How thick lime plaster on laths?

[Zebra]

Silly quick question - on a ceiling, I'm going to put laths on battens between joists to plaster onto. I'm trying to work out how deep in to fix them - how thick will the finished plaster be? Is that a "how long is a piece of string" question?

 

[robgil]

Nope , there is a specific depth due to building regs or more specifically fire regs. I cant remember what it is though.

 

[tobydog]

Coincidentally I was reading an article this moring from Heritage Homes that I got from the Mike Wye website. It had a feature on sagging lath ceiling and said:

"The normal thickness of a lath and plaster ceiling is likely to be perhaps 30-35mm with the combined lath and lime or earth plaster. This is a lot of weight, perhaps 30-40kg per square metre."

It goes on to suggest ways in which to fix it.

 

[Zebra]

OK, thanks. An internet search has shown up a Building Regs document relating to fire rating for loft conversions which mentions a "30 minute standard" i.e. 12.5mm plasterboard with joints taped or 9.5mm plasterboard and skim or lath and plaster with 16mm plaster finish over laths.

Google also showed up a document from buildingconservation.com which reveals that "Published data on the fire resistance of lath and plaster ceilings is limited" and that "The testing that has been undertaken on lath and plaster ceilings has revealed wide variations in performance when tested under the standardised furnace conditions."

Dunno then. I'll take a guess and go well over 16mm!
Thanks guys

 

[lou]

On a related note, can anyone point me towards a previous thread about sound insulation between beams please? I can't trace it/ them.

The floorboards in two of our upstairs rooms form the ceiling of the lower rooms which previously had lath and plaster between them. That has come away and needs to be replaced, giving us the opportunity to put an additional insulating layer between the floorboards and the lath and plaster. I seem to remember that in the old days, record booths (anyone remember them?) where you went to listen to your record before buying, was lined with hardboard with holes in but I'm not sure if that was based on any technical understanding of sound reduction. Rockwool has also been offered as a suggestion and I also wondered about cork which also has heat insulating qualities.

Grateful for any ideas.

 

[MdB]

I put 60mm of rockwool designed for sound proofing between our floor beams. I can't say it made a noticeable difference.

 

[Zebra]

I'm no expert, but I think mineral wool is the standard thing for new build, but if your joists are shallower because of the ceiling being in between, you could try recycled rubber. I've used this on a floating floor before, to stop the timbers clattering on the concrete beneath, it's very dense so should be good for a small depth, but I don't know the specs. There are also more environmentally good products, sheeps wool I believe has good sound resistant qualities. Thermafleece is sold as being an acoustic barrier.
Googling "sound insulation floors" comes up with lots of products.

 

[Zebra]

On the thinkness of lime plaster, the Old House Store gave me an answer: 9mm base coat, 9mm second coat, 3mm top coat, and that meets fire regs.....

 

[middi]

.......and ear plugs for sound insulation ( it's very cheap !!!! :wink: )

Middi

 

[Zebra]

Yes, lots and lots of ear plugs stuffed into the gap between the joists. That outta do it