Condensation Problem

[Stephen Jones]

I have a problem with condensation on a solid ground floor out side wall. The wall has been treated with something like tar behind the plaster and been painted with a gloss paint, the plaster looks fine but is damp in little unconnected patches. Over night you get condensation on the bottom two foot of the wall particularly in a corner alcove clothes cupboard. What you see is water droplets on the paint and a musty clothes in the cupboard. I have thought of sticking the silver backed plaster board to the walls but wondered if sticking the polystrene type wallpaer to the walls would increase the insulation and be easier, someone is sleeping in the room so major work is difficult. Any help would be appreciated.

Steve

[Christian McArdle]

25mm celotex at the back of the built in cupboard, covered with plasterboard for the sake of appearance. Ensure the cupboard is ventilated. A few holes in the top (or wherever they can't be seen would be good).

Christian.

[IMM]

Remove the gloss paint. This prevents any vapour from moving in and out of the plaster. Then install Celotex and plasterboard over.

[Peter Taylor]

IMM wrote

And what good will that do?

[IMM]

The gloss paint may trap water vapour and give damp patches.

[Peter Taylor]

IMM wrote

Rubbish. How can the vapour get trapped behind the paint? It would have to pass through the paint film first to get to the other side, so why can't it get back again?

[IMM]

If a real damp problem from outside it gets trapped. Vapour can also come from outside too.

[Peter Taylor]

How often would that happen? There will only be sufficient vapour pressure to create a reverse flow when the temperature and humidity externally are considerably higher than internally. You might get that max 1 or 2 days a year, when it's very hot and sticky and with the aircon on full. Not a normal domestic situation by any means. Basically, for this discussion it ain't gonna happen.

Besides, even if it were to happen, didn't the OP say there was "something like tar" (presumably Synthaprufe) on the wall surface behind the plaster? Wouldn't that prevent any vapour/moisture from entering? You seem to have ignored this or maybe, as usual, you didn't read it properly.

Removing the paint would go completely against proper principles of condensation control. It would allow even more vapour to permeate the wall and create interstitial condensation and even worse damp patches on the plaster surface. Isn't that what the OP was complaining about to start with, or didn't you read that either? You simply don't understand condensation, and your misguided advice could lead innocent, decent people into making expensive mistakes. If I did that I would quite rightly be sued.

Peter

[IMM]

message

This is clearly an insulation problem. The gloss paint does not help at all if there is no insulation. The gloss does act as a vapour barrier, but the damp is still there. It could be trapped by the glass too.