1930's chimney damp - hydroscopic salts - can I line with moisture board?

Hi all.
Not been here for a few years, but glad to be back.....
We have just moved to our new house, a 1930's cavity, half rendered red brick house.
The chimney in the bedroom is wet, as is the dining room below. We are pretty sure its gyroscopic salts as the chimney has had a damp course, re-pointed and terracotta caps added over the last 3/4 years (by previous owner). The dining room fire was used daily up until the house fell empty last year.
Rather than re-plastering in lime and getting the very well embedded salts bleeding through again I was thinking we could dry line using moisture resistant plasterboard, with a small gap between the brick, to allow it to breath upwards in to the floor and roof voids.
Can I do this, or is it proper bodge it and I should just lime plaster?

Hygroscopic salts do appear on c/breasts and sometimes spread to the adjoining walls. If you post photos of the stained c/breasts, and photos of the exterior and c/stack it would help.

Typically & best practice, the flues are swept, and ventilated top & bottom, and all c/breast plaster is knocked off, and replaced with a 3:1 or 4:1 sand and lime mix with a cementitious skim eg. Limelite.

I had one of these a few years ago and took back to brick and floated it with dri coat and skimmed, not had any issues and patch hasn't reappeared

Cheers guys, that's what I'll do. Plaster is off already, gypsum patch was wet and loose, so took off the rest.
We are fitting stoves with liners so will dry out inside and keep vented.

Glad to be back!

Rob

"that's what i'll do" - what will you do?
You still dont know what the cause, or causes, of the stains might be?
How do you know if the previously claimed external work was actually done or done correctly?
"dry out inside" - dry out what?
If the stove has a liner then you do not vent the flue.

Cheers Vinn,
I'm going to:
Sweep chimneys
Allow the brick, where the gypsum was used to air out (patch above the fireplace, not uder the ceiling)
Allow the remaining lime plaster (which was hidden under blown vinyl) to dry out
Bond with SBR
Base coat of DRi-Coat
Finish skim of 1:3 lime & sand.
Leave to naturally dry out
Lined flues fitted (by fire man) in late Oct.

I'm based in North Bolton if you can recommend a reliable and trustworthy builder?
Rob