Help - Damp chimney breast

[Heather2011]

Hi,

I have a stubborn damp chimney breast issue in my home in Cardiff. We’ve replastered the affected areas a couple of times in the last 5 years and injected DPC but it doesn’t seem to solve the problem. I don’t what to do to get rid of it. Would really appreciate any expertise advise! I have attached a few pictures of the house to show where the chimney breast walls are – one in the sitting room and one in dining room.
The house is an end terrace house built in around 1910. It had DPC done around most of the walls (apart from the chimney breast walls which vents were added instead) on the ground floor in 2007.
After the work is done, most of the dampness was solved and we were pleased. However, the two chimney breast walls have been showing signs of damp patch and salt contamination. We called in the company in 2010. They admit the dampness and agreed to replaster one of the chimney breast wall around the sealed fireplace, again, no DPC was injected.
Right after the work is done, the newly plastered area starts to show salt contamination and never got dry. I had a different DPC company to check the property today and was told that the dampness could come from the chimney stack. This is because they found one of the chimney pot is cracked and another pot cover (is that the right word?) is missing. In addition, one end of the lead flashing has also become loose. They’ve advised me to fix the chimney pots and lead work, but also said that I need to replaster both chimney breast walls on the ground floor and inject DPC. I’m fine with the chimney work but really don’t want to go through the stress of replaster the walls again.
Is there any easier way to stop the dampness coming from the ground, i.e. if we just inject the DPC but not to replaster the walls, would that fix the dampness? Note that I don’t mind the salt contamination on the wall. We’ve put wall paper to cover it so as long as the wall is dry then that’ll do for me.
The other question is that I don’t really understand why the first company didn’t put any DPC in the chimney breast walls in the first place. Is it a common practice to use vent rather than DPC on these walls?
In addition, I also want to explore the option of completely seal the chimney, i.e. cap it from the top and somehow seal from the bottom as well, e.g. DPC in the base or any other ways which could seal it completely? Is this idea a totally no go or could it solve the problem?

Thanks!

Heather

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• Heather2011
• 4 Oct 2011
• 1

 

[Alastairreid]

Unused flues should be capped

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• Alastairreid
• 17 Jul 2009
• 20

and vented at the sealed over fire opening.

Ideally the chimney breast should be taken back to the brick and a sand and cement scratchcoat with added waterproofer applied.

If the ingress is caused by moisture entering through an uncapped flue i dont see how a dpc injection would help.

 

[Heather2011]

Unused flues should be capped

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• Alastairreid
• 17 Jul 2009
• 20

and vented at the sealed over fire opening.

Ideally the chimney breast should be taken back to the brick and a sand and cement scratchcoat with added waterproofer applied.

If the ingress is caused by moisture entering through an uncapped flue i dont see how a dpc injection would help.

Thanks!

Does the vent has to link to the outside (e.g. install a vent in the disused fireplace on the wall facing outside) or just a vent in the chimney breast which circulate the air inside the house and the chimney stack?

About the DPC, I'm not sure wether that would solve the problem either. I think what the DPC company says that the reason is a bit of mixure - both the broken chimney cap and rising damp. Is it a good idea to first fix the chimney cap and add vent then wait and see if that solves the issue rather than rushing into doing the whole thing?

 

[Alastairreid]

Cap the chimney and easiest to install vent inside then you will have air circulation in your flue.

 

[joe-90]

The problem is caused by condensation. Nothing to do with damp courses or cracked pots. That's a crack-pot idea.

 

[Micilin]

The problem is caused by condensation. Nothing to do with damp courses or cracked pots. That's a crack-pot idea.

 

[Alastairreid]

The problem is caused by condensation. Nothing to do with damp courses or cracked pots. That's a crack-pot idea.

Aye on the inside of the flue!

 

[roy c]

