Lime plastering on party wall (semi-detached house)

[lizziecupcakes]

hello
just seeking some advice. I am purchasing a semi-detached Edwardian property that's currently gypsum plastered. we are going to get rid of that and replace it with NHL lime plaster.

I have no idea what my neighbour uses for plastering, but it's most likely to be gypsum. So, I'm not sure what to do about the party wall within all the rooms. Should I continue to lime plaster the party wall? I'm not sure about the breathability on the party wall and not sure what to expect.

does anyone have any experience or advice about this?

thank you

 

[Stevers]

Gypsum plaster is breathable (any cement render that's underneath less so), but gypsum plaster is intolerant of salts and damp. Is there a problem with the plaster that's there now?

We were damp proofed here as part of the mortgage conditions, and apart from in the basement where they had to redo the tanking (skimmed with gypsum plaster again), it's a small proportion of the original gypsum 'damp proofing' that has failed and been reworked by me after it went out of warranty. Some of that was actually because it was deemed to be insufficiently plumb! Only my chimney breast repair used NHL renders. I'm not a fan of cement render and pink plaster, but quite happy to leave it be if it's smooth, reasonably plumb and sound, as I do the considerable areas of original lime plaster that have survived in good shape.

In the basement room with that chimney breast I've had to patch quite large areas of the (above ground) lime plaster that had perished, and this time I used an NHL render topped with a skim of Thistle One Coat (gypsum). This is a bit of an experiment, but some of it had been chased out and back-filled with Thistle One Coat in 1997 and that was still perfectly sound. I'm working for myself, and it's my problem if it goes wrong, but have no reason to think it will.

 

[paulc]

Gypsum plaster is breathable (any cement render that's underneath less so), but gypsum plaster is intolerant of salts and damp. Is there a problem with the plaster that's there now?

Whilst gypsum will tolerate getting damp once or twice, it will turn to mush if constantly damp.
The other thing it doesn't like is heat. Anything over 50°C, and it flakes off the wall. So if you are plastering around a fireplace, lime is much more suitable.

 

[Lacan07]

hello
just seeking some advice. I am purchasing a semi-detached Edwardian property that's currently gypsum plastered. we are going to get rid of that and replace it with NHL lime plaster.

I have no idea what my neighbour uses for plastering, but it's most likely to be gypsum. So, I'm not sure what to do about the party wall within all the rooms. Should I continue to lime plaster the party wall? I'm not sure about the breathability on the party wall and not sure what to expect.

does anyone have any experience or advice about this?

thank you

If there's no physical signs of damp on your walls then leave be, why put yourself through the expense. By far the most common cause of damp is high external ground and poorly retro fitted concrete floors. Rising damp is very rare unless you're in an area with a high water table. I assume as Edwardian you have a slate DPC which is mostly likely in good order.

As you say your neighbours side of the party wall is most likely gypsum so it won't be breathable (both sides need to be open for proper breathability).

 

[aockenden]

Under other circumstances I tend to push-back on the idea that a wall needs to be fully breathable on both sides in order to gain a benefit from redoing stuff in lime, as I think that’s an “all or nothing” fallacy, and I definitely believe that having one side of the wall breathable is WAY better than having neither side of the wall breathable.

However, given that this is a party wall and should therefore be warm and not subject to much condensation, I agree with the above sentiments that it’s probably not worth your time assuming the existing surface is sound and looks good.

That recommendation might change again though if there’s an open functional chimney anywhere on the wall in question, as that opens you up to risks from water ingress from above (and other salt-related issues) which redoing in Lime could significantly benefit.

 

[lizziecupcakes]

Thanks all. Really great points from you all. I appreciate it!

The party wall in the master bedroom also has a chimney breast which is covered up. I’m thinking about uncovering this and hoping it will reveal a lovely fireplace. I want to keep this, so will want lime plastering over this. But to the sides of the chimney are the party walls. So, i’m thinking i’ll keep that as gypsum plaster.

