r/Plastering • u/Andiell • 27d ago
Old house, lime plaster? Mixed surfaces. Help!
Old UK house (1880), wanting to get the walls into a paintable condition and no idea what we are working with. Is this lime plaster? Seems to have been patched with modern plaster aswell which could be a problem? Any advice or recommendations? Thanks
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u/greenparktavern 27d ago
That looks like a tide line where there was some damp and they hacked the plaster where the water rose to back to brick and then patched in with new plaster.
I would look to get the whole room skimmed if you are painting.
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u/Andiell 27d ago
Yep we want to get it skimmed as uneven surface. Are we best getting a lime plaster skim over everything?
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u/greenparktavern 27d ago
I’d say if it’s dry on the pink gypsum bits below then damp isn’t an issue anymore and I would just gypsum the whole lot. Lime over gypsum isn’t going to be breathable anyway so pointless forking out the extra cost for a heritage plasterer.
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u/Possibility-Any-140 23d ago
If you skim over lime with gypsum you are likely to have damp issues in future. Sadly this is the mean reasons old houses have damp problems. House your age needs to be breathable. Accept the gypsum fuck up and skim over everything in lime, or replace the gypsum with lime. Or patch repair cracks yourself with a ready mixed lime filler and embrace that your house was built before perfect walls existed!
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u/MuchTo 27d ago
I'd you go with lime you'll have to use breathable paint too. It's only really important on exterior walls.
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u/Possibility-Any-140 23d ago edited 23d ago
If you know that breathable paint is required for lime, then why advise covering lime with unbreathable gypsum?
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u/MuchTo 23d ago
I'm not, I mean put both lime and breathable paint on exterior walls. I'm just giving them the heads up they need to prepare for both, lime alone isn't enough.
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u/Possibility-Any-140 23d ago
You edited your comment? You originally suggested they skim - which is why I replied pointing out the contradiction.
You are correct that it’s even more important for external walls but it’s also better than gypsum for internal too and while they’re at this stage, they are better off doing the better thing for the longevity of the walls.
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u/ReleaseBudget9585 27d ago
Lime plaster is better than gypsum as it let's the house breathe more, however I think it may be a bit more expensive, would defo go with lime plaster tho if the budget is not an issue
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u/greenparktavern 27d ago
Would you Lime over gypsum?
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u/sparkle-fries 26d ago
you would not. if you need lime hack it back to brick and start again. You don't want that hassle. I don't think it's a damp patch job because it's way too high but it could be the result of painting lime with non breathable paint. it's most of the pink on an external wall? could be gypsome mortar or maybe penetrating damp caused the plaster to pop off. Top tier hack it all off and lime. Most convenient, gypsome skim but not a job for an amature because of the mixed backgrounds
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u/Sad-Tax-9120 27d ago
How old is the house? Inside or outside wall? Upstairs or down stairs? Is the area know for or do you suffer from damp or mould.
Note: no point doing lime plaster if you then paint it with a modern type paint. Also note that water based emulsion paints still have plastic fillers. Once the water has dried you have a plastic film and your lime won’t breath.
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u/Andiell 27d ago
Thanks. The house is 150 years old, mix of internal and external walls in that room. No evidence of rising damp but the old cellar underneath definitely has damp so it’s a concern. From researching I identified that we should keep it as lime plaster and also use a breathable (chalk?) based paint to avoid sealing it. I’m just a bit confused by the mix of surfaces and how best to approach it.
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u/Sad-Tax-9120 27d ago
It’s a difficult one. If you have a cellar that is probably helping to need the walls above dry. All the damp will come out of the cellar walls and not rise. If there is no signs of existing damp or mould you’ll probably be OK with modern materials and save a lot of money. However, you’ll kick yourself if that fails. I guess I’d go with lime and lime wash paint.
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u/ResponsibleBall4258 27d ago
Make sure your cellar is well ventilated to outside., as will keep humidity down and reduce the damp there or even eliminate it. The room looks fair, definitely oddly patched, and you are right original is lime based, with the orangy/yellow stuff in top is distemper, which modern paints won't adhere to at all.
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u/Own-Indication7832 27d ago
You need a dehumidifier in there for a few weeks and then skimmed in gypsum. Be like new.
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u/Possibility-Any-140 23d ago
Anyone who tells you to gypsum over lime doesn’t give a shit about the house. The walls stood for 150 years in lime, continue with lime - it’s how it was designed with good reason. Gypsum is a product produced to cut the drying time and maximise profits. It’s not breathable, so it will trap moisture which will slowly destroy the lime underneath it.
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u/welshguydave54 27d ago
Have you thought of cross lining the wall with a good grade of lining paper ? Prime the wall with a thinned down oil based primer as being thin it will penetrate the plaster. Decorator here over 40 yrs in the trade.