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Hygroscopic salt(?) stain

Discussion in 'Plastering and Rendering' started by reubin78, 30 Oct 2019.

  1. reubin78

    reubin78

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    Hi,

    Looking for advice with a Hygroscopic salt(?) stain. It does not seem to get worse/larger but reappears after decorating (painting).

    The facts:

    Property is brick Victoria-era (mid 1880s)

    There are no issues with flaking paintwork, white fluff/salt tide marks - just a reappearing stain. Affected area feels colder than surrounding area (this time of year)

    The affected area of wall is between a bedroom and the old kitchen chimney. It is mid/top section of wall.

    The stains are in the bedroom.

    The chimney is only used for the kitchen/hob extractor fan which has a flue that is directed out of a vent (side of chimney). The bottom of the chimney is therefore effectively sealed. The chimney has a wide opening in the side which our range cooker sits in.

    The original chimney was dropped so that the roof could be fully tiled. The lowered chimney is capped and has a black flue/breather (and cap) that stands taller than the roof. We are happy the roof, brickwork, etc is watertight

    There is no other ventilation for the chimney.

    After the chimney was dropped, we waited before decorating. The repainted walls seemed fine but the "stained" area slowly reappeared (over a couple of years)

    My wife is currently redecorating and the repainted areas have soon shown the "stained" area. (Possibly not helped by to time of year - damp air, etc)


    The solution: (the bit where I need help!!)

    I had assumed it was to do with ventilation (or lack of) and was set to fit an air brick into the external face of the chimney. Is it worth installing one?

    My neighbour has suggested it is hygroscopic salt and says the only way to resolve is affected plaster off.

    Is this the only solution? Is there a way of treating the plastered wall to form a seal - as far as stopping the "stain"? I've done a quick Google and there seem to be salt neutralises and various paints but not sure if these are for adding to a plaster mix or maybe just gimmicks.

    Not looking to cut corners but equally trying to avoid a big job where a smaller fix is possible.
     
    Last edited: 30 Oct 2019
  2. foxhole

    foxhole

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    With no ventilation the chimney will takes years to dry out if ever.
     
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  4. reubin78

    reubin78

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    Thanks - that's what I figured. The ventilation should help rather than hinder.

    The remaining question what we can do inside. Namely, is there a way of stopping the stain (i.e. is there a suitable product that works?!?)
     
  5. KenGMac

    KenGMac

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    reubin78, good evening.

    Totally agree with foxhole above.

    If you consider it, there is a flue, but? it is sealed at the base, result, no through ventilation / condensation / dampness / Etc.

    If you can fit an external vent, not at the base but a wee bit above the base of the flue, if you fit the vent at the base it may get blocked up by crap falling from the inner surfaces of the old flue.

    As for lotions and potions designed to "eliminate" salt staining??? Nuff said?

    Ken.
     
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  7. bobasd

    bobasd

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    as above suggestions.
    OP, if you go in the loft and remove the flue capping it will help a bit.
    the flue should have been swept when it became redundant.

    hack off the stained plaster and for 300mm around the stain at a min.
    then render with a 3:1 sand and lime mix or, say a remedial plaster such as Limelite.
     
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