1920s house, lath and plaster ceiling in the front bedroom. Three separate hairline cracks running roughly parallel, each about a metre long. I've filled them with flexible filler and repainted twice over two years and they always reappear within a few months, in exactly the same lines. Nothing feels loose when I push on the ceiling. What's the actual fix here?
Also resist the advice to pull it all down and board it. It's a legitimate option and sometimes the right one, but a sound lath ceiling with two detached patches is a repair job, not a replacement job, and the acoustic and thermal behaviour of the original is better than most people expect.
Flexible filler is the wrong material regardless. On plaster you want either a proper plaster filler or, for anything wider than a hairline, scrim tape and a skim. Flexible fillers stay softer than the surrounding surface and telegraph every movement straight through the paint.
Before you commit to that, tap along the crack with your knuckle and listen. Solid sound means the plaster is still keyed and the crack is probably just movement. Hollow or drummy means it's detached and the washers are the right call.
Then treat the two hollow ones properly and the third one probably just needs scrim and skim. Don't be surprised if the hollow area is larger than the crack — tap the whole ceiling and mark the boundary with chalk before you start.
Definitely hollow either side of two of the cracks, solid on the third.
One thing worth ruling out cheaply: is there a bath, a heavy wardrobe or a new bed frame directly above those lines? A hundred year old ceiling can start cracking after a change in the loading pattern above it, and the fix is different if that's what's driving it.
@immutable_infra · 3mo ago · 3 replies
Parallel cracks a metre long in a lath ceiling are usually following the joists, and what's cracking is the plaster keys — the blobs that squeeze through the gaps between laths and hold the whole thing up. Filler on the surface does nothing about that, which is exactly why it comes back in the same lines every time.
Go into the loft or floor above if you can and look at the top of the ceiling. If you see a lot of broken key material lying loose on the laths, you've got a section that's slowly detaching. The fix from above is to reattach the plaster with plaster washers and screws into the joists, or to run a bonding coat over the top of the laths.
If you can't get access above, the from-below fix is plaster washers on drywall screws driven up into the joists, spaced along the crack line, then scrim tape and a skim coat over the top. Ugly to do, permanent when done.
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@immutable_infra · 3mo ago
Not if you countersink them slightly and skim over. They're about 40mm across and dished specifically so they sit below the surface. Two coats of finish plaster and you'd never find them again.
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@rueben_alsop · 3mo ago
There's a bedroom above so no loft access. Do the washers show through afterwards?
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