Replacing plaster ceiling

[Catarina]

The ceilings of our 1880's Edinburgh tenement are badly cracked because we are converting the loft space and there have been people walking around upstairs on the joists. The plaster has lost its key over large areas, and is sagging. The ceilings have collapsed entirely in two small rooms in the flat below us (not our fault! - dry, simply collapsed due to age) and we're pretty convinced ours are going to go soon.

We plan to remove the plaster ceiling and replace with drywall, but here is a ceiling light rose and perimeter cornicing which we want to preserve. Where can we find detailed instructions on how to do this ourselves? How is the ceiling rose attached to the joists? How can we secure it if we remove the rest of the flat ceiling? We aren't too keen on replacing the plaster, but might. My husband has successfully plastered walls in the house, but would prefer to drywall and then put up a skim coat.

We have no budget, it's a small flat, and there are two children, so simply moving the books and furniture out of the room to be re-ceilinged is a headache enough (with the loft conversion happening at the same time), without embarking on a major conservation project, but we aren't prepared to lose the rose and cornicing, either.

Many thanks in advance for any advice or links!

Catarina

 

[Lime]

The ceiling rose and cornice are an integral part of the plaster.
It is not screwed up or glued like modern plaster fittings.
The plasterers who put the ceiling up used a mould with plaster directly on the ceiling to make both the rose and cornice.

If you are converting the loft space you will need to reinforce the joists as most lofts were not designed to be inhabited.
You may need planning permission to alter the loft.
Building regulations and fire regulations need to be complied with too.
Councils can force you to remove your work if you have not complied with the regulations.
There is no time limit exemption.

Most old ceilings fall down due to damage.
Dry ceilings are good ceilings.
Weak and slender joists can cause a ceiling to fall because movement cracks the ceiling below.
Also I have known people who have "tidied up" under the floor boards removing all the plaster keys poking through the laths.
The plaster keys hold up the ceiling below!

 

[worms]

Catarina,

The whole process sounds intriguing!

In a tenement is the loft space not owned (and the responsibility shared) by all the flats in the close? If you take on a more intimate relationship with the roofspace does it follow that you take on sole responsibility for all the future roof repairs as well? Are your neighbours and the factors fully on board?

I assume that the building is not listed.

 

[MdB]

I am very much not an expert on this but others in the past have said that plaster + lath ceiling can often be repaired. It keeps the historical fabric and might be an easier solution too.

 

[Nigel]

I have observed similar repairs to various late 19th century tenements in Glasgow. What the builders have done is retain the cornice and rose and removed all other plaster, leaving the laths in situ. They then infill, blending the new plaster and the cornice/rose. I can't offer up what plaster they have used etc as I have just been nosey, looking through windows of development properties. However, it does indicate it can be done, unless your cornice/rose themselves are fatally damaged.

 

[Penners]

I reckon the only way to achieve what you want is to carefully remove and patch the loose bits of plaster that have completely lost their key.

As has already been observed, it's extremely unlikely that you'll be able to remove the laths without also removing or at least badly damaging the plaster mouldings. And you can't screw up plasterboard on top of the laths because of the mouldings you need to keep.

In your shoes, I would remove all the unrecoverable areas of plaster from the laths, then set about ensuring that the laths are securely fixed to the joists - use screws and washers if necessary. Once the laths are firmly refixed, then you can apply patches of lime plaster.

 

[chuckey]

The cornice could be moulded in-situ, but I would have thought that the rose would have been a patent moulding screwed on, I say this because as the weight of the rose is substantial, it would have been the first bit to fall off if the backing coat is breaking off the laths or the nails are rusting through.
Frank

 

[Catarina]

Many thanks for all the advice and suggestions. We are still very puzzled as to how that ceiling rose is attached and how we can save it.

In response to questions, we do have planning permission, a building warrant, and legal right to the space (I know this sounds too good to be true, but legally, the position seems to be that the roof is common and the loft space is the property of the top flat. We will take on more responsibility for the roof now that we have put windows into it.) The joists are being reinforced and there is other structural work being done. We can think of no other reason for the ceiling suddenly cracking up and losing its key than the traffic it is receiving from builders and ourselves walking around on the joists upstairs.

If we were to try and do patch repairs, would we need to use lime plaster for practical resons, or just heritage ones? Would a modern gypsum plaster (have I got that right?) not bond properly or something? It seems to me we have repaired the walls with modern plaster.

Catarina

 

[Penners]

If we were to try and do patch repairs, would we need to use lime plaster for practical reasons, or just heritage ones? Would a modern gypsum plaster (have I got that right?) not bond properly or something? It seems to me we have repaired the walls with modern plaster.

I'm not talking from first-hand experience, but quoting what I've read from the experts on this forum, lime plaster apparently has an element of "self-healing" that gypsum doesn't possess. So, assuming your existing ceiling is lime plaster (which seems likely) you should get a much more visually satisfactory patch with lime than with gypsum.

Hopefully, one of the lime experts will confirm or deny that suggestion.

 

[worms]

the loft space is the property of the top flat

That's interesting.

Its good to know there is some reward for you having to trek up all these stairs to your front door!

