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Damp blocked off chimneys

Discussion in 'Building' started by robmorgan, 31 Jan 2015.

  1. robmorgan

    robmorgan

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    Hi all,

    Got a problem with the chimneys in our 1930's house. Both upstairs bedroom chimneys.

    Chimney 1 was already blocked off and vented when we moved in about 2 years ago. It had some signs of damp at the time which were gradually getting worse. The roof was shot anyway so we had that fully replaced. Both chimneys were repointed, reflashed and capped at the same time. We thought that would sort the damp but if anything it's accelerated and gotten a lot worse.

    Chimney 2 was open(ish) when we moved in. It had a poorly fitted victorian fireplace with concrete and bricks lumped in all around it so I can't imagine the airflow was great. We blocked this one in a couple of months ago. I always intended to vent it but kept putting it off (stupid I know) and now this one is starting to show signs of damp too (doh!)

    Been reading around and I gather this is a common issue in pre-60's houses due to the way the chimneys are lined. All seems a bit technical but I gather the issue is around salts allowing water to permeate through the bricks. Just went up in the loft and low and behold, there's salt on the back of the ceiling plasterboards and joists.

    So, what to do?! Yes I could/should/will vent chimney 2, but chimney 1 is really bad and getting worse and it ALREADY has a vent! So I can't be confident this will fully sort the problem on chimney 2 and I've no idea what to do about chimney 1 (already vented).

    As I say both chimneys have been completely overhauled (flashing/pointing) and are capped, so I'm really not sure what else to do about this short of reopening both the fireplaces! But then I gather once the water has got through you're stuffed, so maybe opening them back wouldn't help either?!

    Only thing I can think is it's mish mash of caps up there, think we've got a couple of pepperpots and the others are just curved roof tiles I think.

    Anyway, apologies for the war and peace, but just wanted to get all the details across in case anyone can shed some much needed wisdom on this!

    Thanks in advance,

    Rob



     
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  3. ree

    ree

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    Hi thanks for the pics so far but we need a context for the pics. Can you scan a rough sketch showing where the pics are, and any other info ref damp and c/stacks? Pics of the stacks, the stack flashing, and flaunching showing the terminals would really help?

    Here's a thing: its odds on that you will have to open any blocked fire openings - this is to enable the flues, all the flues, to be swept. Removing soot is essential for dealing with sulpherisation.

    The water stained timber in the pics - can you probe it to see if its merely stained or actually rotting?
     
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  4. robmorgan

    robmorgan

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    Thanks Ree.

    I'll post a sketch in a bit, but basically that pick is taken in the loft where the floor of the loft meets the chimney, right down in the corner of the eaves. The joist isn't rotting, and as you can see from the pics the water appears to have risen through it from below.

    Sorry, don't have a ladder long enough to reach the flashing (and I'm not great with heights!) but as I said the roof was completely replaced and the chimneys reflashed and repointed so I can't imagine there are any leaks. Certainly had to imagine both chimneys would have issues after a complete overhaul.

    I'm wondering now if blocking chimneys in a house of this age/design is simply a no-no and the only way forward is to reopen them.

    As I mentioned, chimney 1 has been blocked since we moved in 2 years ago and is getting very bad now even though it has a vent.

    Chimney 2 was open, I only closed it in a couple of months ago and now it's starting to show dampness around the coving in the upstairs bedroom. It was fine before so this suggests there's no leak as such it is just moisture caught in the chimney and condensing around the ceiling. Also the joists above chimney 2 are dry and no salt/residue which again suggests the moisture is coming from below but hasn't got to the loft yet as it has on chimney 1 which has been blocked much longer. I put a vent in yesterday but my gut feeling is it's not going to make a difference as the other one has always been vented and is getting worse by the day.

    If I opened them back up now should this stop the damp in its tracks? Or would it take a while to settle down? I suspect we're going to have to replaster the worst of the walls if not both of them.

    If I did open them back up I could get them swept as well. Would that make a big difference?

    Thanks again,

    Rob
     
  5. robmorgan

    robmorgan

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    Annoted photo showing blocked chimney 1, the worst one that's been blocked for at least 2 years and getting worse despite being vented at bottom.

     
  6. catlad

    catlad

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    Has the chimney breast been removed or is it on the outside of the house, how big is the chimney and what type of brick.
     
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  8. robmorgan

    robmorgan

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    No, chimney breasts haven't been removed. They're visible (jut out) on the side of the house. I think they serve the downstairs fireplaces (which are deeper) and the chimneys for the upstairs fireplaces are basically in the wall cavity?

    It's a detached house with 2 chimneys each serving 2 fireplaces. The 2 downstairs fireplaces are open the 2 upstairs ones are blocked.

    Openings downstairs are about 55cm wide.

    Not sure on the type of brick, fairly standard looking red bricks?
     
  9. catlad

    catlad

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    Without pictures its a bit like shooting in the dark, are the chimney's still used.
     
  10. ree

    ree

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    Thanks for the pic and the extra info.

    Nothing is going to "stop the damp in its tracks" given that its soaked into brickwork and plaster. The first thing to do is find the cause(s) of the damp.

    Roofers dont usually leave a "mish mash" of terminals on the stack. The next person to examine (or work on) the stack and its flashings should take before and after pics.

    You suspect sulpherisation, & it might be happening due to nothing worse than bad ventilation but there might also be water entering the flues thro the stack areas.

    As i said above, all flues must be swept. The flues can be opened for sweeping from outside, & the brickwork made good. Its also usually good practice to remove all contaminated plaster, and render back up in sand and cement.

    External chimney breasts are notoriously exposed to damp and flue gas cooling. Perhaps examine the pointing on your c/b's?
     
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  11. Joe Malone

    Joe Malone

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    Properly decommissioning the chimneys involves capping the stacks off or installing a top hat over the pot to prevent rainwater ingress. You must then ensure that a robust through flow of air is maintained from top to bottom by installing a double air brick at the external foot of the stack and another at the head of the stack, if you capped it of rather than installed a top hat. Chimney flues are lined with hygroscopic salts that will continue to draw moisture in to the masonry, which is why the ongoing air flow is required. When you say there is already a vent, where is it and what size is it? A common mistake is to vent the head of the chimney but not the foot.
     
  12. theprinceofdarkness

    theprinceofdarkness

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    I can't quite make up my mind where the gutter is. If the stack has been properly refurbished, then it should be watertight. So that leaves the external stack which could be letting water. Also if the stack is on the eaves side of the roof, the gutter should be kinked around the outstanding stack. There is not a leaking joint here, is there?, because there will be loads of joints! Or if the gutter is stopped/started here then the soakers/flashing must be made of properly into the gutter.
    Frank
     
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