Plastering of lime based walls

kevinhughes wrote: »

Hi all,

Has anyone had any experience with applying a skim coat of gypsum plaster over lime (lath & plaster walls)? Reason I ask, our walls need re-plastered as they are in a bad state. I have done some research and majority seem to suggest not to place modern gypsum over lime based walls, as lime needs to breathe? I am unsure on the best approach, both plasterer’s we had to quote said modern gypsum would be fine, think they apply PVA glue and soak the walls before applying the skim coat of plaster. Any advice greatly appreciated.

What type of house do you have? (ie red brick? oak frame white pannel etc etc and age please - then I can help

kevinhughes wrote: »

Hi there,

House is Victorian built around 1870, made of sanstone.

Cheers

Ok, yes internal partition lath and plaster walls - you can skim modern gypsum onto them no problem. Be aware though that the finish will not look as "soft" as the original lime/horsehair. When people talk about lime "breathing" what they mean is that it has self healing propeties, that is to say that when the building "moves" the lime will "move" with it and cracks will self heal - this is more for external walls though to be honest what happens (with the case of your sandstone house) is moisture is allowed in through the lime pointing (which is lime) between your sandstone walls but then also let the moisture evaporate in the same manner - preventing the decay of the sandstone itself. If you decided to point your walls exterior with sand/cement your sandstone will deteriorate quite quickly and the "hard" cement pointing will stay as strong as ever.

Plasterer wrote: »

i'll get a diagramme to show you what i mean - 10 mins

Below the picture from one of my books should explain a little clearer
As the walls you require plastering are internal "lath" then they are not open to the elements (moisture) which is why using modern gypsum on them is fine