Replacing damaged lathe and lime ceiling?

[Pogonation]

Hi I just joined this forum although have been reading threads for some time.

I wondered if I could get some advice. I have a converted apartment in a house built in 1874. The stand out room in my apartment is a large 40sqm living room with 12ft ceilings and a nice big bay window.

Unfortunately due to a leak from the apartment above >50% of my ceiling was flooded. The lining paper has been removed and revealed a wet (after 3 weeks drying), bowed and cracked ceiling. The lime has delaminated from the lathe and there is a good 1.5inch or so movement when pressing up and down. Other areas in the room are also found to have delaminated. Luckily my insurance will be covering the job.



Here is a photo although it doesn’t look too bad the plaster has separated from the lathe.

I have spoken to a heritage plasterer who has advised cutting up to the level of the cornicing and removing the ceiling. He would take a mould of the decorative strip (inset from the cornicing) and replace that. He would plasterboard the entire area to the same level as the cornicing and plaster it so it blended in with the cornicing.

I figured losing such a dense material may increase the risk of noise transmission so thought that it would be a good opportunity to insert acoustic rock wool between the joists and also use denser acoustic plasterboard in 2 layers with green glue inbetween.

I wondered what peoples thoughts are on this method of repair? Would it be suitable, or should I be looking for an alternative solution? Do you think the sound insulation methods above should leave me in the same/better situation when it comes to sound transmission from the flat above?

Thanks I’m advance for any help!

 

[Socksitis]

Anyone can replace a lathe and plaster ceiling with plaster board, but you have a lathe and plaster ceiling!
I would have thought, remove the plaster, lathes may well be fine, then lime plaster again - skilled job, but you do have a beautiful ceiling - well did have.

 

[malcolm]

I repaired mine my knocking off any just the areas of plaster that have detached from the latch and re-plastering them in lime. Lath should still be fine. Filling and putting the lining paper back on will sort out any small cracks.

Removing the whole ceiling will end up making it a big job and it would be shame to remove a nice ceiling like that.

 

[Lacan07]

Hello,

I guess if the insurers weren't bound to cover the costs your decision might depend on how much of the ceiling is affected (looks about half from your photo) and how much you care about the flat. As others here have already stated the lathe is probably fine and a skilled heritage plasterer can simply remove the damaged plaster ad reapply. Even I've repaired patches of my ceiling in this way.

Keeping the lathe in tact might also ally your fears about increased noise. I've no evidence to back this up but i"m also of the opinion that good a thick lathe & plaster ceiling is probably way more sound resistant than 9mm or 11mm plasterboard. Even though it isn't affectively 'decoupled' from the joists just think about the fact they'll be hundreds of slats of lathe individually spread across the timbers. If you do decide to remove the ceiling I would definitely think about decoupling the new ceiling from the joists as well as insulating between the joists. Decoupling will reduce 'impact' noise (footfall). Insulating between the joists will reduce airborne noise.

 

[RBailey]

I guess if the insurers weren't bound to cover the costs your decision

It should be the apartment above's insurance (or the buildings as some lease holds have a common policy), you should be covered for a "like for like" repair, ie. keeping the lathes.

I am intrigued / questioning as to why a true "heritage" plasterer recommended plasterboard, I'd be looking for a second opinion from different plasterer.

 

[Pogonation]

Thanks everyone for the replies. It seems the general consensus would be to replace with lime as per the original ceiling.

What would be the main benefits of doing so? With the paper over the existing lime there is not really much character visible and it looks very similar to a modern ceiling to me (see photo below)



If it were boarded I suppose benefits would be that I could soundproof and also it would dry significantly faster. One of the things I’m worrying about with lime is that it would be months before I could redecorate my ceiling?

What are the main reasons to stick with existing lime?

Thanks

 

[Pogonation]

It should be the apartment above's insurance (or the buildings as some lease holds have a common policy), you should be covered for a "like for like" repair, ie. keeping the lathes.

I am intrigued / questioning as to why a true "heritage" plasterer recommended plasterboard, I'd be looking for a second opinion from different plasterer.

It is insured by the freehold insurance (of which I am a part owner) and I suspect they should cover like for like if I request it.

I am not sure why the plasterer recommended it. He said since multiple areas are delaminated across the whole ceiling, doing thick plasterboard across the whole ceiling would last for 100+ years and once blended with the cornicing would basically look the same. I guess it is probably a faster job too although I am not sure about this.

 

[Pogonation]

Spoke to heritage plasterer again and he said gold standard in my property would be to re-lime plaster as per before. Was trying to save me costs but as I said insurance is at a premium for an old building so should be like for like. Thanks for your input everyone. Will be nice to have a new ceiling sorted soon!

 

[Cubist]

What would be the main benefits of doing so? With the paper over the existing lime there is not really much character visible and it looks very similar to a modern ceiling to me (see photo below)

The main benefit is the quality of the bond between the new and old plasters. Gypsum and lime based products don't form good chemical bonds and getting clean uniform seams at the boundaries between them can be problematic.

I'm intrigued by the fact that there are significant bulges in the ceiling as the lath is, in effect, a wooden skeletal structure pinned to the underside of the joists. A base, or bedding, layer of plaster will have been pushed onto and through gaps left between the laths to provide the basic structural strength of the ceiling. A thin skim coat of plaster would then be applied to produce the final flat/smooth surface. Is there any evidence that the laths have been separated from the joists?

 

[Pogonation]

The main benefit is the quality of the bond between the new and old plasters. Gypsum and lime based products don't form good chemical bonds and getting clean uniform seams at the boundaries between them can be problematic.

