While in the loft I lifted some of the insulation to find that virtually all
the 'key' bits of plaster that squish through the lath were detached and
just littering the surface. However the ceilings seem to be staying put. I
can't think what's holding them up! Do I have a serious problem please? The
house is 1930's.
Is it possible the ceilings have been plasterboarded at some time?
This is often put directly over the top of the old lath and plaster?
From below, can you push the ceiling and feel a "live" movement? If
so, then they are probably held up by luck ;-)
Remove HAT before replying
There's a serious potential problem, aye. I think it's the plaster
equivalent of surface tension holding the ceiling up - if it's damaged
at any point it could cause a collapse.
All is not lost though. Since you obviously have access to the laths
themselves you can repair the ceiling from behind by using a form of
plaster of paris. I don't know how expensive that might end up being
but if you've got any original decorative features on the ceiling its
pretty much the only way I've heard of keeping 'em intact.
Here's a bit of detail:
I've also read about 'plaster washers' which screw into the joist to
support the ceiling and can be replastered over, but that seems to be
more a US thing.
Here's another one:
I'm going to have to revisit this in our dining room - after I removed
a parting wall (none load bearing) the ceiling looked decidedly
unhappy so its held up with battens screwed to the joists on either
side of where the wall was!
What makes you think the plaster is not bonded to the lath ? After all,
that's all there was to hold it up until the "nibs" dried.
Slightly more seriously, the ceiling will be weakened by losing a
significant amount of the "nibs" that do provide some structural strength.
As long as you don't start having parties in the attic, it'll be fine. Try
to walk around on the joists carefully if you don't have anything lying on
them to spread the load.
It might be for first few days, but after a few humidity changes,
it certainly won't be. Someone may have already fixed it by pouring
diluted PVA over the laths and plaster, which will bond them.
If not, that's something you might do, but I wouldn't risk it
without supporting the ceiling from underneath while it dries.
This is a common way of repairing a lath and plaster ceiling
once the plaster does come away from the laths, providing it
hasn't fallen down yet. A board supported by some slightly
over-long poles is used to push it back in place, and diluted
PVA poured over the back to soak in and set.
The adhesion between the old plaster and the laths is amazing and it is
highly unlikely that it will come down around your ears. With all that old
horse and goat hair spread through it, it is even more amazing how the got
it up on the ceiling in the first place. :-))
I doubt it - if you open up the bottom of a lath and plaster wall you'll
find it full of these 'nibs'. The plaster sticks to the wood laths.
The easy way to tell if it's gone 'live' is by pushing it between the
joists. One in good condition will be firm - a poor one will bend easily.
*Never miss a good chance to shut up *
Dave Plowman email@example.com London SW 12
As a temporary expedient some years ago I propped up a lath and plaster
ceiling with acrow props and 8 x 4 chipboard, and poured neat sloppy plaster
under the upstairs floor boards to hold it all together. When I came to pull
it all down a few months later it was VERY well bonded !
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