This means that the party wall will have lime plastering over the chimney breast/fireplace while the rest of the party wall will be gypsum.

Would you add wood fibre board insulation to the party wall? What about over the chimney breast (sorry if that’s a silly question - I hadn’t thought about that before).

 

[lizziecupcakes]

And yes @Lacan07 , you’re right. It’s Edwardian, raised floor with slate DPC which I’m hoping is in good order. The surveyor thought it’s most likely to be in good order

 

[aockenden]

Thanks all. Really great points from you all. I appreciate it!

The party wall in the master bedroom also has a chimney breast which is covered up. I’m thinking about uncovering this and hoping it will reveal a lovely fireplace. I want to keep this, so will want lime plastering over this. But to the sides of the chimney are the party walls. So, i’m thinking i’ll keep that as gypsum plaster.

This means that the party wall will have lime plastering over the chimney breast/fireplace while the rest of the party wall will be gypsum.

Would you add wood fibre board insulation to the party wall? What about over the chimney breast (sorry if that’s a silly question - I hadn’t thought about that before).

As for whether to insulate that party wall, again since it’s a party wall it should be a “warm” wall already, so the decision to insulate or not would mostly be judged on the value of sound insulation benefit, not thermal benefit. If you can hear your neighbors shagging then maybe it’s worth insulating, otherwise maybe not.

 

[lizziecupcakes]

Haha @aockenden that reminds me of university halls life (gross). I totally forgot about Sound insulation

 

[lizziecupcakes]

Quick question @Lacan07 @aockenden @paulc @Stevers : what about applying lime plaster to walls that aren’t facing the outside/external environment? In other words, the internal walls within the house. I’ve attached a floor plan and highlighted what i mean by "internal walls".

internal walls are circled red
external walls are blue

For these “internal walls”, would you apply lime plastering to them? Or does it make more sense to only apply lime plastering to only the walls facing the external/outside environment? i.e. to the outer border walls inside.

 

[Lacan07]

Quick question @Lacan07 @aockenden @paulc @Stevers : what about applying lime plaster to walls that aren’t facing the outside/external environment? In other words, the internal walls within the house. I’ve attached a floor plan and highlighted what i mean by "internal walls".

internal walls are circled red
external walls are blue

For these “internal walls”, would you apply lime plastering to them? Or does it make more sense to only apply lime plastering to only the walls facing the external/outside environment? i.e. to the outer border walls inside.

View attachment 13724

Lizzie, I'm going to ask again, have you actually got any damp walls on the ground floor? Exactly what state are they in, are they a cause for concern? Did the surveyor flag this up as an issue? Literally 1000's of old houses have been renovated with modern plaster and cope just fine.

Many people compromise by using gypsum on internal walls and saving the lime for external walls, especially on the upper floors. I have done this myself. The only problem with this is it can be quite a chore working out how to paint the rooms, for example keeping it the colour consistent. Bear in mind breathable paints are as expensive as the posh paints. Limewash is cheap but a pain in a**e imho.

 

[a twig]

If it’s any consolation I’ve found earthborn clay paint pretty consistent on both gypsum and lime

 

[Lacan07]

If it’s any consolation I’ve found earthborn clay paint pretty consistent on both gypsum and lime

In my bathroom I decided to use Fenwick and Talbot who supply clay paint and normal paint. I picked a colour and used the clay paint for the external wall and the scrubbable vinyl matt for the rest of the walls. The clay paint is a bit more matt and a little lighter in shade but it doesn't look too much out of place. I didn't want to use clay paint on all the walls in a bathroom. I wonder if silicate paint would be a good choice too? All these paints are expensive though.

 

[lizziecupcakes]

Lizzie, I'm going to ask again, have you actually got any damp walls on the ground floor? Exactly what state are they in, are they a cause for concern? Did the surveyor flag this up as an issue? Literally 1000's of old houses have been renovated with modern plaster and cope just fine.

