Dave Baker wrote:
Probably the original horsehair, rat dung and sea shell plaster that my similar
aged house is afflicted with. Nothing lasts for ever and plaster "blows" in
patches in older houses. I'm sure by the time modern ones are 70 years old
it'll be happening to them too. Tap the walls with a knuckle and where it's
blown you'll get a dull sound. You can just rake those bits out and patch them
up again if the rest of the wall is sound. There may well be damp of course but
that needs checking for separately.

I've come to the same opinion as well. Since the problem affects the
whole of that side of the house, uniformly from the floor downstairs to
the ceiling upstairs, it can't be primarily caused by damp. I'd expect
it to only affect the lower areas of the walls in patches if it was
damp. So hopefully it's just crap old plaster. It's just odd that it
only affects the one side of the house....

Thanks,
-Duncan