Solid exterior wall, insulated plasterboard and damp issue


15 Jan 2020
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United Kingdom
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.



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I would hazard a guess that this is penetrating damp. Dot and dabbed insulated boards can cause mould issues, but I wouldn't expect it to appear like that
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Thanks for the reply, after speaking to a few people I think the bay window damp is an issue with the windows or roof.

It looks like a vent wasn't added to the chimney when that was capped off so I'm guessing that's causing the mould there!
Unfortunately, given that dot and dabbed insulated boards are a no-no, I think you would be best to rip it all back to brick and do it properly
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Unfortunately, given that dot and dabbed insulated boards are a no-no, I think you would be best to rip it all back to brick and do it properly

This was my original concern but getting mixed reports from builders and the forums some are saying dot and dab is is fine onto solid walls others not.
The issue is with warm wet air meeting cold wall and causing condensation, and then mould. You can dot and dab, but need to ensure that the entire perimeter of the board is a solid bed of adhesive, which a lot of people wouldn't.

If you take one board off and find that, you may be ok
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Think I'll take a board off and get someone out to have a look. Looks like my renovation costs may have just increased somewhat. Would this only be for the exterior walls or would you suggest the same for interior walls too?

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