How to identify lime plaster ??

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I have a top floor flat in a regency town house.
The house was converted into flats many years ago and therefore may have been replastered since originally built.

The plaster in my flat is white on the surface and the plaster underneath is very dark grey. It's applied to laths.

Is this lime plaster? If not, what are likely ingredients

I've heard of Lime plaster

I've heard of Gypsum plaster

Is there any other kind it could be?

Could it be cement based underneath with a lime top coat?

Say it was done in the 1940's; what did they use then?

Apologies for profuse questions

What could the othert possibilioti
Is the white plaster very flat and smooth like modern finish , grey plaster was around ten or more years ago , could be bonding that is grey in colour..
Best to ask the next plasterer on site, why do you need to know, are you intending to skim over it.?

The plasterer said he could skim over it (prob using the pink stuff) . He says the ceiling is very sound. there are some cracks but they can be filled.

This ceiling had distemper on it which has had a scrub or 3.

As grade 2 listed building i don't think pink gypsum skim is appropriate.

I am worried about the effect of pink gypsum on ceiling of old building(the attic is above ) in conjunction with the distemper and goodness knows what else it on this ceiling.

If the paint flakes off that isn't so much a problem as if the plaster pops off.

I think i am going to fill the pits myself piecemeal and go for an 'aged' look
I few mm of gypsum based plaster is unlikely to cause you any problems. However, you wouldn't be able to simply overskim the ceiling and cover the cracks because given time, they will simply reappear. In addition, raking out the cracks and filling is unlikely to solve your problems.

If you're going for an aged look, why don't you just leave the cracks as they are? :)
My house is a Georgian house too and grade 2 listed.
As I am doing each room, if the walls (which are lime plaster) are sound then I just put PVA over them and skim with multi finish. It is a good result and with no problems. However, for the external walls I am completing them in lime so as to not cause any damp problems.
The ceilings are all being boarded straight over and skimmed. I would not recommend skimming over an old lath and plaster ceiling that is cracked. As Minh says, they will only reappear later. Hope this helps.
A badly cracked ceiling that is solid can be skimmed if you put on a coat of skim and trowel k rend mesh over the whole ceiling, it will hold as long as any other method.
just came across this post it is more than likely just a lime plaster mix the reason why you might be thinking that it has a cement background is the finish coat is white in colour as lime putty and fine sand will have been mixed probably 1:1 but obviously the background will be darker as it has a stronger mix hope this helps and I personally would go back to the original as it will let your building breathes whilst gypsum would cause dampness
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