Damp in chinmeybreast after rain

17 May 2013
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United Kingdom
it's original Victorian. The one area of damp we're aware of is the chimney breast at floor level in the living room. it suddenly went damp in the recent rain, on the plaster either side of the fireplace from ground to knee height only. Since then it's spread around the sides of the bottom of the chimney breast to reach the main wall. Looking at the wall, the plaster around the wet patches is visibly swollen and the tiles in the sides of the fireplace cracked/burst so I am assuming this means it is a frequent occurrence.

I'm wondering if this very fast appearance of damp (it was dry when we moved in though the evidence was there) implies running water rather than a damp problem per se. The main wall has had injection treatment and doesn't appear damp.

Could it be as simple as water running down the chimney?
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I am sure someone more knowledgable will come along soon, but I had a similar problem in a Georgian house. There some water did run down the chimney, but capping (and venting the chimney) did not resolve it. It needed removing the plaster into which a lot of hygroscopic salts had migrated from the chimney's soot.

If you produce steam in the room, do you get the damp patches on the chimney breast, and only there? If so, you might need to remove the plaster.
Oh that is a good point, I had read that once the plaster gets saturated it will draw in water every time there is damp in the air i.e. it's ruined even if there is no external water source anymore?

It's clearly been doing this for some time for the plaster to be all bulgy even when dry so I imagine the offending parts need cutting back regardless, being sure the issue is resolved to avoid the same happening again is the problem?

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