Strangely isolated damp problem...

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We have a longstanding issue with a strange re-occurrence of damp spots either side of a chimney breast in an internal party wall of our semi detached Victorian house.

One patch about a foot square just above the skirting, another on the other side about 6" square about 18" higher, and a small patch at the corner of the chimney breast at floor level.

I've dealt with bigger issues before and have an understanding of damp proof courses, condensation, ventilation etc., I cleared the base of chimney breast of soot deposits when upgrading the fire from coal to gas, both areas have been re-plastered at some stage and treated with damp proofing paint prior to papering.
There is no obvious damp, no horror film photos of mould etc., and it takes many months, a year or more before the paper starts to part company with the wall and for dark patches to appear but they always come back.

It transpires that our adjoining neighbour has similar issues and like us are scratching their heads.

Any suggestions/advice welcomed?
 
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Posting pics showing the whole back wall/party wall & chimney breast - floor to ceiling will help?
Pics of the chimney stack will also help?

Is the fireplace in the room above an open fireplace or has it been blocked off?
Does the neighbour have any blocked off fireplaces?
Is your floor suspended or solid?
Have you ever been into the loft space just below the roof?

Typically: "re-plastered" tends to mean gypsum plaster - bad, not lime and sand render - good.
Applications sold as "damp proofing paint" are mostly a waste of money, and can sometimes cause further problems.
 
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Aren’t chimneys prone to salt build up?

That then sucks moisture from the room much more easily than anything else; hence the spots.

You could hack it back to brick, neutralise the salts and then lime lender?
 
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Posting pics showing the whole back wall/party wall & chimney breast - floor to ceiling will help?
There is nothing to see, other than perfectly dry sound walls apart from the patches.
Pics of the chimney stack will also help?
On the roof?
Is the fireplace in the room above an open fireplace or has it been blocked off?
There's not a fireplace in the room above. We moved in 35 years ago and there wasn't one then.
Does the neighbour have any blocked off fireplaces?
They have a new log burner downstairs.
Is your floor suspended or solid?
Suspended.
Have you ever been into the loft space just below the roof?
Yes.
Typically: "re-plastered" tends to mean gypsum plaster - bad, not lime and sand render - good.
Applications sold as "damp proofing paint" are mostly a waste of money, and can sometimes cause further problems.
Damproofing paint has worked well on the area at the corner of the stack.

Answers within above...
 
Joined
30 Sep 2009
Messages
8
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Location
Essex
Country
United Kingdom
Aren’t chimneys prone to salt build up?

That then sucks moisture from the room much more easily than anything else; hence the spots.

You could hack it back to brick, neutralise the salts and then lime lender?
There is some evidence of damp at the rear corner of the stack where it joins the walls either side. To put it into perspective the room was decorated and wallpapered 4-5 years ago and has only just started to present the dark patches.

The wall to one side may be lath and plaster.
 
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