Hygroscopic Salts in Plaster - Treat and Re-plaster Method

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Hi, after a bit of advice please.

Having had numerous roofers investigate what looks like a damp patch on an upstairs wall adjacent to an old chimney stack, non of whom can identify any specific roof, guttering or mortar damage, it has been suggested that the patch could be the result of an old leak that has contaminated the plaster with salts and/or salts penetrating from the old chimney stack. This seems to make some sense.

During periods of high humidity the patch gets darker and over time has developed a yellowish tinge but has never developed mould. The adjacent room (other side of the stack) is worse, with blown plaster in an airing cupboard and lots of efflorescence (this room happens to be the bathroom).

My question is, assuming this is the issue, how best to rectify it?

Options I have been given all involve the removal of the old plaster and then…

1-add salt neutraliser to brickwork, sand and cement mix render including waterproofing additive & salt retardant additive, then skim.

2-tanking slurry, sand and cement mix render including waterproofing additive & salt retardant additive, then skim.

3-tanking slurry, fix moisture boards, then skim.

Obviously want to get this right so just after opinions on the above options and whether I should go moisture boards or the render route?

Thanks in advance.
 
Hi. We always dry line chimney breasts. Either treated roofing battens and standard 12.5m boards or if the damp is extensive Permaguard PB2 membrane then dot and dab standard 12.5m plasterboards. If you can't fix it...isolate it.
 
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