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Plastering & Rendering

Solid exterior wall, insulated plasterboard and damp problems

Anonymous user 09/03/2024 - 3.06 PM

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. You can use the links below to see the pictures I've posted of the problems on another forum: https://www.plasterersforum.com/attachments/bay-window-jpg.43926/ https://www.plasterersforum.com/attachments/fireplace-jpg.43927/ https://www.plasterersforum.com/attachments/insulated-boards-jpg.43928/

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5 Answers

S.s pike plastering

Rating: 5 out of 5
Bristol
Hi probably the heating hasn’t helped but you will get cold spots if the dot and dab has been applied directly to the brick or stone work which in turn will cause condensation and black mould to appear on the plasterer!! I hope this helps and if you need any more help just ask Many thanks S.S.pike plastering
Answered15 January 2020
6

Anonymous user

Empty houses can get the mildew damp spots especially near windows or cold spots. If unsure, remove plasterboard and tank the walls with a sbr/cement slurry. After 5 days it may still look damp but is actually bone dry. Hope this helps
Answered15 January 2020
0

mjplastering

Rating: 5 out of 5
Bromyard
Hi, There can be a few reasons as to why this has happened . Firstly not all thermal plasterboards have a vapour barrier in between the plasterboard and insulation foam ,so firstly check that they have , if not all that's happening is the moisture created by heating is being trapped at the back of the board and where there are real cold spots it will continually soak the dabs that are behind the boards in the cold spot area that's why the rest of the house is dry .Windows and beneath them are always vulnerable to this as if the window isn't as thermally good as the boards that have been applied then that can create a cold spot plus around the windows water can penetrate around the frame if it hasn't been sealed properly. The outside walls around the areas where the damp is showing might have penetrative damp and will need to be repointed and might need a clear sealer applied on the brickwork concerned. Regards Mark MJplastering.
Answered16 January 2020
0

Anonymous user

I never dot dab insulated board straight on to walls I always frame it out first
Answered22 January 2020
0

C a lappin plastering

Rating: 4.9 out of 5
Northwich
Damp around the bay window derives from vacuum which draws cooler air and damp the black mould is a fungus this fungus can be cured however there must be mortar cracks externally - the same with the chimney. it should have been capped and not just covered up. For an in-depth examination call a plasterer or builder and check survey report for further reports
Answered22 January 2020
0