Hello,
I wonder if someone could help me. I'd like to render a couple of interior walls with a lime/sand mix. The walls have old plaster on them which is very tedious to scrape off. Is it necessary? Does it matter if some is left on the wall? I've got a feeling I heard somewhere that gyps and lime are not really compatable.
Thanks for any advice.
Why are you using lime? It'll be OK over gypsum as long as the wall is dry. The problems come patch-plastering lime mortar with gypsum.
only need remove what isnt sound
NT
Was the building originally plastered with lime and has since had gypsum plaster patches?
The gypsum patches in my house didn't key terribly well to the lime, belted it a few times with a hammer and it came away in slabs. New lime then keyed beautifuly to the old lime.
If the gypsum is sound, I'd think about roughening the surface to improve key, but otherwise to leave it.
It's normally perfectly OK for a day or two!
In my case the gypsum plaster being self-detaching was very pleasing to me - I didn't put it in, and I wanted shot of it.
I'm using lime because I prefer it, and anyway if I tried to do any plastering I'm sure I'd only make a mess of it. I've a lot of respect for plasterers!
I'm surprised that you say the wall needs to be dry, I was thinking that I would need to wet the wall as plaster is so porous.
Thanks to all, Alistair.
So long as the substrate is sound (very important) then key it up enthusiastically, damp it down well (cos it will be bone dry), paint over with limewash (ye traditional PVA) and start plastering
Anna
~~ Anna Kettle, Suffolk, England |""""| ~ Lime plaster repair and conservation / ^^ \ // Freehand modelling in lime: overmantels, pargeting etc |____|
I meant that the wall should be normally dry, i.e. not a generally damp one.
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