www.ultimatehandyman.co.uk

So...there's a section of wall which is outside (the rest being internal to bathroom). There's a build-up of black mould on the external section. The other external wall of the same room was boarded over some time back (I believe with insulated plasterboard) and this seems to have stopped the condensation build-up on that wall.

So my question is...can the wall still having problems be boarded over with foil backed plasterboard (as opposed to insulated) as there is not much room as there is a door on the wall joining it so insulated would mean moving the door which isn't possible (because there isn't much room where the architrave should be). Hope that makes sense

Will the foil backed board stop the condensation build-up?

There's already a passive air vent fitted and an extractor fan in the bathroom next door.

Any ideas/suggestions how best to fix this? Thanks

Does your fan have an over-run ? Have you ever treated the mould ?

The fan does have an overrun yep.

Not that I know of...it's not my flat, I just do the maintenance for it. The mould is caused by condensation and just wipes off.

Foil backed board (otherwise known as duplex) is to stop vapour from passing through the board from the warm high humidity environment (your house) to a cold part of a wall build up, where there would be a risk/certainty of it condensing and causing "interstitial condensation". So in short answer to your query, no it won't make any difference to condensation on the decor face of the board. The only ways to stop that are :

1. Heat the room such that the wall warms up enough to be above the dew point (the point at which water vapour suspended in air condenses).
2. Insulate the wall to achieve same.
3. Reduce or better manage humidity within the room.

An upgrade to a decent extractor fan makes a world of a difference, especially if they have a reconcile feature, humidistat and over run. I upgraded mine and whereas before mold would build up every few months, now it's a small bit in the corner once a year

DIY_Johnny wrote:An upgrade to a decent extractor fan makes a world of a difference, especially if they have a trickle feature, humidistat and over run. I upgraded mine and whereas before mold would build up every few months, now it's a small bit in the corner once a year

typo:

Thanks...now to find a plasterer