Lime plaster underneath woodchip wallpaper: should I be worried?

[a twig]

Controversially (as many seem to insist on only fat lime inside) a quick 2mm thick skim with an NHL based plaster is pretty DIYable - goes off quicker, and using a fine enough sand any mistakes can be tidied with a scraper / sandpaper

I’ve also found that if you buy it premixed so all you have to do is add water then many “non-heritage” plasterers are keen to have a go, I got a few rooms done that way at a fraction of the cost of “heritage plasterers”

 

[Feltwell]

Did you use a bonding agent to the old plaster Twig?

 

[malcolm]

I find it lovely when I can strip off lining paper with layers of wallpaper and paints and get back to the original lime surface. It means I don't need to do much work. But there are 2 options from there.

The common modern approach is to skim with gypsum and paint with emulsion paint. It looks good for a few years but within 30 years people will have painted several more coats on. There will be problems with the build up of paint being too thick and with emulsion paint not being breathable. The finish will fail, maybe you'll get damp. You can't get back to the original plaster. The house will get into a cycle of having to go back to brickwork every 30 years.

In the past they used lining paper on top of lime plaster. They used wallpaper or breathable paints on top. You can paint or paper on top of the lining paper and when the build up gets too thick you can strip it all back to lime and start again. This is my approach.

I find it mad that my windows are 100 years old (oldest one is 190 years) but the new build next door needs new windows after 9 years. It's the same with lime plaster. It could be perfectly good for another 100 years. Or you could decide to ruin it.

 

[Lacan07]

Controversially (as many seem to insist on only fat lime inside) a quick 2mm thick skim with an NHL based plaster is pretty DIYable - goes off quicker, and using a fine enough sand any mistakes can be tidied with a scraper / sandpaper

I’ve also found that if you buy it premixed so all you have to do is add water then many “non-heritage” plasterers are keen to have a go, I got a few rooms done that way at a fraction of the cost of “heritage plasterers”

I'm not sure any NHL lime plaster that 'goes off quicker' is DIYable. There's nothing worse than realising your 'chasing the gear' when you've barely covered 1/4 of the wall.

I don't know, I think if you're going down the self plastering route its a whole different world. I had to learn using Lime Green NHL products which have accelerators and they were horrible. I'd recommend something a bit more 'heritage', a lime putty based bag of ready mix. It'll happily sit in the bucket all day nice and fresh waiting to be spread on the wall. It also worked out better value than the NHL powdered stuff as it seemed to go so much further. Always 2 coats for skim with me though, I don't know how anyone gets away with one.

 

[a twig]

Did you use a bonding agent to the old plaster Twig?

No, just gave it a good damping down with a hand pumped sprayer - did have to be meticulous about getting the old adhesive off etc

 

[a twig]

I'm not sure any NHL lime plaster that 'goes off quicker' is DIYable. There's nothing worse than realising your 'chasing the gear' when you've barely covered 1/4 of the wall.

I don't know, I think if you're going down the self plastering route its a whole different world. I had to learn using Lime Green NHL products which have accelerators and they were horrible. I'd recommend something a bit more 'heritage', a lime putty based bag of ready mix. It'll happily sit in the bucket all day nice and fresh waiting to be spread on the wall. It also worked out better value than the NHL powdered stuff as it seemed to go so much further. Always 2 coats for skim with me though, I don't know how anyone gets away with one.

Agree if you are doing a whole wall from bare stone, but here we are talking about a 2-3mm skim over existing plaster - definitely isn’t taxing, you can even do it with a rubber grouting float if you don’t get on with “the tools”

I used to mix up NHL3.5 with plastering sand from the local builders merchant (no accelerants - personally wouldn’t touch Lime Green, much better and more DIY friendly premixed products out there like Reabilita Cal AC )

That mix would give plenty of working time (up to 4 hours depending on conditions) and would be ready for paint in 48-72 hours rather than the significantly longer times with fat lime, which was the main advantage I was referring to in terms of going off quicker.

Genuinely never needed two skim coats in situations like this - occasionally when plastering over wood wool boards I’d need two but otherwise just slap and spread

 

[a twig]

If you really want the easy route, properly clean down the walls then just shove fill and finish into the cracks using a mudding knife, quick sand and then two coats of your chosen colour of Earthborn.

Yes it isn’t overly breathable but if all your doing is crack filling then it doesn’t really matter as over 90% of the wall will be, and it’s fairly flexible so unlikely to cause future problems

 

[Kearn]

I guess I would have to understand the differences...

You really do need to - fundamental elements of how your old building works. Take the time to understand now before making decisions that cannot easily be reversed and will have consequences down the lien.
Incidentally, there’s no point wasting (a lot) of cash on an unnecessary lime skim, that looks in damn good shape, you’re lucky. Fill any small imperfections - cracks with lime putty or small holes, polyfilla wont harm. Then finish to suit aesthetics, but keep it breathable to enable future custodians to undo what you’ve done if they don’t like paper, or go over your breathable finish with another colour. Limewashs/distempers or a couple of specialist paint suppliers are genuinely breathable in the context of what an old building requires, not a human. Limewash will also help even out the finish by levelling out smaller imperfections.

