Walls and Ceilings - Dry Wall over Plaster Wall?

I have plaster walls.
My house is about 120 years old.
As I take down the wall paper, some spots in the wall crumble to the point where I can see the wood slats in behind.
I dont really have the time to knock out all the walls and dry wall it so I was wondering about putting dry wall over top of the plaster. Im worried that:

A) It will make the rooms look smaller all the way around.

and

B) If I dry wall over plaster and go to nail into the dry wall to hang a picture, I will hear the plaster in behind crumble.

If the plaster in the wall did crumble, would the dry wall still hold up? :eek:

I have done this and in answer to your questions, my experience has been 1) yes it makes the room slightly smaller, but not noticeably so, 2) the plaster does not crumble when I put a nail or screw in, or at least I don't hear it, probably becasue the drwyall is to some extent holding it up. 3) I don't know about the longterm likliehood of the plaster crumbling enough to casue probelms with the drywall, but I haven't had this happen in the short term(the work was done two years ago). My thinking is that the plaster is not likely to crumble a great deal after is is covered, becasue the drywall is protecting it from impact and physically holding the plaster to the lathe (wood) behind it. The reason it is falling off in the first place is that originally, it was attached to this wood lathe by pieces of plaster (keys) fromed by the plasterer pushing the first coat of plaster through the cracks between lathe strips. As the plaster ages, these keys break off, often when the surface is intact, releasing the plaster from the lathe. You then have a bubble which is very susceptible to cracking from any impact or it's own weight.

One problem you will run into is that the new drywall will interfere with existing moldings. If you want it to look good you will likely have to pull the moldings and shim as necessary. Another problem is that any large bulges or gaps in the plaster may telegraph through the new drywall. You can get around this by puttting up thin pieces of wood ie. 1x2 or 2x2 over the plaster on top of the existing studs (I think they are called sleepers, but I am probably wrong). This will of course require even thicker shims under the mouldings

There is also always the option of repairing the plaster, which I have also used. This does not require removing the moldings and you can retain the look of plaster (ie. less than perfectly flat). It is cheaper, although perhaps slightly more time consuming than covering with drywall, but not a great deal. If you are interested in the latter option, write back.

Bruce

Thank you for your advice