Chimney brests are nearly always the cause of damp problems to some degree. If a chimney is not being used then you have an area that is like joe said subject to condensation and also if it is "capped" off and no air vents in disused fire places then you have a situation where the air is blowing into the chimney but not exactly flowing freely thru the air vents. So you have to make sure you have a good air-flow from chimney caps like alastair showed you (called a pepperpot) thru air-vents in closed fire-places ,and also that there are no cracks in the flaunching on top of the stack, and that there are no cracks in the render on the gable wall (in your case)and that the lead soakers on the slates abutting your chimney are ok and that there are no breaks in the pointing of the ridges abutting the chimney . Also are the walls inside floated and set using sand and cement and finish plaster? Or have they been plastered with a light weight plaster (bonding or browning) and then skimmed. If this is the case then this will not keep any damp or moisture back that you have in the chimney walls. Another way of solving your damp problem inside if all else fails is to dot and dab the offending walls with poly-backed plasterboard, making sure if you do this then all joints in the boards and corners and revels have a six inch dpc strip behind them so non of the wall touches any of the plaster board. Now this may sound a bit complicated to the lay man but plasterers of some knowledge will know what I mean. I live in an 1850 old stone built house with 20" thick walls and I have knocked all the old plaster off and dubbed it out and put poly back on all outside walls and chimney walls and they were done nearly 15 years ago and I have had no problem with them since. Sorry for waffling on but I hope this helps.....

 

[Heather2011]

Thanks very much for the thorough info, Roy! That's really helpful! I almost want to print it out and use as a bible!

A few more questions just to get my head straight....Hope you don't mind.

...So you have to make sure you have a good air-flow from chimney caps like alastair showed you (called a pepperpot) thru air-vents in closed fire-places .....

This might be a silly question....where exactly should the air vent be installed?

In the sealed fireplace, there is a wooden board which covers the top. If I make a hole on this board, install a vent to circulate the air inside the chimney stack and inside the sitting room? Or does the vent needs to be installed in the back wall which circulate the air inside the chimney and outside? or do I need both?

In the dining room where the chimney breast wall is sealed, there is actually a vent installed but I remember instead of opening a proper hole in the inside wall, the worker from DPC company just drilled a few small holes (about 7?) and put a vent on top. Do you think I need to open up the hole a bit bigger to make the vent affective? Also, do I need to add any additional vent or airbrick to bring in air from outside?

...and also that there are no cracks in the flaunching on top of the stack, .....

yeah, good point. Is the pepperpot/flaunching checking usually a roofer's job? I know someone who is specialised in gutter repair but not sure if he is ok for this kind of chimney repair...

...and that there are no cracks in the render on the gable wall (in your case).....

umm...this is really tricky. the external render on the gable wall are quite old and there are quite a few lines which look like crack but if you knock on the wall it doesn't sound hollow. I had a few plasterers checked them and got mixed answers - some say it's salt coming through then painted over, some say they might be small cracks.

This is also where the disbute with the DPC company lies. They insist the dampness is caused by penetration from external render and quoted us 5k to rerender the whole external wall and if I don't do it then they'll void the DPC warrentee.

I'm really disappointed with them. The external wall has always been like that but when they did the survey a few years ago for the DPC, no one mentioned this. All I was told back then was that if I do the DPC then that would solve everything...

I have thought about renewing the render in the bottom, say 1m from ground but was warned that because these renders are so old, if they start hacking parts off then the rest might falling into parts...... Most plasterers wants me to redo the whole wall which will be very expensive....

...Also are the walls inside floated and set using sand and cement and finish plaster? Or have they been plastered with a light weight plaster (bonding or browning) and then skimmed. If this is the case then this will not keep any damp or moisture back that you have in the chimney walls. .....

I think the inside walls are sand and cemend and finish plaster.

...Another way of solving your damp problem inside if all else fails is to dot and dab the offending walls with poly-backed plasterboard, making sure if you do this then all joints in the boards and corners and revels have a six inch dpc strip behind them so non of the wall touches any of the plaster board. .....

I have started thinking of doing something similiar, if the chimney repair and vent doesn't do the job. Have seen some mesh damp proof membrane which can isolate dampness. It looks like this:

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• Heather2011
• 5 Oct 2011
• 1

The plasterboard you mentioned, is it using the similar principle as these membrane? I quite like the membrane idea but couldn't figure out where does the damp go. I imagine that damp will still get to the membrane but jjust won't go through to the plaster. If there is too much damp, will I start to see water dripping off the bottom of the membrane?...Any thoughts?

 

[roy c]

If you have had your chimney bricked up then it is wise to leave a hole out about 9"x6" and have a plastic ventilator put over it or in your case with the board that has been installed then you could cut a hole in it and put a vent over the hole. But the problem with this set up is, you will have soot coming thru the vent on occasions, so if possible it would be wiser to have a vent fitted on the straight wall or it would not do any harm to put an air-brick in the chimney from the outside, and maybe have an air-brick put in your other chimney from the outside you could put 9"x6" or 9"x9" terracotta ones in. If having these fitted make sure who ever puts them in puts them the right way up as the holes in them are sloping down from back to front so water cannot run back in!!

