Plastering 1920s house

[Georgiarobinson2021]

So I've been reading here there and everywhere about plastering old houses with lime plaster. We're about 4 weeks off completing on a house built in 1927, we have an issue of penetrating damp from a roof leak 7 years ago that's was never redecorated or bought back to brick. We also have damp round the bottom of the house on the outer inside walls aka under Windows and on gable end. We've been informed by damp and timber specialist that this is due to the house being cement pebbledashed down to the floor. We will be taking the bottom half of the outside render off to allow the house to breathe, just repointing. I've just been reading through the heritage home website and they've said not to get a damp proof course because it doesn't help, and also that you must not and cannot use gypsum plaster in an old home. I was wondering if anyone has any advice contrary to this as it seems unreasonable and unhelpful, were a young family with a new baby and cannot afford a professional in lime plastering nor the cost of the materials for breathable paint and lime plastering. For example if we were to use plasterboard screwed onto 15mm timber to keep a gap in between the brick work and gypsum, and a 1 inch gap left at the bottom behind the skirting board, would this be sufficient breathing? We would take all the house back to brick on the inside room by room and using a dehumidifier/ heaters to help the walls dry before doing this, any advice and help would be really welcome

 

[tell80]

OP,
Why not post pics of all the damp areas - and pics of the outside rendering? Could you annotate or ID the pics?
I'd suggest that you dont do anything for the moment.
When you've supplied more info and the pics, and been advised from this site, you should have a better idea of how to proceed.

 

[jacko555]

So this may cause "differing opinions". Still, always fun.

I also have a 20's house and went through the whole heritage house / lime plaster / breathable paint concerns. Note the heritage house, while talks sense, is aimed at maybe slightly older houses.

Firstly - do you have solid walls or cavity? (See https://www.arangroup.co.uk/pages/677/How-to-identify-if-I-have-solid-or-cavity-walls/ or just google). Thickness of the wall or brick pattern can give it away. Mine is cavity, and there's more of this age than you'd expect.

The whole lime plaster / breathable walls - sure, for a solid wall. For a cavity, not so much. Any damp or moisture is evaporated in the breeze is the cavity.

I have lived in, and know plenty of victorian and Georgian houses with gypsum plaster and no ill effects.

Plenty of houses are externally rendered to the floor with cement and no ill effects.

Sure, there are plenty houses where the addition of cement / gypsum have caused a damp issue.

However, not correct to say one will certainly cause the other.

Every house behaves differently.

I'm sure the lime purists will have a bit to say on this, however, it's not as cut and dry as it looks.

 

[Pharun]

Hi, I see in your post that you were considering boarding the wall, there are thermal plus plaster boards on the market that can be dabbed onto the wall , these boards help keep the cold and damp out, however you must address your damp problem, you need to check if there is a damp course along the base of the house and make sure it has not been breached, there are also products on the market that can be used to treat the cement course of the DPC (it is like a foam in a tube that you squeeze into predrilled holes in the mortar), I personally don't have issues with gypsum products as there are damp resistant plasters available, back when I was on the tools there was a product called renovating plaster by British gypsum that we used to use , it may be called thistle dry coat now, however before you do any remedial work you must cure the damp problem first ,

 

[motorbiking]

Take the existing plaster off back to brick and use plasterboard foam, to attach 50mm of Celotex + new plasterboard. Make sure the joints are sealed foam/tape. Skim and decorate as usual. If you need any re-wiring etc, its a great time to do the lot.

If you have any open fires, you need to think about what to do with those.
The biggest problem with houses built in this era is poor thermal efficiency. 1927 could even be a English bond or similar and may even have single skin bay windows. So the U value of the walls will be 2+. The above will reduce the U value to under 0.3.