Blocked up fireplace - paint peeling

About a year ago, we blocked up a fireplace with thermalite blocks. We then plastered over it (a coat of onecoat followed by a thin coat of multifinish).
The whole room was skimmed at the same time, and subsequently painted.
We didn't put an air brick in, because the chimney has been removed. This is a single fireplace stack, the chimney has been taken down to below roof tiles, and the fireplace blocked up.
All has been well up until now - I've just noticed that the paint (plain emulsion) is peeling in two patches, about 6"x6" each, just above the skirting, and just to the sides of where the blocked up opening is. The paint isn't peeling over the blocked up area, just at the two lower corners.
    _________________     |        |     | old opening    |     | blocked up    | peel |        |peel ________|        |___________
The room is kept nice and warm, and is reasonably well ventilated.
Any thoughts as to the cause and remedy? Condensation in the stack? If so, why in those two spots?
TIA
--
Grunff


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Just a guess but depending on how many bricks there are before resting on the ground/foundations and how good your damp course is it could be Rising damp? Several people have said to me rising damp can travel up about 3 foot / 1 Metre
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Chris Vowles wrote:

Yes, but why in just those two spots?
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Grunff


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I really wouldn't know, others might be able to suggest, If the fireplace is on an outside wall instead a party wall then it could be penetrating damp from outside ?, but if it is a party wall then I suspect it is rising damp?, if the fireplace was in use as a working fire providing heat before it was blocked up then perhaps the heat stopped the damp from showing ?
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Chris Vowles wrote:

I really doubt it - it is an outside wall, but that section is effectively double skinned, because it's the chimney breast. If it was penetrating, you'd be far more likely to get it on the walls either side of the chimney breast, which are single thickness.
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Not sure if you have got this sorted yet but a reply anyway.
God knows why only those two spots are coming through. It could be rising damp, which will come up to about a metre, but I doubt it, although if the hearth is of a concrete slab just laided on earth then it would be more likely.
I suspect it will be some sort of condensation. My rule is never to have a void that is not ventilated. Usually, it is asking for trouble.
One thought, but a bit of a long shot - are there any electrical sockets along the breast? If so, check them thoroughly, especially for rust if metal boxed. If so, you could try putting the sockets in plastic boxes. It is highly unlikely, but there could be some tiny current leaking and the fact that the blocks and bricks are different materials could be causing some form of moisture trap, in the same way as those old DPC systems used to work, where a small current was passed along the mortar course.
In fact, I recall there was a DPC system that used some form of ceramic/pot inserts placed into the brick every few feet that were supposed to wick moisture away from the surrounding brick and let it run out and down the wall. Again, the blocks could be performing some similar function, though I have never heard of it and it would beg the question of where the moisture was coming from.
You don't happen to run a portable Calor gas heater in the room, do you?
HTH Rob
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Kalico wrote:

No, not yet.

It is just a slab.

No sockets.

No way ;-)
It's got one big rad, and that's it.
One thing we've been thinking - when I blocked up the fireplace, the surrounding brickwork + plaster was deeply impregnated with oily tar. Could it be that this tar has slowly accumulated at the bottom of each side of the blocked up hole, and resulted in the paint lifting? Dunno. Maybe.
--
Grunff


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It the places it is coming through are roughly in line with the joint between the old brick and the newer blocks, then it is definitely something coming through because of this joint.
It could be the tar you suggest. Moisture will always wick to the driest/warmest area it can find. Your room in this case.
Not sure why you didn't remove the oily tar but this sounds like it could be your problem.
If all else fails, it looks like you're going to have to open it up again.
Rob
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Kalico wrote:

We removed as much as possible without rebuilding the surrounding brickwork. We PVAed what was left very thoroughly.

Yes, wouldn't be a huge job, so may end up doing that.
Thanks for your thoughts.
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something
could be

again.
Be sure to let the group (or me at least) know what you find. Good luck
Rob
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