I'm intrigued by the fact that there are significant bulges in the ceiling as the lath is, in effect, a wooden skeletal structure pinned to the underside of the joists. A base, or bedding, layer of plaster will have been pushed onto and through gaps left between the laths to provide the basic structural strength of the ceiling. A thin skim coat of plaster would then be applied to produce the final flat/smooth surface. Is there any evidence that the laths have been separated from the joists?

That makes sense thanks for explaining. I was a bit worried that this could be the case and I would end up with cracks where the gypsum and board joined the cornicing which was left in situ so it seems you have confirmed one of my fears.

I don’t believe the lathe has detached from the ceiling but rather the lime has separated from the lathe. Presumably the weight of the water (it was building up and raining through cracks and coming out of the hole where my light fitting was) caused the lime plaster keys (as per diagram) to snap off and allow the layer of lime to then sag down and crack below the level of the lathe. Now held on by a few keys either side of the areas which are sagging and have detached themselves from the keys.

Difficult to know however as I cannot see above the level of the plaster.

 

[Feltwell]

One distinct advantage of lime is it is much more tolerant of any future minor leaks than plasterboard. A leak above plasterboard pretty much always trashes it, it just turns to mush. Lath & plaster normally survives OK - though it has it's limits, as you've found. I've had a couple of leaks here and it's been fine, has dried out in a couple of weeks, just leaves a stain that requires redecoration.

I'm presuming access from above is not possible - otherwise one repair method is to prop the ceiling underneath with props & boards, then pour plaster of paris from above to re-bond the plaster to the laths. Only works of course if the laths are all still securely attached to the joists, plus yours may well be too large an area for that to be a practical option.

 

[Cubist]

If the base coat has parted company from the laths it would be relatively easy to remove the damaged plaster without pulling down the laths. A competent/skilled plasterer could, assuming that the exposed laths are in good condition and securely attached to the joists, then easily replace the base and skim coats.

However, given the amount of vertical movement you are seeing, and the fact that sections of plaster have not fallen away to expose the underlying laths, I suspect that some of the nails used to pin the laths to the joists have failed or simply pulled out. That said, the repair need not include ripping out the plaster over and extensive area. Very probably you could also avoid introducing plaster-board.

 

[Pogonation]

Still haven’t got this issue sorted yet. Long delays and a cancellation. My new plasterer is suggesting hemp board (or wood wool board if can’t get it) with like plaster over the top. One benefit of this is that I can insulate the ceiling above. Just wondered if anyone has any experience using this method?

Also I did have a plan to use vinyl (Tecsound) sheet then 19mm acoustic plasterboard but new plasterer said not ideal to use gypsum as could cause rot to joists over a long time. (Joists in ceiling run horizontal compared to exterior facing wall so no air brick). Would people tend to agree with this?

 

[Cubist]

I cannot claim any experience of using hemp or wood wool boards but know that many of the contributors here have and will soon offer their opinions concerning it.

Your new plasterers comments though are rather intriguing as I am unaware of any way in which gypsum may induce rot in timbers. I stand to be corrected but my BS meter is buzzing. Also, while the use of air-bricks above the ground floor is not unknown, particularly in multi-floor apartment blocks, they are not commonly seen in houses except in the upper sections of an exterior wall and below the ceiling.

 

[Feltwell]

I'm with Cubist - breathability doesn't matter on ceilings, just like it doesn't matter on internal walls.

Wood wool boards - ask "Zebra" on here, I think most of the interior of her timber-frame house was done with wood wool boards prior to being lime plastered over, *if* memory serves me rightly.

 

[Lacan07]

I think there's different levels of importance with regard to breathability within certain areas of the house, for example breathability is paramount in a ground floor wall. The main purpose of an old house however was / is to allow moisture to pass through the fabric of the building, so technically that includes all walls and ceilings, but as we know that's the ideal scenario and everything is a compromise. I don't see why the builder believes a gypsum ceiling will produce rotting joists, a greater chance of condensation perhaps at a push.

Aren't wood wool boards the (Eco) breathable equivalent of plasterboard?

 

[Pogonation]

Thanks for the replies! If breathability isn’t an issue (and presumably the space can breath through the timber floor above anyway) then I would be now a bit more inclined to do the the tecsound (vinyl roll/tiles) with acoustic plasterboard and acoustic mineral wool. The benefit being I can just get it done and decorated and move my furniture back in (it’s a 1 bedroom flat and I’m currently living in a bedroom and kitchen) and be done.

Do you think the vinyl would cause an issue with damp since it is impermeable as opposed to gypsum plasterboard (only) that still breathes a little bit? The main reason I’m doing this is because I need the additional mass to prevent noise from above without lowering the ceiling (I’m keeping the original cornicing).

 

[noj]

I can't see the point of the vinyl?

Regarding acoustics, a relatively hard slab of plasterboard can act as a good way of transmitting sound, anything with a greater variation of texture/density will deaden it. Woodwool plus a fibre or hemp reinforced plaster skim should be much more effective...

 

[Pogonation]

I was under the impression that the best way to prevent transmission of sound is mass (among other things such as the acoustic mineral wool)?

The tecsound adds an additional 7kg/m2 of mass for a 3.5mm layer. It also has additional damping qualities similar to that of green glue. Then an additional 15kg/m2 from a 19mm acoustic plasterboard. This will give total mass of 23kg/m2 approx with the skim. (Original lime and lathe ceiling I calculated as 27kg/m2)

I only have 25mm to use to match up with the original cornicing so I can’t go silly. I did a calculation for wood wool board and hemp lime skim and that worked out as approx 12kg/m2.

This is pretty important to me as I have a flat directly above me with permanent residents.

 

[a twig]

Depends what sound you are trying to reduce.

If you want to minimise the footsteps from above then filling the void with insulation and then constructing a damper / isolated acoustic plasterboard ceiling would be your best bet imo.