Elementary plastering questions

[skinnymalinky]

Hi all

First post so please go easy on me!

Intro: I have recently moved into a 1920s sandstone end-of-terrace in Scotland. However it's proving to be slightly more problematic than I first imagined... a common theme on this forum I imagine

So I have a few pretty basic questions that hopefully I can get some guidance on...

First one: what sort of plaster do we think this is? I'm guessing this is lime mixed with animal hair?




I've seen quite a bit of seemingly dogmatic content online about the need to maintain the same plaster, use breathable paint, etc in properties of this age. To what extent is there any scope for pragmatism here? For example, if all walls are covered with PVA and gypsum but the house was otherwise well-ventilated, is this still inevitably going to lead to a bad time? What are the other parameters here? What about internal walls vs exerior-facing walls?

My electrician had brought in local Joe Plasterer to 'make good' the raggles on the wall and I asked him to apply a finishing coat to one small room (I am living in the house while I renovate so the temptation to have at least one habitable, somewhat 'finished' room was strong). However, I later realised that this may have been a mistake given that he has just applied bog standard PVA and gypsum to walls and ceiling. There is one 'exterior' wall in this room, which is 3m high and 2.5m wide with at least 1/3 taken up by a window. Should I, for example, be taking the new plaster back off if I was smart? Or is it unlikely to be a huge problem? What if I wanted to insulate this wall in time?

Potentially related subject... On the same wall, there are two vent holes (approx. 10x10cm) - one at the top and one at the bottom, both of which reveal a small cavity. The top one has a small duct to a vent on the exterior/outside wall. I wonder what the original intended purpose was for these... The other rooms on this floor have fireplaces so I wonder if these were to let fresh air in? Or are these likely to still be required for ventilation?




OK I think that's probably more than enough questions for now


Thanks a lot for reading if you got this far!


- sm -

 

[Lacan07]

Hi all

First post so please go easy on me!

Intro: I have recently moved into a 1920s sandstone end-of-terrace in Scotland. However it's proving to be slightly more problematic than I first imagined... a common theme on this forum I imagine

So I have a few pretty basic questions that hopefully I can get some guidance on...

First one: what sort of plaster do we think this is? I'm guessing this is lime mixed with animal hair?

View attachment 9565View attachment 9566


I've seen quite a bit of seemingly dogmatic content online about the need to maintain the same plaster, use breathable paint, etc in properties of this age. To what extent is there any scope for pragmatism here? For example, if all walls are covered with PVA and gypsum but the house was otherwise well-ventilated, is this still inevitably going to lead to a bad time? What are the other parameters here? What about internal walls vs exerior-facing walls?

My electrician had brought in local Joe Plasterer to 'make good' the raggles on the wall and I asked him to apply a finishing coat to one small room (I am living in the house while I renovate so the temptation to have at least one habitable, somewhat 'finished' room was strong). However, I later realised that this may have been a mistake given that he has just applied bog standard PVA and gypsum to walls and ceiling. There is one 'exterior' wall in this room, which is 3m high and 2.5m wide with at least 1/3 taken up by a window. Should I, for example, be taking the new plaster back off if I was smart? Or is it unlikely to be a huge problem? What if I wanted to insulate this wall in time?

Potentially related subject... On the same wall, there are two vent holes (approx. 10x10cm) - one at the top and one at the bottom, both of which reveal a small cavity. The top one has a small duct to a vent on the exterior/outside wall. I wonder what the original intended purpose was for these... The other rooms on this floor have fireplaces so I wonder if these were to let fresh air in? Or are these likely to still be required for ventilation?

View attachment 9567


OK I think that's probably more than enough questions for now


Thanks a lot for reading if you got this far!


- sm -

Yes, That looks like lime, modern gypsum plaster is pink in colour.

Taking a pragmatic view people tend to lime plaster the ground floor walls whilst upstairs is often compromised with gypsum, maybe excluding external walls. Insulation is a tricky one, if I were installing IWI I would most likely keep it all breathable and avoid modern unbreathable methods like baton // rigid foam board

 

[skinnymalinky]

Yes, That looks like lime, modern gypsum plaster is pink in colour.

Taking a pragmatic view people tend to lime plaster the ground floor walls whilst upstairs is often compromised with gypsum, maybe excluding external walls. Insulation is a tricky one, if I were installing IWI I would most likely keep it all breathable and avoid modern unbreathable methods like baton // rigid foam board

Thanks so much for taking the time to reply.

Very interesting re upstairs/downstairs. What do you think is the logic behind compromising with the upstairs?

 

[malcolm]

The plaster in the opening post looks like lime to me. (Though on an android phone it does look pink if you have the blue correction switched on). I can see hairs in the base coat and the skim coat is too thick for gypsum.

My ex once painted a bare lime wall in vinyl paint as a surprise. No way I can put that right and retain the original lime finish. I'm a believer in making sure lime plaster preserved as well as yours is covered in lining paper prior to any paint. For insulation making it breathable with woodfibre board is a good plan.

