Solid exterior wall, insulated plasterboard and damp issue

Discussion in 'Builders' Talk' started by OJD, Jan 15, 2020.

  1. OJD

    OJD New Member

    I’ve recently taken ownership of a Victorian house that’s currently inhabitable but the previous owner had started renovation work. All of the solid walls have had their plaster removed, been taken back to brick and new plasterboard has been put up (around 14-18 months ago) but we have found 2 damp patches.

    The first damp problem is underneath a bay window in the lounge. All the exterior walls have been plaster boarded with insulated plasterboards that have been dot and dabbed, which you can see in the picture with the black mildew. The previous owner has left a stack of boards in the house too so you can see what were used by the builders.

    The second bit of damp I have found is in the dinning room. The previous owners bricked up the fireplace and plaster boarded with insulated board that was also dot and dabbed but in this room the damp spot has a green powdery mould on it which you can see in the second picture.

    I know that both of these issues need to be addressed ASAP but what could be causing the damp in each area? The rest of the plasterboard around the house is dry. My concern is that all of the exterior walls have been dot and dabbed with insulated boards and they may develop issues with damp over time meaning they’re all going to have to come down and be replaced.

    I should mention there hasn’t been any heating on in the house since September 2019 but I’ve now installed a thermostat and the heating has been set to 12 degrees to keep it dry until we start renovation work again.

  2. carl24bpool

    carl24bpool Active Member

    The bay window one is likely to be the bay roof (if it has a roof). Get up there and check for areas that are a likely cause. Most probably along the back somewhere.

    THe other issue could be a variety of things. You need to ascertain whether the damp is from above or below. Perhaps lift some boards next to the chimney and see if the walls below are damp. I have a similar issue which is rising damp from failed damp course on my chimney breast.
    OJD likes this.
  3. Mr Rusty

    Mr Rusty Screwfix Select

    read heritage house re solid walls and insulation

    The problem is internal insulation makes the wall itself colder. If condensation from interior gets to it you get condensation inside the wall.

    For the fireplace, my own experience is that bricks around fireplaces get loaded with salts as a result of reaction between building materials (principally lime) and combustion products. The salts are hygroscopic - they migrate to the surface easily through dabs and draw moisture out the air.

    Get the house warm and dry and see where you are, then make a decision.

    FWIW - I am with heritage house - I don't believe in "rising damp", and think by far the majority of "damp" is condensation in one form or another
    KIAB and OJD like this.
  4. OJD

    OJD New Member

    Thanks for the replies! Heating is on and getting everything dry and warmed up.

    The builder who did all the previous renovation work is going to come round and see me next week. I suspect no vent was put in the chimney after it was capped off and that's causing the green mould there.

    The bay window had new windows fitted about 12 months ago when it was down to brick, so I think something might be off there or there maybe a leak in the roof so will investigate over the weekend.

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