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
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?
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
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 ?
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.
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
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?
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.
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
If all else fails, it looks like you're going to have to open it up again.
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