Many people compromise by using gypsum on internal walls and saving the lime for external walls, especially on the upper floors. I have done this myself. The only problem with this is it can be quite a chore working out how to paint the rooms, for example keeping it the colour consistent. Bear in mind breathable paints are as expensive as the posh paints. Limewash is cheap but a pain in a**e imho.

Hi @Lacan07 ! thanks for responding!

So... there hasn't really been any damp highlighted in the house at all by the surveyor nor us. It's Edwardian, 1906-10 period, and has been gypsum plastered (no insulation).

There is a tiny spot of damp in the kitchen (it's not on an external facing wall but an internal partition wall where there used to be a cold storage place next to the kitchen, but the previous owners about 50 years ago knocked through it and left an open partition wall. There is a spot of damp on that, which the surveyor said there isn't much we can do about it as it's down to lack of an DCP when the previous owners took the wall down. We will do a kitchen extension at some point in the future, so the kitchen isn't a big concern for us as we will change it.
Other than that, there's no damp anywhere. not even upstairs, nor chimney breasts. The floorboards look ok. There is a bit of damp on the bedroom party wall though that's just beneath some cracked lead flashing and cracked parapet wall (the surveyor thinks it's down to that - mild parapet leak). There's also a poorly ventilated loft (but that's nothing to do with the plastering).

BUT (that's a heavy but), I am concerned about damp occurring while i live in it. This will be my forever home I think. hence why I have been deeply exploring the lime plastering route.

Now, I am starting to think just doing the external facing walls with lime plaster will be enough (i.e. the walls that actually make contact with the outside environment). All internal walls can be gypsum plastered. I'm so glad I asked one here, as I was originally going to lime plaster everything which would be costly.

I want to also use wood fibre boards for insulation, rather than the modern insulation boards. I'm not sure if wood fibre boards work with gypsum though.

Also, I note that you wrote: Many people compromise by using gypsum on internal walls and saving the lime for external walls, especially on the upper floors.
Just wondering, why the upper floors? Thank you

 

[lizziecupcakes]

btw @Lacan07 , I'd love to see pics of your lime plastered walls and the paint you've chosen!

 

[mardinor]

Lizzie, to state the bleedin' obvious, damp needs a water source. Unless there's a pipe leak, roof leak or condensation that usually comes from the outside and usually from ground level.

 

[lizziecupcakes]

Lizzie, to state the bleedin' obvious, damp needs a water source. Unless there's a pipe leak, roof leak or condensation that usually comes from the outside and usually from ground level.

Mardinor, yes i know this as do others. i’m not sure what point you’re making though. Please can you explain What’s that got to do with me using lime plastering? Many people use lime plastering to prevent future damp problems, they don’t just use it to treat a current active damp problem. Im also in the planning stages of my reno so i’m asking those who have lime plastering experience about their experiences and ideas behind their methods.

 

[Lacan07]

Hi @Lacan07 ! thanks for responding!

So... there hasn't really been any damp highlighted in the house at all by the surveyor nor us. It's Edwardian, 1906-10 period, and has been gypsum plastered (no insulation).

There is a tiny spot of damp in the kitchen (it's not on an external facing wall but an internal partition wall where there used to be a cold storage place next to the kitchen, but the previous owners about 50 years ago knocked through it and left an open partition wall. There is a spot of damp on that, which the surveyor said there isn't much we can do about it as it's down to lack of an DCP when the previous owners took the wall down. We will do a kitchen extension at some point in the future, so the kitchen isn't a big concern for us as we will change it.
Other than that, there's no damp anywhere. not even upstairs, nor chimney breasts. The floorboards look ok. There is a bit of damp on the bedroom party wall though that's just beneath some cracked lead flashing and cracked parapet wall (the surveyor thinks it's down to that - mild parapet leak). There's also a poorly ventilated loft (but that's nothing to do with the plastering).

