When did lime plaster stop being used?

[cconnor]

Hi, im restoring a beutifull lodge built circa 1920 - the walls and ceilings need attention due to cracks and years of poor wallpaper removal techniques.

Can i assume that i need to reskim the surfaces in lime plaster? When did this material stop being in general use?

What happens if i use modern gypsum plaster?

Thanks

Chris

 

[Gervase]

Depends where you are - in some places lime plaster has never stopped.
It's quite possible that your place was done with lime plaster, and it's certainly a good choice for renovation because it accommodates far more movement than gypsum plaster.
The downside - and the reason it fell from favour with yer average builder - is that it takes a bit longer to plaster with lime than gypsum. And, to be honest, probably 85 per cent of modern work that gets called 'plastering' is in fact just skimming; floating a 2-3mm coat of pink hard stuff over plasterboard. Done well, it looks good, but it ain't plastering!
None of which has really answered your question, I know. If you use gypsum...well, in a perfect world, nothing happens, and everything is fine. But, if the original plaster is lime, then a gypsum skim will just put a hard crust over the top and will probably crack in time.

 

[BMcD]

Although gypsum plaster has been around for thousands of years and was used on the pyramids and was being used in this country in the 1600s it was not used in the way modern pre mixed gypsum plaster is today, it wasn't until the 2nd world war that that modern plastering techniques started to be widely used.In 1920 they would almost certainly have used lime based plasters for internal works though they may well have gauged it with gypsum to improve its setting time and so long as it's sound and not been painted then there should be no reason why you can't re-skim with lime. Take note however of external corners and reveals which may have been formed using a gypsum cement such as Keenes cement, these set much harder than lime (or regular gypsum plaster) and are used where damage may easily occur. In which case you can cut back the existing lime skim in a 3"-4" band from where it butts up to the cement so as the surface of the lime backing coat is a few mm below the surface of the cement leaving room for the new skim to finish flush. On the other hand there may be wooden staff beads which you may want to cut back from so as the new skim dosen't over ride the bead.
If you skim over lime with gypsum then as Gervase suggests it will probably crack rather like icing on a cake where a hard brittle surface has been applied to a soft yielding background.

 

[NT]

The first known mortar, back in something BC, was a mixture of earth & gypsum.


NT

 

[biffvernon]

A letter from Stan Wild, Shropshire, in last week's New Scientist (27 Jan) describes a hut in Serbia with a concrete floor dated at 5600BC.

 

[NT]

Do you know what the concrete was made of?

NT

 

[andrew gayton]

probably lime/earth/ash/stone