New Plaster and small damp looking stain

3 Jun 2016
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United Kingdom

I've had a chimney hole filled in and the breast re-skimmed with pva and a rubber mesh underneath for strength. The old plaster was cracked and un-even.

Anyway my question is that there is a small patch on the plaster that after two weeks still looks damp but to be honest I've had a low powered heater blower on it and it's made no difference and other than feeling cold like the rest of the plaster it doesn't feel damp. So I don't know if it is damp or not. There is also a smaller spot on the other side.

Prior to plastering I dug out the hearth and the earth underneath was totally dry as was the inside of the chimney that could be accessed. The house is 1930 with solid walls but on the other side at the spot in question the outside bricks looks fine as does the mortar. Also there is no water coming down the chimney.

I tried giving the spot a very slight sanding and this hasn't helped.

The only thing I can think is that it is damp but god know how, or the wall paper paste which was holding the old paper on (and it was old) has somehow seeped in to the plaster!

Thoughts ?
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Demonic possession? Do you hear a squeaky voice telling Mary Anne to walk away from the white light?

Anywho, if it a ground floor chimney breast, shouldn't it have an air vent?

My advice as a decorator, would be to paint over it (with diluted emulsion) and monitor it
Yeah I removed hearth so it now vents under the suspended floor.
Fair play, as I said just paint over it and see what happens. I have encountered similar spots in the past and 90% of the time they have been fine. I have no idea why they occurred in the first place though.

Good luck.
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Yeah doesn't seem to get bigger or smaller now, not a clue what it is.
I'd suggest something is definitely behind that introducing cold air behind.

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