We live in a 100+ year old stone house in Scotland. Most of the rooms are lined with lath and plaster however a newer extension seems to have internally rendered walls (doesn't sound like plaster when tapped?) In these rooms (one is the bathroom) we have an on-going problem with mould on the walls. I have installed an extractor fan and new windows have trickle vents but the problems persist. The walls are very cold to the touch in winter. I have checked externally for leaky gutters etc but all seems fine. Should I be thinking about dry-lining the walls? Or would this just mask the problem rather than fix it?
=============== The 'cheap and cheerful' solution is to line the walls with polystyrene sheet. This is sold in rolls like wallpaper and it's applied in the same way as wallpaper using a fungicidal paste. You can then put normal wallpaper over it. The only real disadvantage is that it's about 1/8" (3mm) thick and is slightly spongy which means that it bruises if you bump against it. It is actually quite effective - assuming that the mould is caused only by cold and poor ventilation.
The alternative solution is more heat and ventilation.
We cured the same problem in an old coach house in the west of scotland a few years ago by using the polystyrene rolls, along with ventilation and heating. Our current bathroom suffers some what but with heat and ventilation we can keep it at bay. We are still bath users(no shower) when running baths the cold water first then the hot (safe this way as well)lessens the amount of steam and condensation but the kids always seem to do it the otherway and we end up with the walls streaming. cyril
Assuming that the mould is due to normal condensation failing to evaporate away and that the cause is not due to excess damp IN the wall itself (rising up from the ground, if the bathroom is on the ground floor, and no damp proof course, for instance), then one solution which can work excellently is to (prep the wall first of course) stick on a kind of tile that is widely available.
They are made of plastic with a polystyrene backing and are about 30cm square. They simulate a 'genuine' 3x3 (or maybe 4x4) porcelain tile array. What is good about this is that it is quick, quite inexpensive, is fairly permanent, does the trick 100% and looks good (if done properly - not hard to do, and you exercise good taste when you go shopping for them).
I emphasise you use these plastic (with polystyrene backing) and NOT traditional 'cold' tiles (which would just make it easier to wipe away the condensation but would still, probably, grow mould esp. on the grouting).
In the room which isn't a bathroom you could try the polystryrene liner. Again quite cheap and easy. But with this you would need to paper on top.
Both products are widely available in DIY decorating shops.
These work because of the heat insulation properites of the 'shield' which is effectively what you would be applying to the wall. They present a warm surface to the moist air and thus condensation is far less likely to occur.
What ever solution you opt for, keep an eye out for condensation that lingers. The extraction fan you have is probably not causing enough air to pass close to the affected wall/s to make the condensation evaporate and the constantly damp wall naturally nurtures mould in that case.
Bleach (diluted) is quite effective at removing the mould and keeping it at bay but is not the answer as a permanent fix.
Black mould (the most likely kind of mould) is suspect as a health threat. ie not much is known about the effects this has on a person health (who breathes the spores to some extent).
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