Survey on house purchase - DAMP advice

[MTrenocottage]

Hello - first time posting, probably won’t be the last! We are in the process of purchasing a house, c1900 two cottages that have been knocked into one detached house 40 years ago. Survey has confirmed every chimney breast (affecting 4 rooms upstairs and downstairs) are damp. We could see visual evidence of damp, crumbling plaster on internal walls and stained wall paper. The seller has had a quote for the work (dated 8 months ago when last sale fell through due to this very issue!) quoting £10k for removal of plaster, chemical DPC and then re plastering. Through research we have seen that lime plaster is the best for this age property to allow walls to breathe, but my question is, do we strip plaster, and still need this chemically injected damp proof before lime plastering, or can we just strip back the current plaster, let walls dry out and then lime plaster?? Any advice gratefully received. We’ve fallen so in love with this old lady of a house that is in desperate need of TLC, this damp is not putting us off buying the house but we want to make sure we heal it in the absolute right way!! Thanks in advance for your advice.

 

[Cubist]

Hi there and welcome,
None of the chemical anti-damp systems are worth any consideration whatsoever. They do nothing but put your money in someone else's pockets and some even cause further damage to the house. Key actions to remediate damp in chimney breasts are to prevent water ingress from above while ensuring the flues are open to air circulation and replace any gypsum plasters with lime products.

Other members will be along soon to echo these thoughts and add others.

Good luck and enjoy,
Cubist

 

[MTrenocottage]

Hi there and welcome,
None of the chemical anti-damp systems are worth any consideration whatsoever. They do nothing but put your money in someone else's pockets and some even cause further damage to the house. Key actions to remediate damp in chimney breasts are to prevent water ingress from above while ensuring the flues are open to air circulation and replace any gypsum plasters with lime products.

Other members will be along soon to echo these thoughts and add others.

Good luck and enjoy,
Cubist

Thank you for your advice, much appreciated.

 

[Lacan07]

Hello - first time posting, probably won’t be the last! We are in the process of purchasing a house, c1900 two cottages that have been knocked into one detached house 40 years ago. Survey has confirmed every chimney breast (affecting 4 rooms upstairs and downstairs) are damp. We could see visual evidence of damp, crumbling plaster on internal walls and stained wall paper. The seller has had a quote for the work (dated 8 months ago when last sale fell through due to this very issue!) quoting £10k for removal of plaster, chemical DPC and then re plastering. Through research we have seen that lime plaster is the best for this age property to allow walls to breathe, but my question is, do we strip plaster, and still need this chemically injected damp proof before lime plastering, or can we just strip back the current plaster, let walls dry out and then lime plaster?? Any advice gratefully received. We’ve fallen so in love with this old lady of a house that is in desperate need of TLC, this damp is not putting us off buying the house but we want to make sure we heal it in the absolute right way!! Thanks in advance for your advice.

Hi

I think the theory behind a liquid DPC is sound but the people that implement them are often not, in any case its irrelevant to your particular issue. 'Tanking' however is a dreadfully damaging exercise and should be avoided at all costs.

I would put that 10k back in your pocket, but unfortunately the Lord giveth with one hand and he taketh with the other! Check for any sources of water ingress and fix, make sure the chimneys are well ventilated, remove any unbreathable material from the walls and lime plaster. If you find the original plaster is still present and its sound on the wall then LEAVE ALONE! Don't be tempted to remove all plaster up to 1 - 1.5 meters, only remove the loose plaster. That plaster is the mutts nuts and preserving it will save you a hell of a lot of hassle and money. A skim is cheaper and quicker than a 3 coat lime replacement.

 

[MTrenocottage]

Wow it’s like you’ve seen the report for the work quoted which Recommended tanking slurry, striping walls up to 1.5m etc! I am very pleased I found this forum to get some advice to reenforce our research on how to do it properly!!
Our survey has said no issues with chimney water ingress etc and flashing around chimney is sound.
Interesting you say to only plaster where needed, not whole wall, we hadn’t considered this. Thanks for your comments, we appreciate it.

 

[MTrenocottage]

Hi

I think the theory behind a liquid DPC is sound but the people that implement them are often not, in any case its irrelevant to your particular issue. 'Tanking' however is a dreadfully damaging exercise and should be avoided at all costs.

I would put that 10k back in your pocket, but unfortunately the Lord giveth with one hand and he taketh with the other! Check for any sources of water ingress and fix, make sure the chimneys are well ventilated, remove any unbreathable material from the walls and lime plaster. If you find the original plaster is still present and its sound on the wall then LEAVE ALONE! Don't be tempted to remove all plaster up to 1 - 1.5 meters, only remove the loose plaster. That plaster is the mutts nuts and preserving it will save you a hell of a lot of hassle and money. A skim is cheaper and quicker than a 3 coat lime replacement.