 

[MdB]

I'm not talking from first-hand experience, but quoting what I've read from the experts on this forum, lime plaster apparently has an element of "self-healing" that gypsum doesn't possess. So, assuming your existing ceiling is lime plaster (which seems likely) you should get a much more visually satisfactory patch with lime than with gypsum.

I'm certainly not an expert and I think Penners knows more than I, but I thought the self healing property of lime was when it was under pressure as a mortar in a wall.

 

[Penners]

I think Penners knows more than I

Good grief - no!

As I said above, I was simply repeating something that I've read on this forum.

 

[Ian Bond]

Gypsum plaster has been used in the past for lath and plaster walls / ceilings.

Trouble is, it is rather hard and brittle, so tends to crack where there's slight movement in the building.

Mind you so, does lime plaster, but it is a bit more forgiving. As for self healing - perhaps lime plaster does at some microscopic level, but to all practical intents and purposes, I think it's wishful thinking. I wish my house would heal itself.

Where I have repaired lath and plaster, areas patched with gypsum have been a pig to do. Where lime plaster detaches and fails, you can easily remove it from the laths, use washers to secure the perimeter if necessary and apply new lime plaster to the laths. Getting the gypsum off the laths without breaking them is not so easy.

To be honest, I can well understand if most people prefer to go the easier route and either over-board the ceiling with plasterboard, or use a plasterboard patch and skim over the repair.

 

[Ian Bond]

.... Next door neighbours are having work done, and as a result cracks have appeared in my newly repaired lath and plaster ceiling.

The ceiling joists overlap in the party wall, and there's been some extremely heaving hammering and drilling in the affected area. I expect it would be much worse with gyspum plaster on lath. Maybe even gypsum skimmed over plasterboard would have cracked too in those circumstances.

 

[MdB]

The example I saw for lime repairing itself was on TV quite a while back (no idea which program). They showed a brick + lime mortar wall which didn't have any foundations. In one corner there had been subsidence and one section had dropped. If the wall had been made using cement, there would have just been a large crack. Here, the lime had given way allowing the movement but had continued to keep mortar all around the bricks. They showed one of the bricks which had been rotated by over 90° but still doing its job. A structural guy had been called in to look at it and he was happy to leave it as is. I think the wall was in the middle of a terrace so would have been contained on most sides which would have helped.

(My memory on the above may not be perfect, it was a while ago.)

 

[Ian Bond]

If you read through the document you'll see a guide to the repair and conservation of historic plaster.

http://www.mendip.gov.uk/Documents/Regeneration/Heritage Conservation/Heritage Matters/Iss10.pdf

You need to avoid walking around too much in the room above a newly lime plastered ceiling for several months to allow it to reach sufficient strength, otherwise it will crack.

My house is unlisted, but I've spent an inordinate amount of time and effort (not to say money) restoring things properly. Result - 10 years on one room finished and the rest still a building site!

I have no budget myself either now, and to be frank I don't think it's worth bothering spending the time and money on something that someone else will either just rip out or plaster-board over anyway, because its a bit wobbly.

There are plenty of what I'd consider to be DIY bodge-it guides on t'internet for cheaper/quicker repairs:

http://www.guardian.co.uk/lifeandstyle/2008/mar/01/diy.homes9

I'd get the ceiling propped if it's badly sagging - there's an incredible weight of material and a potentially nasty accident if it does fail.

What's the builder got to say about the damage / dangerous ceiling?

 

[Gervase]

Walls do self-heal to an extent, but the process does work better under compression and in high humidity. In a ceiling, sadly, there ain't either of those. That said, a well-haired plaster will flex to an astonishing degree before cracking, and can thus accommodate a lot more stress and strain than gypsum, and is always the best course to take.

 

[Ian Bond]

You're right Gervase - it's a real shame that the historic ceiling was damaged during the work.

It may be repairable, I hope so.

I'd still ask the builders for some help, as they need to make sure that the building is kept in a safe condition especially as you are living in it.

Not sure what sort of grounds you'd have for insurance claims, or even asking the builder to contribute to the repair bill - is there proof that the ceiling was in good condition before the work started?

Plus, to be fair to the builder, some damage is inevitable if major works are carried out on a structure (within reason). Unless they've been particularly careless.

 

[Catarina]

Well, as predicted, the ceiling came in - a 6' by 4' chunk fell down while joiner was working upstairs. NO one was hurt. Rest of plaster has now been taken down by my husband and a friend. Flat is as bad as can be imagined, dust everywhere. It's nobody's fault - we noticed the cracks appearing as soon as people started to walk around up in the loft to take measurements and so on. It may be that if plaster ceilings are subjected to regular movement, they get a bit of flexibility, but no--one had walked around on top of this one for 130 years. Plus there was no flooring and they were walking straight on the joists.

The good news is that the cornicing and ceiling rose are secure, rose seems to be bolted up there somehow.

Bad news is that there is no place for a Christmas tree!

 

[Moo]

Bad news is that there is no place for a Christmas tree!

Oh, I dunno - surely that ceiling collapse will have given you some much-needed extra headroom.