But if you’re after a square, flat and contemporary look, I dare say this might not be the right building…

 

[davide2023]

Thank you all of the really valuable comments.

As Kearn just said, I am trying to understand what it is the best for the property: funny enough I never knew anything different then lime for plastering until recently, so the idea that I could hire a plasterer to skim coat my walls and (potentially) end up with a problem instead of a solution didn't cross my mind.

Clearly I have more to read, so any other solution/idea is very welcome at this stage

 

[davide2023]

I'll resume this thread once again: a plasterer (that has been recommended to me) came to check the walls and suggested to re-skim the wall using fiberglass mesh and multifinish. While the fiberglass mesh makes sense to me, I am not sure about the multifinish based on the suggestions in this thread and what I have found unde the wallpaper in the other room (thread here). I am also lining up and electrician to works on these walls as well, so further disruption to this plaster is on the cards as well.
What do you think of the suggestion I have received?

 

[Lacan07]

I'll resume this thread once again: a plasterer (that has been recommended to me) came to check the walls and suggested to re-skim the wall using fiberglass mesh and multifinish. While the fiberglass mesh makes sense to me, I am not sure about the multifinish based on the suggestions in this thread and what I have found unde the wallpaper in the other room (thread here). I am also lining up and electrician to works on these walls as well, so further disruption to this plaster is on the cards as well.
What do you think of the suggestion I have received?

I guess he's recommending fibreglass mesh to avoid any future cracking, gypsum has no tolerance to movement at all but old houses move all the time. Some people might say the fibre glass is overkill or even a waste of time but on the other hand it might give you many years of crack free walls. You have to decide whether you need the room to be breathable or not. If not then multi finish is fine, and cheaper. You'll need to allow the electrician to do his first fix before you call the plasterer in, then the electrician returns for the second fix.

 

[skinnymalinky]

I'll resume this thread once again: a plasterer (that has been recommended to me) came to check the walls and suggested to re-skim the wall using fiberglass mesh and multifinish. While the fiberglass mesh makes sense to me, I am not sure about the multifinish based on the suggestions in this thread and what I have found unde the wallpaper in the other room (thread here). I am also lining up and electrician to works on these walls as well, so further disruption to this plaster is on the cards as well.
What do you think of the suggestion I have received?

99% of plasterers aren't going to suggest lime and they might look at you as if you've just grown a second head if you suggest it... but that's purely due to the lack of knowledge, skill and care of the average tradesperson in the UK in 2023.

When I got my rewiring done, I got one room plastered (with gypsum) as it was in a relatively bad state and I needed a finished room to use as my home office. One plasterer at that time suggested using mesh and one suggested mesh was a waste of time. If you're going with this approach, you'd probably be better to get different quotes and compare the price of doing it with/without the mesh

However, if I were you, I'd wait until the electrical work has been done then assess the damage at that point. One pragmatic option might be to ask a plasterer (your electrician might use/recommend one) to 'make good' the holes from the rewiring and also patch up the existing cracks with Easifill or whatever at the same time. This way you will still be maintaining most of the original (breathable) plaster and will save you a lot of money and hassle on applying a full finishing coat.

Sounds like you still haven't worked out if you need/want to maintain breathability though so you probably want to research that and make a decision before you go any further. The basic summary is usually: if you have a solid-walled house built before c. 1920s, then you'll want to keep using breathable materials.

 

[davide2023]

I understand the reason to use breathable materials, but with so many houses in the UK built 100 or over years ago, why is it so hard to find somebody that works with lime? Shouldn't that be more mainstream? Maybe that's a stupid question...

 

[MatthewC]

I understand the reason to use breathable materials, but with so many houses in the UK built 100 or over years ago, why is it so hard to find somebody that works with lime? Shouldn't that be more mainstream? Maybe that's a stupid question...

The fact of the matter is that modern tradesmen are simply not interested in the old techniques (probably becasue it takes more time/skill to do and more time to set). Their standard response is "You don't believe all that stuff, do you?", followed by "I'll slap a bit of thistle on that and it'll look great" - which is does for a short while (or even a few years) but, eventually, their folly is exposed. I despair at some of the poor advice you can find on YouTube.

As a policy you should think VERY hard before mixing old with new. The reason is best seen at the base of old walls where the brick or stone has eroded on the outside leaving some very solid cement pointing doing nothing useful. This is because anything cementatious (i.e. almost everything modern) is impervious, whereas lime isn't - lime (and hence lime mortar) is very porous and so allows the flow of water or water vapour, usually preferentially through the mortar. However, with cement pointing any dampness in that wall is only able to track out through the brick/stone and hence, when it freezes, the water expands and the outer part of the brick/stone falls off. Leave it twenty years and the brick/stone is retreating inwards by a huge amount and an expensive repair is required.

