DIY Doctor

Dot & Dab Insulated Plasterboard Condensation issue

Postby Reunat » Fri Jan 15, 2021 8:43 pm

Hi all,

Need some urgent advise thanks. I wanted to create a home office so had the outhouse in my garden fitted with 6 double power outlets then dot and dabbed directly to the brick with, on advice of the builder, Knauf 55mm XPS insulated plasterboard after applying PVA to the brickwork. The plasterboard was then skimmed.

Bitumen paint was applied to the concrete floor, then self leveling concrete then laminate laid.

Once all was dry, they painted initially with a mist coat of emulsion paint then with Dulux Easycare. This dried then immediately crumbled and flaked. They claimed it was the easycare being kept in the cold outhouse but believe it or not, this is the least of my worries!

I have noticed that the power outlets get quite a bit of condensation forming on and around them every night which is quite worrying (I have now turned off power to the outhouse at the fusebox).

They assured me when I initially noticed it, that it was the plaster drying but its been weeks since it was plastered and I am still noticing the condensation. I have read a little and suspect the vapour control layer has been broken by plasterboard being cut around the power outlets and not sealed.

Am I on the right track in anyones more experienced opinion, or is it a bigger issue? how do I rectify this?

Its getting colder and I have noticed rust forming on the brand new power outlet screw today!

I feel like the whole project has been a disaster and at this point, I just want to make it safe and avoid condensation ruining the whole structure.

Your feedback is appreciated.

Many Thanks
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Condensation on backbox
Reunat
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Postby stoneyboy » Sat Jan 16, 2021 5:16 pm

Hi reunat
Somehow you are going to have to surface mount the sockets and reinstate the vapour and insulation barrier in the cut outs. There is no recommended method of achieving this but you could try fitting plugs cut from the XPS but with a sizeable gap all round so you can embed the plug in silicone seal. Alternatively you could also try filling the cut-out with expanding foam but you will probably need to fit a temporary plate over the hole to contain the foam. It's a matter of try something and see if it works.
It may be worth lifting the edge laminate and see if there is damp below the underlay.
Regards S
stoneyboy
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Postby Reunat » Sat Jan 16, 2021 5:23 pm

Thanks @stoneboy. Thats really useful. The cables run between the outlets are mounted on the brickwork as well. Do I have to worry about them too and surface mount the runs? Or they are fine as they are?
Reunat
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Postby Reunat » Sat Jan 16, 2021 6:27 pm

Thanks so much @stoneboy

I spoke to the builder who clarified that the plasterboard is actually 27mm XPS and not 50mm I said before

Does that make a difference to the solution?

Also do the cable runs between the outlets need to come off the brickwork and laid at surface level or are they ok to remain behind the plasterboard on the brickwork?
Reunat
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Postby Reunat » Sat Jan 16, 2021 6:36 pm

Final question (sorry). Does the gap between the plasterboard and the flooring need to be filled / sealed because it is not. Just skirting boards on top.

If so, what should it be sealed with?

Just want to get this all done once and for all
Reunat
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Postby stoneyboy » Sat Jan 16, 2021 11:02 pm

Hi reinut
Cables - it there is enough length you could just feed them out of the cut-outs but they must be sealed in.
Thickness of the plasterboard is not relevant you will need to try and reform the vapour barrier in the cutouts.
Difficult to answer the question about the bottom gap - if water is running down the wall behind the insulation sealing the gap may make things worse.
Regards S
stoneyboy
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