New plaster, few weeks later black mould

Discussion in 'Plastering and Rendering' started by alpeshk, 11 Nov 2021.

  1. alpeshk

    alpeshk

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    End of terrace house. Chimneys were removed.
    Plaster boards were stuck on the old plaster or brick work.
    Skimmed.
    The bottom two rooms have developed black mould looking spots.
    The up stair rooms are okay so far.

    Is this real damp coming through the wall?
    Lack of air circulation during the curing time? Can this be cleaned up using bleach?

    See photos attached.
     

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  2. Mr Chibs

    Mr Chibs

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    Did you have windows open upstairs?

    Id assume it’s a ventilation issue.

    Normally weak bleach/water solution would be used to remove mould spots.
    Don’t think I’ve tried it on plaster, test first in a small patch.
     
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  4. Godwasaplasterer

    Godwasaplasterer

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    normally this time of year because of the extended drying time of the pb adhesive. wipe it off with a bit of bleach and get a dehumidifier in the room to help it dry out.
     
  5. RonnieE

    RonnieE

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    Do NOT use bleach. This is a common misconception.

    Also, when you are in that room, wear a mask for your own safety along with other PPE.

    Bleach can actually make the problem worse whilst superficially making it look better. Focus on the cause of this (which I will explain).

    Mould needs the following conditions to grow, many of which are related:

    1) Moisture - wet plaster provides that
    2) A medium to grow on - plaster is very mould friendly
    3) Lack of airflow - is the room ventilated
    4) Lack of direct sunlight - common at this time of year
    5) Lack of disturbance - I expect it has had this, unless you have been wiping or cleaning it
    6) The right temperature - inside a house provides this easily

    The key thing is to get the room dry, without moisture / water mould will not grow. Good ventilation or a dehumidifier would certainly help.

    Your comment about 'chimneys were removed' - can you please clarify what you mean by this as it could have contributed to the issue (removing some ventilation)

    There are antimicrobial products for dealing with mould, or, professional services if the problem is bad enough.
     
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