Chimney Stack Damp & Hygroscopic salts

[Refurb_Rob]

Hello,

I'm seeking opinion on the most sure way of plastering/plaster-boarding a chimney stack that has both damp patches and hygroscopic salts. I have/will have ventilated this chimney stack as much as possible, but I believe it will continue to retain damp in the brickwork and thus always have a risk of damp patches coming through.

I live in a 2 bedroom 1900's terrace where I am currently converting my loft to add an extra bedroom. The chimney stack in the living room is plastered, but above it in the first floor bedroom and loft room the chimney stack currently has the brickwork exposed. The chimney stack has two separate chambers, one leading up to the top from the living room and one leading up to the top from the bedroom. Within the living room the plastered chimney wall is damp (21%) and has a stain on the wall. Within the bedroom the chimney brickwork is damp to the left side (19.5%). Within the loft room, hygroscopic salts are coming through the brickwork and it is damp also to the left side (19.5%).

The chamber leading up from living room is currently fully ventilated with a vent at the top, in the future I may add a wood burner in the living room to get some heat passing through. I have recently unblocked the chamber leading up from the bedroom, though it is currently capped at the top I intend to have it unblocked & add an airbrick to this chamber in the loft room. So from a ventilation perspective I think that would be everything possible.

I would like to replaster/board the chimney in both the bedroom and loft room in such a way that I do not have damp patches come through the finish in the future. My thinking was to:

• Apply a salt neutraliser to the chimney brickwork in bedroom, loft room and living room (as I understand it can work through plaster).
• Apply a damp proof plaster such as Dryzone Damp Resistant Renovation Plaster to the exposed brickwork in the bedroom and loft room. This would hopefully keep the salts/damp contained whilst allowing the bricks to breathe through the plaster.
• Add a moisture resistant plasterboard over the damp proof plaster, using batons to fix to the wall & a DPC moisture barrier behind each baton. This would create an airgap between the damp proof plaster and the plasterboard which I would ensure had a internal ventilation grill so air could circulate. This would hopefully give me a way to hide any damp whilst also managing it with ventilation.

I would be keen to hear if anyone had opinion on this approach? Or any suggestions on best quality materials. Many Thanks

 

[blup]

Continue to ventilate the chimney and add studs plus plasterboard. The studs can be isolated from the damp by plastic packers and plugs.

 

[opps]

I think, I vaguely remember someone here using expanding foam to fix the plasterboard over the salty brickwork.

Not something I have ever tried though.