Discolouring and Smell behind false wall

Discussion in 'Builders' Talk' started by Matt_H, May 16, 2018.

  1. Matt_H

    Matt_H Member

    Our bedroom has got a false wall made from a sheet of board which hides the chimney breast.

    There are no vents into the gap behind the board.

    The back of the wardrobe has recently come off a little and I have noticed that the real chimney breast and back wall has become discoloured - it also smells. Please see the photos. The wall/chimney breast is covered with some polystyrene stuff that is discoloured.

    Is this just because there has been no air flowing through this small space...or is it something more sinister.

    I have now put in a vent through the false wall (see photo) - so there is now some air flowing through - is this enough or do I have to do anything else?


    Attached Files:

  2. Josh.91

    Josh.91 Member

    is that on a Pine End, or a Terraced Property? If the latter, leave it a few days & see if it dries out.
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  3. rogerk101

    rogerk101 Well-Known Member

    It sounds like you have a leak at the top of your chimney.
    Is your chimney still in use?
    If so, does it have anything that prevents rain from coming down the inside of the chimney?
    If not, was it capped off correctly?
    It could be that the capping is cracked or no longer waterproof.
    I have just had the same problem with my chimney and I had to climb up an paint on a few coats of water-based bitumastic sealing paint. The problem is now completely sorted, the walls are dry inside the house, and all the smells have disappeared.
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  4. Josh.91

    Josh.91 Member

    A correctly capped off Chimney should not need Bituminous paint surely. Never a permanent fix.
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  5. rogerk101

    rogerk101 Well-Known Member

    The capping on my chimneys were done long before I bought my house 12 years ago. They were capped with what appears to be quite a strong mortar mix, although onto what remains a mystery to me.

    There were several cracks in the mortar which I presumed to be where the damp was coming from. I used a bituminous paint on it 12 years ago, but only put two coats on back then. I've now just redone it with 4 good thick coats, which will hopefully last more than 12 years.

    So, you're right that it's not a permanent fix like it would be if it were done with fibreglass or lead, but it's good enough for me. I'll be an old man by the time I need to redo it (assuming I'm still in the house and not in frail care), so I don't really see the need for a more permanent solution. Who knows, maybe there won't be any oil left for my burner by then, and I'll have to reopen the chimneys up for a wood burning stove! I've already got more tree cuttings than I know what to do with, so heating my house with them seems like a good idea :)
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  6. Astramax

    Astramax Well-Known Member

    Get the chimney flashing checked.
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  7. Matt_H

    Matt_H Member

    Actually...the walls are all dry...maybe the stains are from old leaks.
  8. Josh.91

    Josh.91 Member

    Sounds like a good excuse to get a burner in! It's nothing less than an investment
    Matt_H likes this.
  9. Matt, it's probably a combination of the two - lack of ventilation of the actual flue, and also that section of wall being unventilated on the room side due to the cupboards.

    Your flue top should be capped - ie covered to prevent rain from getting in - but open to allow it to vent. Then you have a vent grill as you've just fitted in the room - although this will have limited effect if the top of the flue is fully capped -sealed - off.

    As said above, allow that wall area to breathe for a few days and see if the smell goes away.
    Matt_H likes this.
  10. rogerk101

    rogerk101 Well-Known Member

    If the chimney is capped in a completely water tight way, why would it still need to be ventilated? What would ventilation be trying to achieve?
    Removing damp? Why would there be damp if the capping was watertight?
    Removing smells? Why would there be smells if there was no damp?
    Anything else I'm missing?
    In fact I would probably suggest the opposite of ventilation ... I would propose filling it with insulation which could only improve the thermal insulation characteristics of that part of the house. The less the air flow, the better it's insulated.
    Matt_H likes this.
  11. What you say sounds reasonable, but is contrary to my understanding of the correct approach. The problem arises because the building's fabric is not fully moisture-tight so 'damp' air will slowly penetrate in to the chimney void and will condense out there as it's colder and has no ventilation. Expect long term issues.

    I can cite my own situation as a prime example - disused fireplace in the kitchen with stack now on an internal wall as the kitchen was an (old) extension. I removed the old cracked pot and fully capped off the top using slates and mortar, and also boarded the top of the opening and placed a light there as a feature - my thoughts were as yours; with no air getting in there won't be an issue... A regular sound from then on was bits of falling soot and s*** landing on this board, and stains forming on it...

    So I removed the capping, fitted a new pot with a 'pepperpot' on top (looks much better...) and the 'droppings' have ceased.
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