Ceiling Cracks On Lath And Plaster

18 Nov 2014
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United Kingdom

I have many cracks in my ceiling, mostly 5mm - 20mm wide on my ceiling. I am having the whole room skimmed, so would like to prepare the major cracks first.

There are two long cracks which follow underneath two of the joists. Holding a spirit level either side of the cracks shows that the plaster bows down very slightly towards the cracks.

Pushing the plaster near the cracks shows that it has detached slightly from the lath.

Here's a photo:


Should I follow a procedure which I've seen mentioned online where you drill holes in the plaster along the sides of the cracks, inject adhesive, and then screw in drywall screws with washers to try and re-attach the plaster to the lath?

Thanks for any advice.

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I would ask your plasterers advice as it's him who will be skimming it and have his reputation to protect.
My bet (I'm not a plasterer) is he will suggest overboarding and then skimming.

Good Luck
You cant even overboard that ceiling! the plaster has and is separating from the laths, the lot should be taken down and sheeted.

A skim will crack at best or could bring the lot down.
I agree with Alastair,, it doesn't look good. I'd take it down and put up 12.5 plasterboard, then tape and skim.
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Thanks for the replies. I should maybe have added that I have dug out all of the cracks to the state in which they are now, but I agree that it doesn't look good.

The other issue I have is that the ceiling has its original Victorian cornice. I'm not sure how easy it would be to bring the ceiling down without damaging it.

As long as the coving is sound the ceiling can be carefully cut a couple of inches back and sheeted up to it.

The pattern of the cracks on the ceiling suggests it has parted company with the laths and with the extra weight and moisture being added with another skim of plaster would in my opinion put the lot in danger of coming down.

Get your plaster to give it a proper check to make sure the pics aren't being deceiving.
If what is up there isn't too bumpy, then I would overboard , leaving a 250mm gap from the cornice. The edge of the board is fixed with an edging bead to give it a finish, and make a feature of the cornice instead of losing the definition of the ceiling member. Ie you end up witha 250 recessed band around the perimeter.

You could take any major loose spots and fill them with a layer of board or coat of bonding to receive the plasterboard.

The above is possible if there are no areas that will cause a bump in the plasterboard.ie you can screw the boards up tight.

If, as the lads say, your plasterer says take it down, the you can cut well away from the cornice to avoid damage to it, then cut a bit closer until you are about 250mm away. This is covered fully with 100mm Fibatape overlapped. Or better still, fibreglass rendering mesh cut to size, overlapping the joint by 100 mm and bedded in.

Key is get your quotes , see their work and pick the best quality tradesman.
His advice is then vital before you do any more prepping.
If the ceiling is sagging or can be easily pushed up then its possible that the joists are undersized & overspanned. Why not see if this is the case before doing anything else?

You can peer into the loft and measure the joist sections - dont go clambering about on the joists - note any stored materials. Has there been any activity in that loft since you've lived there?

If you come back here and say what you have found then we can help you further - it can be useless attempting remedial measures without finding the source of the damage.

Your cornice was run-in so there's a possibility of backing boards above it. Its great that you are concerned to keep it. Do you own a multi-tool or a cordless circular saw?
incidentally, old lime plaster on laths is often very thick and heavy. If you replace with 12.5mm board and skim, which will be lighter and thinner, then more noise will come through, you will notice the difference.

Yes, you can keep cornice, coving and other fancy features, in a Victorian or Edwardian house they were probably made in a factory and nailed up, so you can trim away the old plaster around them.

I would certainly pull down that old plaster rather than trying to rescue it. It will be dirtier and dustier than you could have believed possible. Empty the room first, put a doormat outside the door, tape up the door, take several bins and rubble bags, a broom and shovel, and a canister vacuum in there. Wear overalls and a dust mask and goggles, do not open the door again until you have swept up, vacuumed, and taken off your filthy hat and overalls.

I've learned much from your past posts but claiming that the Victorians nailed up factory lengths to that plaster lath ceiling would be wrong.

Bench, solid moulded "fancy" cornices ( eg leaves and fruit etc) were fixed in lengths. But that profile was run-in in-situ.

Either way the cornices were typically, well and truly fixed and, as you say, are good to "trim away ... around them."
how can you tell?

I have seen the tools used for running coving, but have only ever had houses with the nailed or screwed-up version.
FWIW: Experience of custom plastering, familiarity with what i was looking at. I hated that kind of work but got so that just by walking in to give a quote i could tell what i was dealing with, especially as much remedial dry rot work involved saving such cornices and working around them. If i got it wrong it could have been well expensive.

Unfortunately, i cant give you any detailed observations, so i hold my hands up for lack of that kind of evidence.

FWIW: I've run, repaired & pieced-in similar cornices in-situ. I've also run them on the bench and fixed lengths of them in place. I've also done solid mouldings on the bench and fixed them in place.

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