BUT (that's a heavy but), I am concerned about damp occurring while i live in it. This will be my forever home I think. hence why I have been deeply exploring the lime plastering route.

Now, I am starting to think just doing the external facing walls with lime plaster will be enough (i.e. the walls that actually make contact with the outside environment). All internal walls can be gypsum plastered. I'm so glad I asked one here, as I was originally going to lime plaster everything which would be costly.

I want to also use wood fibre boards for insulation, rather than the modern insulation boards. I'm not sure if wood fibre boards work with gypsum though.

Also, I note that you wrote: Many people compromise by using gypsum on internal walls and saving the lime for external walls, especially on the upper floors.
Just wondering, why the upper floors? Thank you

Well damp issues usually occur on the ground floor and when you mention damp to people they instantly think of the dreaded 'rising damp'. The thing about rising damp is it cant rise much beyond a metre so it's not considered an issue on upper floors. But the other thing about rising damp is it's quite rare and over played by unscrupulous damp proofing companies trying to make money. Your house will almost certainly never experience it in its life time. The most common causes of damp (and the biggest threat to your house) are high external ground, retro fitted concrete floors, external concrete render or modern paint and faulty guttering / roofs. Only the last two can affect your walls on the upper levels. Therefore it's much safer to utilise modern plaster on the upper floors.

 

[Lacan07]

Hi @Lacan07 ! thanks for responding!

So... there hasn't really been any damp highlighted in the house at all by the surveyor nor us. It's Edwardian, 1906-10 period, and has been gypsum plastered (no insulation).

There is a tiny spot of damp in the kitchen (it's not on an external facing wall but an internal partition wall where there used to be a cold storage place next to the kitchen, but the previous owners about 50 years ago knocked through it and left an open partition wall. There is a spot of damp on that, which the surveyor said there isn't much we can do about it as it's down to lack of an DCP when the previous owners took the wall down. We will do a kitchen extension at some point in the future, so the kitchen isn't a big concern for us as we will change it.
Other than that, there's no damp anywhere. not even upstairs, nor chimney breasts. The floorboards look ok. There is a bit of damp on the bedroom party wall though that's just beneath some cracked lead flashing and cracked parapet wall (the surveyor thinks it's down to that - mild parapet leak). There's also a poorly ventilated loft (but that's nothing to do with the plastering).

BUT (that's a heavy but), I am concerned about damp occurring while i live in it. This will be my forever home I think. hence why I have been deeply exploring the lime plastering route.

Now, I am starting to think just doing the external facing walls with lime plaster will be enough (i.e. the walls that actually make contact with the outside environment). All internal walls can be gypsum plastered. I'm so glad I asked one here, as I was originally going to lime plaster everything which would be costly.

I want to also use wood fibre boards for insulation, rather than the modern insulation boards. I'm not sure if wood fibre boards work with gypsum though.

Also, I note that you wrote: Many people compromise by using gypsum on internal walls and saving the lime for external walls, especially on the upper floors.
Just wondering, why the upper floors? Thank you

So I think what determines whether you lime your walls or not is the question of whether you decide to insulate them or not. And I guess if this is your forever house and this is your time to renovate then you most likely are going to insulate. If that's the case then youre forced to make the decision about whether you want the walls breathable or not. There's no point using wood fibre board against gypsum, you would only use rigid foam board with modern plaster. If you want breathable walls you'll have strip your walls back to brick, lime plaster a base coat, attach wood fibre boards and finally a 2 coat skim with netting to finish. There's considerable expense in that. Far be it from me tell you how to enjoy your house but would it be worth living in it through a Winter (if you havent already) and see how you feel? Because if you decide not to insulate the walls there's no reason to lime the walls imho

 

[Lacan07]

btw @Lacan07 , I'd love to see pics of your lime plastered walls and the paint you've chosen!

I'll post some when I return this evening, still a work in progress I'm afraid.