RBM (remove this) wrote:
Plaster walls and ceilings from the 20's would most likely be wood lathe.
After many years, the plaster squished between the lathe,(keys), falls off,
and the plaster looses much integrity and cracks and falls off. Papering
over it helps to keep it intact, and I'm sure you can patch and repaper to
keep it looking decent. Ideally, removing the plaster and lathe and
installing sheetrock would be a good solution, or sometimes you can have a
3/8" layer of sheetrock installed over the plaster.
.....

OTOH, I've worked on refurbishment projects of many houses from the
_18_20's where the plaster is still in excellent condition. For a
plaster job of less than 100 years to be in that bad of shape implies
it wasn't very good to begin with.

As someone else noted, impossible to say much from the information
provided for a particular case. Personally, I'd be prone to keeping
the existing plaster and repairing it unless there's far more evidence
than a few spots here or there.

I also agree w/ the assessment it's far better to go to the trouble of
removing the wallpaper down to a solid surface and then make the
decision of whether to paint or re-paper. If going to the effort to
begin with, really can't see the point of not doing it right to begin
with.