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I have stripped plaster from our dining room walls to reveal the brickwork in preparation for plasterboard and skimming. The room features one main exterior wall and an adjoining wall. Prior to removing the plaster, both had noticeable damp (though it was localised to the bottom corner of the wall, not along the walls length).

We have an osmosis wire running about 3 brick-course off the ground. However, this is the only room that is in direct contact with the ground soil. The floor is simply tiles onto compact soil. The osmosis wire works in the front room (which is above a cellar and thus not in direct contact with the soil), but it appears to fail in this corner. It is also the only wall with damp, all other interior walls, although also touching ground soil, remain dry enough.

Outside this exterior wall is a concrete path running down the side of the house. The house is a 2-up 2-down end terrace, approximately 1890s build. It has cavity walls, but the bottom of the cavity is likely filled with mortar rubble from degraded internal mortar pointing.

Most of the plaster that came off the walls was simply some form of thistle direct to the wall (not plasterboard/skim), but the lower half was plasterboard as this was renewed when the osmosis wire was installed. The plasterboard adhesive "dots" showed damp, presumably because of the moisture bridge they were creating.

I am about to re-plasterboard with polystyrene-backed plasterboard (only very thin, depth is an issue). I don't want to do this without first addressing the damp issue.

I am not a tradesman, but have growing DIY experience and understand a decent amount of the terminology. I'm also in the UK.

What solutions do I have available for damp proofing internally to stop damp attacking the plasterboard? I am open to all suggestions and will be researching to see if there is any plasterboard that is damp resistant.

I will be addressing the floor construction itself in a separate question if my internet searching doesn't yield many results.

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up vote 2 down vote accepted

Sounds like you just need a vapor barrier.

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+1 Indeed this is exactly what is required. Just had the plasterer round and he has a cement render that acts as a vapour barrier. – Adam Houldsworth Jun 10 '12 at 18:34

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