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 Post subject: Damp on chimney breast
PostPosted: Wed Aug 18, 2010 2:50 pm 
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Hi all

I hope I can get some advice on 2 issues with damp on the chimney breasts in our house. I am totally unsure what to do and how to go about doing it! Our house was built approx 1890 and been living here for 18 months.

We have two chimney breasts, one in both of our bedrooms.

1) The chimney breast in our spare room (soon to be nursery) shows signs of dampness at the top of the chimney breast through moisture being seen. This mostly happens when weather conditions are wet, damp etc. It is moist to touch. I have put the damp meter to the breast and it goes wild!. The plaster at the top of the chimney breast is blown slightly. We also have brown marks on the ceiling coming away from the chimney breast, again these send the damp meter wild. I have treated the ceiling wall with stain block but the marks have come back through. The chimney stack was taken down before we moved in and I have had a roofer go up on the roof recently and everything is ok up there. There is no open fire for this chimney.

I am totally at a lost as to what is causing the plaster to be blown and the breast to show signs of dampness/moisture and for the brown marks to return.


2) The chimney breast in our bedroom was damp and we had the chimney stack taken down last December to hopefully eredicate further damp. We stripped the wallpaper off so wall is back to plaster and had a dehumidifier in the room for a few weeks to help. We are now looking to decorate the room and having just checked the wall for damp, again the wall sends the damp meter wild! I have had 2 roofers round and everything looks ok. We also have brown marks on the ceiling coming away from the chimney breast. There is no open fire for this chimney downstairs as it has been closed off.

I am not sure whether to have the plaster hacked off to bare brick and allow the wall to dry out, or have the wall replastered over the plaster in its current state.

I appreciate its a bit of a long problem but I have no knowledge on these problems and a nagging wife!

Any help or advice would be very much appreciated

Thanks


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PostPosted: Wed Aug 18, 2010 3:15 pm 
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The plaster on chimney breasts is often contaminated with hygroscopic salts from the flue. These will attract condensation and cause dampness. The answer is to hack off the plaster and redo it with sand/cement with added waterproofer/salt retarder.


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PostPosted: Wed Aug 18, 2010 3:19 pm 
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Disagree Stuart, the most likely cause is the flashing (back gutter) and can be confirmed from checking the stack above the ceiling line (loft)

May also be a broken or missing tile.


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PostPosted: Wed Aug 18, 2010 3:30 pm 
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Thanks.

We do not have any chimney stacks on the roof as they have both been taken down. We have had roofers go up there to check for loose or broken tiles and everything seems fine.

Would it be wise to check the guttering around the house?


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PostPosted: Wed Aug 18, 2010 3:31 pm 
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The stack in the spare room has been taken down. Salts are quite a common problem on upper floor damp problems.


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PostPosted: Wed Aug 18, 2010 3:35 pm 
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Looks like hacking off the plaster might be the answer. Do you have any ideas on the brown marks on the ceiling that I have, or could they be linked to the chimney breast problem?


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PostPosted: Wed Aug 18, 2010 3:43 pm 
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Brown staining often comes from the flue. Hygroscopic salts are produced when burning fossil fuels and are deposited on the walls of the flue. Fires also produce water vapour which condenses at the cooler top of the flue and causes the salts etc to come through in to the plaster. This is only a guess at the cause of the problem.


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PostPosted: Wed Aug 18, 2010 3:51 pm 
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thanks for the advice will get plasterers round for quotes.


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PostPosted: Wed Aug 18, 2010 3:54 pm 
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So how long have the stacks been down and weathered.

If Stuarts theory were correct, then the breast would be stained but drying, how dry depends on the first question.

First thing I would do is fit a high and low level vents in the external wall of the chimney.


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PostPosted: Wed Aug 18, 2010 4:07 pm 
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The stack for the chimney in our bedroom has been down since last December, and the breast was taken back to plaster in March and damp meter readings are high. The breast in the other bedroom i am not too sure but it was down before we moved in which was 18 months ago. This breast is painted and shows signs of moisture and plaster is blown at top.


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PostPosted: Wed Aug 18, 2010 4:13 pm 
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Could be condensation from lack of air circulation, which is why I would get a high and low level air brick fitted outside.

The brown stain is obvious and common from chimney stacks, the wet and damp however is not, and the stack should be drying out by now, especially after 18months.


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PostPosted: Wed Aug 18, 2010 4:24 pm 
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Thanks for that. You say the brown stain is common for chimney stacks, i guess i could try it again with stain blocker, but that would be the 3rd attempt!!!


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PostPosted: Wed Aug 18, 2010 4:47 pm 
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qbscotty wrote:
Thanks for that. You say the brown stain is common for chimney stacks, i guess i could try it again with stain blocker, but that would be the 3rd attempt!!!


But if the breast is wet/damp, you'll be wasting your time, you need to get it dry first.


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PostPosted: Wed Aug 18, 2010 11:05 pm 
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I agree with Scruff, you need to ventilate the stacks top and bottom to get thro' flow of air.

S

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