dark patches on attic chimney wall

Discussion in 'Plastering and Rendering' started by Hoyle23, 2 Mar 2017.

  1. Hoyle23

    Hoyle23

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    Hello,


    I have had an on going problem with darks marks that won't seem to go away. These marks are not wet, greasy or even colder than the rest of the wall, you can simply just see them. They were improving and going away but have recently appeared again (Not after rain, just generally cold weather). The never grow or change in size or appear any darker than they originally did but they have just reappeared in the same place. The area underneath and to the left of the beam is plasterboard, to the right is the chimney breast.


    We have had various work completed.

    :-This started off with having the wall taken back to brick with a salt neutralizer adding to the brick and left to dry overnight. A plaster coat applying to the area that was stripped back to brick and then a skim coat applying to the chimney wall and plasterboard area connected to the chimney wall.

    :- We have had the chimney repointed, chimney cowl checked and confirmed there is no problems, lead flashings and underfelt completely redone around the chimney. This appeared to solve the problem but it has shown again in the exact same place. (I have had 5 separate roofers check the work who have all said how well the work has been completed and they can't see any problems.)


    Does anyone have any idea what this could be? (a leak still, condensation, salts somehow still (Despite the salt neutralizer).


    Any advice or even guesses would be appreciated.


    Please see below pictures.

    Original - 2 weeks later - 3 weeks later - 4 weeks later - 4 and a half weeks later

    Original.jpg 2 weeks later.jpg 3 weeks later.jpg 4 weeks later.jpg 4 and a half weeks later.jpg

    Thanks,

    Andrew.
     
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  3. stevethespreader

    stevethespreader

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    Is it an outside wall? Is it solid? What undercoat was used? Are you sure it's not wet? As the bricks are ghosting and the plasterboard right next to it looks wet how long ago was it plastered?
     
  4. chris1982

    chris1982

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    I am no expert, but had a few problems with unused chimneys before. If I read your post correclty, you got the wall replastered before the chimney was repointed and the flashing redressed? If so, between the jobs the new plaster could have soaked up moisture and along with it soot and perhaps salts from the chimney, which might show now. I think a SBR slurry followed by a sand and cement scratch coat ahead of applying plaster would have been better in stopping soot and salts oozing from the chimney. That's at least what seems to have remedied the problem we had (and I used a "renovating plaster" that was lime based).
    Another potential issue you might have, and we had, is the chimney lacking a DPC. Out of five roofers I had looking at it, only one spotted this. He then quoted to rebuild the chimney stack - which I declined. Instead I sprayed the outside of the stack with a waterproofer.
     
  5. vinn

    vinn

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    You need to post pics of a larger context in the room - showing as much of that wall as possible.
    Pics of the other side of the wall will also help.
    And pics of any roof stack?
    Is there an access trap to see into the ceiling soffit?

    Where does that door lead to?


    Its not clear on my monitor but does the chimney breast project into the room?
    Is it a full c/breast from the ground floor up to a roof stack?
    Have the flues in the chimney been swept?
    Are any of the fireplaces being used - gas or solid fuel?
    Are any fireplaces blocked off?
     
  6. As Chris says, there's no DPC in the chimney. You need to drill and inject a silcone dpc into the mortar borth horizontal and the pers as it goes down the roof line. And a brick waterproofer will double the effectiveness. Waterproofers such as Ronseal have a limited life, hence the belt and braces approach - you don't want to have to do it twice.
     
    Last edited by a moderator: 3 Mar 2017
  7. vinn

    vinn

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    The OP makes no mention of a "DPC" - present or absent.
    I have never seen a drilled & injected "DPC" in a stack - anyway, its an absurdity to suggest such a procedure without seeing the stack.

    Neither will the "waterproofer" remedy fly, once again the stack is unseen, & the OP has already said that its been re-pointed.

    Given the information we have to work with, the most likely possibilities are in the first pic: its a back gutter problem and/or a non-vented flue(s) problem.

    As for the 5 roofers business: what next - six Geese a-laying?
     
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  9. Nige F

    Nige F

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    One Vinn a ranting.
     
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  10. Hoyle23

    Hoyle23

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    Thanks for the replies everyone.

    Just to explain a bit more, the first picture is before the repair work on the roof and then subsequent ones are after the roof repairs. We don't want to use any waterproofing product as we have been advised against this due to the age of the property (Solid wall house built in approximately 1900).


    The ghosting that appears on the first picture is before the chimney/roof repair work. I'm not sure what undercoat was used and I can't be sure there isn't still a leak, I am going by touch/feel and it doesn't feel any different to other parts of the same wall. It feels very cold but completely dry but this isn't surprising I don't think as it's the only external wall in the room.
    :-Sorry, I have seen the pics of the roof stack but don't have any on this computer. The other side of the wall is the inside of the chimney breast.
    :-No access to the ceiling soffit.
    :-The door is a cupboard with what looks like a piece of chipboard for the top of it that is completely dry and shows no signs of ever being wet/damp.
    :-Yes, it projects into the room.
    :- I don't believe the flues in the chimney have been swept.
    :- The fireplaces are not being used and are blocked off. In the downstairs room there is an electric fireplace mounted to the wall with the wires going into the wall/chimney behind.


    Hope that answers a few questions and if anyone has any clearer ideas it would be appreciated.

    Thanks,
    Andrew.
     
  11. stevethespreader

    stevethespreader

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    If that was my wall I would take it back to brick "again" the plastering is shocking anyway
     
  12. Gossamer

    Gossamer

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    I had similar in my ~100 year old house front bedroom and lounge. Last year I did the following, in order:
    1. Hacked off the affected plaster and had it replastered using a salt retardant additive.
    2. Had the chimney flashing redone as it was suspect.
    3. Had the chimney stack coated in a waterproof 'paint'.
    4. Had the chimney swept.
    I've also since installed a woodburner so the chimney is now back in use with a flue.

    Time will tell.....
     
  13. vinn

    vinn

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    I dont understand why you cant show pics of the stack and the other side of the c/breast?
    And, as I asked above, pics of the whole c/breast wall will definitely help?

    Hack off back to brick as suggested above and also remove any damp stained plasterboard. But dont yet take any remedial measures.
    Open up all blocked off fireplaces and sweep the flues - when covering a fireplace opening a vent must be inserted, and an appropriate ventilation terminal inserted in the chimney pot.

    What do you intend to do about examining the back gutter - nowadays, many roofers will take pics of the stack before & after any work.
    Pics are best for any post-mortems.
    Close up pics of the back gutter & stack would help.
     
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