Limestone (and hence lime mortar) also expands and contracts with temperature, where cement doesn't (well, if it does it is several orders of magnitude less than lime). So after a good few years, any cement-based material patching up limestone is liable to crack and fall off, because the limestone has been gently flexing with temperature but the cementatious stuff hasn't - hence stress and ultimately failure at the join.

Old buildings (such the the 900 year old Grade 1 listed church opposite my house) have only survived so long because of the use of the correct lime-based materials, and this is what must still be used - repairs from thirty years ago are already showing their age, but repairs done centuries ago are still there - you can see the join but there's no crack. If you value your old building, understand why it has survived and do the same.

HTH

Matthew
(see my blog at http://houseintheenchantedforest.blogspot.com/ if you have an hour to browse through it, or buy my book "Rotas, Rules and Rectors" which includes a good chunk about looking after old churches - see http://www.beingachurchwarden.com/)

 

[skinnymalinky]

I understand the reason to use breathable materials, but with so many houses in the UK built 100 or over years ago, why is it so hard to find somebody that works with lime? Shouldn't that be more mainstream? Maybe that's a stupid question...

No I think it's a very good question It does seem to be a huge problem really - even from my limited experience. There seems to be a serious skill shortage and there is a lot of misinformation and misunderstanding out there

My understanding is that last few generations of plasterers (same applies to other trades) have only ever been trained using 'modern' materials and practices, which are easier and cheaper to use - and therefore the traditional ways have fallen out of common practice. I sort of imagine on day 1 of a plastering course, students are told about 'ye olde lime plaster' for 5 minutes and that's the last time they ever think about it.

Obviously the more niche the practice becomes, the more expensive it becomes... which in turn puts people off from doing things 'the right way'. If a plasterer quotes £1000 for a gypsum skim vs a specialist using lime quotes £5000, of course most people will go with the cheaper option and hope for the best. Same goes for pointing - the local builder using cement is going to cheaper than a real stonemason using lime.

 

[Lacan07]

I understand the reason to use breathable materials, but with so many houses in the UK built 100 or over years ago, why is it so hard to find somebody that works with lime? Shouldn't that be more mainstream? Maybe that's a stupid question...

You have to realise gypsum was developed for convenience, there's a huge practical discrepancy between modern plaster and lime. Gypsum is cheaper, quicker and easier. A decent spread can complete a wall from brick to finish in a day if required, no need to keep returning to site. There's a multitude of variables and knowledge you need to learn with lime plastering, lime specialists take there mixes very seriously. I've encountered a few of them and they were arrogant so and so's who didn't appreciate amateurs like me picking up the trowel and having a go. The whole industry that's built up around 'NHL' lime hasn't helped that either. They hate that stuff but its the most easily obtained and readily used at the moment.

I also think most plasterers are probably worried about pricing a job that involves lime and that its more hassle than its worth. Don't forget up to recently its probably only been the preserve of the very rich and heritage sites. It's only in the last decade or so that attitudes towards old houses have started to change as we realised the damage we were doing to them. You'd expect interest in lime to only grow from this point and more plasterers to get involved but I wonder if all this will be brought to an abrupt end as the climate zealots try and demonise old housing stock. They're already pushing to get rid of gas boilers and there's been murmurs about wood burners.

The question of how breathable you want your house to be is both a personal and practical dilemma. Generally I see people gypsum upstairs and lime downstairs, the thing to consider here is internal moisture levels and condensation. If your satisfied you've dealt with any / all 'causes' of damp and you're not one to believe in rising damp than you may even feel emboldened to gypsum downstairs.

 

[davide2023]

I am continuing my deep dive into the topic of plastering, and stumbled on this: https://www.instagram.com/p/CnZSS0opR35/
I am wondering if anybody has used it and whether it would work well for my project?

 

[a twig]

I am continuing my deep dive into the topic of plastering, and stumbled on this: https://www.instagram.com/p/CnZSS0opR35/
I am wondering if anybody has used it and whether it would work well for my project?

Scroll back up?

 

[davide2023]

Scroll back up?

Yep! Sorry.

Just reread the whole thread one more time.

I am seriously thinking to go down the DIY route now, as plasterer seems to be really hard to get hold off and have extremely long waiting times, on top of the whole lime/gympsum conversation we are having.

I wrote to https://www.lincolnshirelime.co.uk/ and they suggested me the lime green solo + lime green primer and mesh. However, if the SecilTek is a better product, I can definitely see if I can get some of it.

 

[Lacan07]

Yep! Sorry.

Just reread the whole thread one more time.

I am seriously thinking to go down the DIY route now, as plasterer seems to be really hard to get hold off and have extremely long waiting times, on top of the whole lime/gympsum conversation we are having.

I wrote to https://www.lincolnshirelime.co.uk/ and they suggested me the lime green solo + lime green primer and mesh. However, if the SecilTek is a better product, I can definitely see if I can get some of it.

Stay away from LG Solo, its not for amateurs, even professionals hate it. It goes off in the bucket like a bitch.