Breathability of downstairs walls tends to be more important because a lot of the water ingress comes from the ground and the walls are more exposed to rain. Upstairs you don't have water from the ground (assuming the downstairs walls haven't been waterproofed on both sides) and the exterior walls are more protected by roof overhangs. Gypsum and emulsion are less likely to cause problems upstairs.

Are the holes to do with a fireplace that has been covered up?

 

[Lacan07]

Thanks so much for taking the time to reply.

Very interesting re upstairs/downstairs. What do you think is the logic behind compromising with the upstairs?

Money usually, and as Malcolm says the fact the walls upstairs are at less risk if damp ingress, especially the internal walls. Old houses are a compromise essentially. The only other thing to consider when using gypsum is condensation, moisture is supposed to pass harmlessly away through the fabric of an old building.

Its worth noting standard gypsum plasterboard is in fact perfectly breathable and with a gypsum skim over the top has a small amount of breathability (useful to know if you need to replace or overboard a ceiling). Slobbering an old wall with PVA and skimming however has no breathability.

 

[skinnymalinky]

The plaster in the opening post looks like lime to me. (Though on an android phone it does look pink if you have the blue correction switched on). I can see hairs in the base coat and the skim coat is too thick for gypsum.

My ex once painted a bare lime wall in vinyl paint as a surprise. No way I can put that right and retain the original lime finish. I'm a believer in making sure lime plaster preserved as well as yours is covered in lining paper prior to any paint. For insulation making it breathable with woodfibre board is a good plan.

Breathability of downstairs walls tends to be more important because a lot of the water ingress comes from the ground and the walls are more exposed to rain. Upstairs you don't have water from the ground (assuming the downstairs walls haven't been waterproofed on both sides) and the exterior walls are more protected by roof overhangs. Gypsum and emulsion are less likely to cause problems upstairs.

Are the holes to do with a fireplace that has been covered up?

Thanks @malcolm !

I hope the vinyl paint job wasn't why they became your ex!

Just so I understand your point on lining paper... are you advocating lining even if using a suitable breathable product?
e.g. Earthborn Claypaint, Bauwerk Lime Paint, or Distemper paints etc?

There was never any fireplace in this particular room, no. It's also the only room with the holes in it.

 

[malcolm]

The lining paper won't make the wall any more breathable. It's more of a preservation thing. It will allow the next restorer to get back to the original lime finish after future occupants have painted the wall with emulsion.

 

[skinnymalinky]

Money usually, and as Malcolm says the fact the walls upstairs are at less risk if damp ingress, especially the internal walls. Old houses are a compromise essentially. The only other thing to consider when using gypsum is condensation, moisture is supposed to pass harmlessly away through the fabric of an old building.

Its worth noting standard gypsum plasterboard is in fact perfectly breathable and with a gypsum skim over the top has a small amount of breathability (useful to know if you need to replace or overboard a ceiling). Slobbering an old wall with PVA and skimming however has no breathability.

Thanks, yeah makes sense I suppose.

I thought as much re PVA, which was why I wondering if I'd be best stripping at least the external wall back and starting again. However given it is indeed upstairs and ultimately only a small surface area (not to mention all the mess, cost) I'm probably inclined just to leave it and hope for the best

 

[skinnymalinky]

The lining paper won't make the wall any more breathable. It's more of a preservation thing. It will allow the next restorer to get back to the original lime finish after future occupants have painted the wall with emulsion.

I thought that was your point, yeah. What if I leave a firm note when I sell the house instead?

 

[Drayton]

(I am living in the house while I renovate so the temptation to have at least one habitable, somewhat 'finished' room was strong).

I'm probably inclined just to leave it and hope for the best

I'd definitely leave it be - you need somewhere to retreat to and it may never be a problem.
If it proves to need extra work in due course it can take its place on the list, and you will have more experience by then.
While any time and money spent on decorating etc might seem wasted if it does need work later, the benefit of not having everywhere a mess will outweigh this unless you are much tougher than most of us.

 

[skinnymalinky]

I'd definitely leave it be - you need somewhere to retreat to and it may never be a problem.
If it proves to need extra work in due course it can take its place on the list, and you will have more experience by then.
While any time and money spent on decorating etc might seem wasted if it does need work later, the benefit of not having everywhere a mess will outweigh this unless you are much tougher than most of us.

Hi @Drayton, I really appreciate this comment - thank you for the reassurance! I think you're probably spot on here.

Cheers

 

[Lacan07]

Thanks, yeah makes sense I suppose.

I thought as much re PVA, which was why I wondering if I'd be best stripping at least the external wall back and starting again. However given it is indeed upstairs and ultimately only a small surface area (not to mention all the mess, cost) I'm probably inclined just to leave it and hope for the best

Yeah, I'd leave it. I wouldn't get to carried away at this stage about 1 wall, it'll still be there if and when you decide to come back to it. And by then you'll have more of an idea and experience about how you want to insulate the house.