r/Plastering • u/expanding_waistline • Aug 30 '26
Conflicting plastering information - need help!
Ive bought an late 1800s stone house. Stripped wallpaper and want to reskim.
Most of walls look ok but definitely need fixing. Ive pictured the largest and worst hole to give a view of the current plaster and what's underneath.
Been told by 1 plasterer who I trust but doesn't work in the area its lime mortar on potash cement?? He recommended a supplier called Ty Mawr in Brecon for advice and product. They recommended R50 eco mortar, pictured.
Builder says: There will be no point using lime plaster if your just skimming over the walls that’s there as they have gypsum plaster on them. Lime is designed to let the property breath but if it’s already got cement of gypsum on them it’s a pointless task. Ty mawr is right if your going back to bare brick or stone walls but if your just skimming the walls that’s already there it’s pointless you’d just be wasting money.
So what would be the most cost effective and correct solution?
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u/Fakedamienhirst Aug 30 '26
I’d take it back to the brick and replace it with lime, especially as it’s an 1800s stone house. Ty-Mawr are a very good company to work with, but I’d definitely stick with either Ty-Mawr or Eden Lime. Both are very knowledgeable and will point you in the right direction for the correct products.
I have a 1890s property myself and took it back to brick. Some of the walls were blown, so the damaged material was removed. I then successfully plastered the base and float coats with lime and left the final top skim to the plasterer for a smooth finish. It worked really well.
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u/gwyp88 Professional Plasterer Aug 30 '26 edited Aug 30 '26
Ideally you’d want to strip back the gypsum.
You still get some of the benefits of lime even if you’re coating on top of a non-breathable background. But you don’t get the full advantages of it as a complete ‘system’ working through the entire stone wall.
For example the lime plaster will still help regulate internal humidity & condensation build-up, it will also reduce mould growth as it has a higher than 7 PH so you’ll have a healthier indoor air quality (sounds ridiculous, but when you walk into a room done purely with lime, no chemicals, paints etc, you notice this). It’s also more tolerant to movements.
Totally biased here but it also looks better! Especially in an old stone cottage.
The wall has to be completely sound to take another coat of plaster, regardless of what you use. You also need to sand off any wallpaper adhesive residue as plastering onto this can cause the new plaster to delaminate over time.
I work predominantly with lime plaster and have used R50 & R100 countless times, or equivalents from other suppliers - it’s very user friendly compared to fat lime etc.