getting those materials tested, old plasters can be full of asbestos, 20's, 30's vintage is lousy with the stuff. As long as it is undisturbed, it is considered safe, but once you disturb it......

If you can afford it putting a half inch of drywall over the whole ceiling makes a lot of sense. Patching the trench will be very hard to make nice. The expansion and contraction will probably crack the patch too.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

That's a good call, I'll look into it.

__________________
Te futueo et caballum tuum

1986 300SDL, 362K
1984 300D, 138K

Excellent advice. I have boxes of older issues of Fine Homebuilding but the trick is having the index. I seem to recall that's in the last issue every year. At any rate, I'll look for that one at a library.

It looks like I'll need to get a sheet of 1/4 and 3/8 sheetrock so as to patch in where needed.

__________________
Te futueo et caballum tuum

1986 300SDL, 362K
1984 300D, 138K

If it has wood lath I would expect to find horse hair in it instead of asbestos.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

It might be easier to meld LATH and plaster to sheetrock than lathE and plaster. Not quite so lumpy.