As for the cracks (if any) on the flaunching then it would be wise to get a good builder who has experience of building chimneys and putting on or changing pots ,to have a look at it for you .

If you have any cracks in the gable wall (no matter how big or small ) then they will let water in.


You "think" the walls are sand and cement.You have to find out for certain wether they are or not because if you dont then you might be throwing money at something when the problem lies else where!!

I have not come across that membraine that you showed but some of the other lads might have more info on that. But as you said when you seal the walls then the water stays in the walls but is contained behind whatever barrier is used. But rising damp will not rise above 1200mm any damp above that will be penertrating damp...

Hope this as cleared up a few points for you Heather

 

[Alastairreid]

Good post Roy

 

[roy c]

Good post Roy

Cheers mucka

 

[Heather2011]

If you have any cracks in the gable wall (no matter how big or small ) then they will let water in.

Big thank you again, Roy!

If I rerender the bottom part of the wall, say 1.5m from ground and leave the higher part as is, Would I have the risk of water coming in from higher part and gradually moving toward the bottom parts and cause damp again?

You "think" the walls are sand and cement.You have to find out for certain wether they are or not because if you dont then you might be throwing money at something when the problem lies else where!!

ummm....now you makes me think....I'm sure about the fireplace as it was rerendered 3 years ago and I saw how then rendered it. But....I'm not so sure about the chimney wall in the dining room. It was not re-rendered back then. The bottom part of this wall is perticularly bad - small pieces of render above the skirting board have started to fallen off. At the moment we covered it by wall paper (sorry, I know it's not the proper way)but then we can see damp coming through. Is there anyway I can tell whether the render is proper type?

 

[joe-90]

Heather. You don't seem to have a grip on what your problem is. It's nothing to do with your chimney pot. Take a look out of your window at all the millions of houses out there that have chimney posts that are wide open to the elements - yet they don't have any damp chimney breast issues do they? Neither did your house before central heating came in. Your problem is almost always found on end terraces whereby the chimney breast is very cold. Talk to your neighbours in mid terraces and you'll find they don't have the same problem - then ask yourself why that is.

The damp is from warm moist air going up your chimney and condensing. It will be even worse if you have a gas fire that vents up the chimney. Go out and look at the other end terrace houses and you'll see a damp line up the bricks where the chimney runs. I really don't know what the other posters are banging on about.

 

[Possel]

Heather. Having read the above posts, I'll add my view.

Some of the above might actually appear to work for a time - if you are lucky, a long time, but the issues are much deeper. Your house, built in 1910, was most probably built with lime mortar and no DPC. If it was an early use of cement then ignore the rest of this!

They didn't live in perpetual dampness because they knew what they were doing (usually). The design of a old house is that it is "breathable". The walls allowed the flow of moisture through them - outside it was taken away by the wind, assuming there were no plants growing up the wall. Inside, there were enough draughts to carry it away from the floor and ceiling and out of the house.

If (as too many people do) you try to tackle damp problems in an old house by throwing new solutions at it, all you do is to address the symptoms and move the problems around, without ever addressing the actual causes of damp. A modern house is a dry, sealed box - something that an old house wasn't meant to be, and trying to make it so can cause lots of issues.

Sadly, this advice is probably too late for you as you already have a DPC, and your house has lots of cement and modern plaster, which all holds the dampness in the walls when it is trying to get out. So the plaster on your chimney actually needs to be lime plaster which would allow dampness inside to escape. Hence I'd advise that your gable wall should be rendered with lime not cement based mortar, which would help that wall to breathe. You'd have to remove all the old stuff first if it is cement.

That's really helpful! I almost want to print it out and use as a bible!

Well, it's great advice if your house isn't made out of lime.

I was told back then was that if I do the DPC then that would solve everything...

That's how they make their money, and they have the entire country believing that a house isn't a house without a DPC. You even get Building Societies insisting on one when it is just not appropriate - at best a waste of money, at worst you are actually damaging your house.

My credentials are that (in the last year) I have proved how an old house dries out when all the causes of damp are tackled, without using any cement or gypsum plaster or any new-fangled modern techniques. All I have done is to tackle the sources of water ingress - slates, flashing, gutters, drain pipes, drains and the ground level above the internal floor level, plus the poor ventilation due to ivy and trees on the walls. See my blog at http://houseintheenchantedforest.blogspot.com/