Wow it’s like you’ve seen the report for the work quoted which Recommended tanking slurry, striping walls up to 1.5m etc! I am very pleased I found this forum to get some advice to reenforce our research on how to do it properly!!
Our survey has said no issues with chimney water ingress etc and flashing around chimney is sound.
Interesting you say to only plaster where needed, not whole wall, we hadn’t considered this. Thanks for your comments, we appreciate it.

 

[stuart45]

Chimney breasts can sometimes show areas of dampness due to the plaster having hygroscopic salts coming through from the flues.
Modern chimney stacks also have lead trays built into them to help prevent penetrating damp. Years ago they weren't used as the chimneys were generally in use every day in the wetter, colder seasons, and this helped keep them dry.

 

[MTrenocottage]

Thank you for your comment. Is there anything specific we need to do to remove the hygroscopic salts from the walls? Treatments etc? Or is it a case of scraping away and replastering (affected areas only)?
I do think this is exactly what the damp areas are now I’ve looked into it more. Top of upstairs chimney breasts and ground level on the downstairs chimney breasts.
I might just need to get myself an aga too to maintain the warmth around the house!!! Any excuse!

 

[malcolm]

If the chimney is not in use it makes sense to have a ventilated cowl on top. That lets air evaporate away from inside the chimney while keeping rain water out. One of mine was blocked at the top and was very damp inside.

 

[stuart45]

Thank you for your comment. Is there anything specific we need to do to remove the hygroscopic salts from the walls? Treatments etc? Or is it a case of scraping away and replastering (affected areas only)?
I do think this is exactly what the damp areas are now I’ve looked into it more. Top of upstairs chimney breasts and ground level on the downstairs chimney breasts.
I might just need to get myself an aga too to maintain the warmth around the house!!! Any excuse!

There are various methods that people use for this problem, although how effective they are in the long term I can't really be sure of. One method was to remove the plaster, render with with sand/cement 3/1 with added waterproofer and salt neutralizer. Another was treat the walls with neutralizer and use lime plaster. Another neutralizer the dot and dab.
I've seen them all used on jobs, and I'm sure they probably work in the short term, but I don't call round 10 years later to check. I'm a bricklayer by trade, and this type of work is done by the plasterers, so I can't really give you the best advice. If it was mine, I would get the flues swept, remove the plaster, treat the brickwork and replaster in lime.

 

[Lacan07]

Thank you for your comment. Is there anything specific we need to do to remove the hygroscopic salts from the walls? Treatments etc? Or is it a case of scraping away and replastering (affected areas only)?
I do think this is exactly what the damp areas are now I’ve looked into it more. Top of upstairs chimney breasts and ground level on the downstairs chimney breasts.
I might just need to get myself an aga too to maintain the warmth around the house!!! Any excuse!

Salts occur where the soot interacts with the lime mortar so sometimes just by looking at the chimney you can trace which direction or diagonal the flue travels inside. On one of my chimneys downstairs (now back to bare brick) it can be seen to clearly run diagonal, right to left - the mortar is a darker (wetter) colour because its attracting the moisture in the air. The traditional way of dealing with this would be to add cow sh*t to the lime scratch coat. Its something to do with the mucus membranes in the stomach, I don't know exactly, but it's supposed to prevent the damp patches from coming through. I don't think there's another way to keep the salts at bay and the brick work breathable. Any other way would involve modern materials / methods.

 

[Lacan07]

Wow it’s like you’ve seen the report for the work quoted which Recommended tanking slurry, striping walls up to 1.5m etc! I am very pleased I found this forum to get some advice to reenforce our research on how to do it properly!!
Our survey has said no issues with chimney water ingress etc and flashing around chimney is sound.
Interesting you say to only plaster where needed, not whole wall, we hadn’t considered this. Thanks for your comments, we appreciate it.

If you're not going to have a liquid dpc or tank the walls there's no need to remove plaster to 1.5 meters. Satisfy yourself you've found the causes of the damp - fix those causes - and then remove all loose plaster. How you repair the wall is dependent on what type of plaster is present and what you want to achieve (skimmed or wall papered)

 

[malcolm]

Damp only happens when more water is getting in than can get out again.

You deal with it by stopping water getting in and also by giving the water that does get in some way out.

Only stopping the water from getting out by tanking or cement iwould be a poor strategy. Letting water out with breathable stuff like lime plaster and clay paints is good.

Modern emulsion paints are surprisingly bad. It's them and cement and poor chimney venting choices that cause the trouble in the first place.

There is no need for silly injected damp rubbish on your chimney. Any damp that only occurs in the chimney won't be coming up from the ground. And there is no need as there would be a fair bit more work needed to make an old building work like a new building.