damp coming through paint

[davidbrac]

Yep damp discussion again.
We have had a damp problem in a 22inch stone wall, and l have fixed the initial water problems problems - l hope

The wall is a 22inch stone that is lined inside with lath and plaster, and there is a cavity between the stone and lath.
The issue is that the chimney and wall have been soaked for a number of years and it will take a few years to get the stone wall back to its original dryness. However part of the wall in the dining room has stained onto the lath & plaster this includes a brown stain from the chimney, which keeps leaching through the decoration. I am confident that there is a draft at the back of the lath and plaster and that there is airflow from the under floor area to the loft.

I am now thinking of using damp proof foil on the wall to hold back the stains, Not on all of the wall just the section between the ceiling and picture rail. My thoughts are that the walls will still breath and that drying will continue, and that the foil will then hold back the staining which has made its way through stain block already.

Am l missing any other trick or issue?

 

[Zebra]

No idea about that product, but if you do that, you won't know whether the wall really is drying out, and whether you really have solved your initial water penetration problems. If it's a problem which will solve itself in time, as the wall dries out, can't you find a way to procrastine for a while? Find some other area that requires attention? KitKats help with procrastination, so I hear (although of course you have to call it constructive planning, or some such thing).
The alternative solution could be to lime plaster the wall, and limewash it. You can always limewash again over a stain, and the lime plaster won't be damaged in the least by a bit of moisture. Then if you really have solved the problems, and the wall dries out in a year or so, then you'll know, and be able to apply another coat of limewash and be happy that the wall is dry behind.
I can't imagine that that foil will stick very well to irregular stone in any case. Are you planning to remove the original lath and plaster in order to apply the stuff?

 

[88v8]

Foil on top of the plaster?
Soot staining is very hard to eliminate, it leaches back. I used Foildamp for that purpose in our previous house. Eventually it came unstuck but t'was after twenty years. See no harm in its use locally, as you say the rest of the wall will continue drying.

Ivor

 

[davidbrac]

yep bit misleading, I'm thinking of putting the foil paper on the lime plaster which is part of the lath & plaster wall, but just the top bit from the picture rail to the cornice, this is where the stain keeps coming through.

 

[88v8]

....this is where the stain keeps coming through.

Although eventually you may find that it starts appearing more widely, depending how well the drying process goes.
So I wouldn't put up any expensive wallpaper over it. Or if I did I'd make jolly sure I kept a spare roll somewhere. In our bedroom where the sootiness was manifest, I needed to do some local repapering after twenty years.
Oddly enough it was shortly before we sold the house.

Ivor

 

[MatthewC]

I've read this through several times and am still confused.

Is the leaching occurring where there is a cavity between lath and stone, or is there actually no cavity at that point? If there a cavity then there is the question of how did the leaching occur (leaking chimney?), but if that is the case then surely you could remove the discoloured plaster and re-plaster on new lath?

 

[davidbrac]

I've read this through several times and am still confused.

Is the leaching occurring where there is a cavity between lath and stone, or is there actually no cavity at that point? If there a cavity then there is the question of how did the leaching occur (leaking chimney?), but if that is the case then surely you could remove the discoloured plaster and re-plaster on new lath?

Yes there is a cavity. Yes removing the lime plaster and redoing it is an option, however this room has had a lot of work done on it, been decorated and l have moved on to some other projects. The removing of the lime will be delicate as there is some very ornate coving in this room. However if it is a problem that is still happening in 3-4 years time when l plan to change the fireplace in this room l will remove the plaster. For now l am looking to hold back the stain