Clive Long,UK wrote:

Do you know what is the other side of the wall? (for example a bathroom,
a radiator, aquarium ;-) ?

On the other side is another narrow hallway with no furniture nor
radiator. The flats are "mirror image".

Oh well that eliminates some possibilities...

Well the wall I think is this "high carbon" material covered with
plaster skim. When I have drilled into it in the past it is a black
material that disintegrates when assaulted by a hammer drill. However,
the depth I am pushing in the probes of the Protimeter make me feel I
am only measuring conductance through damp plaster.

If the plaster is dry then they would be unlikely to make much
difference - however they will tend to make a slightly damp wall look
more damp than it is - think of the plaster as a medium value resistor
and the cinder block as a low value one wired in parallel with it.

The radiator is on the OPPOSITE wall to where the damp is - I did not
make this clear. Also all pipes are "surface mounted" on the skirting
and not leaking.

OK not that then

The reason I mentioned the radiator is that the Oxley book gives a
scenario where hot "moist" air from a radiator rises then moves across
the ceiling, cools, drops down the opposite wall, cools more until the
wall temperature is dew point and the moisture in the air condenses
into the porous plaster.

Would have to be in quite a damp environment I would have thought - if
the whole room is heated then the amount of dampness in the air to
circulate should not be that high unless there is an unventilated
adjacent shower room that is adding lots of moisture to the air.

But maybe if I lift the carpet and underlay, and some vinyl tiles. If
there is an obvious source of damp the underlay should be damp at this
point - and I can try to measure the dampness of the concrete screed.
Thoughts ???

May be worth doing... How far are you from "outside" at this point in
the building?

Some flooring materials (like the lime putty based stuff the use in some
places) can be quite hygroscopic - sucking water up from adjacent sources.

I have tried getting access to the neighbours property on 3 occasions.
He just says he doesn't have a damp problem and won't let me in to
measure. There are other issues around not getting access not related
to investigating damp. If I can get a solution to the "damp /
condensation" problem that then puts him in a position where he has to
be more co-operative - then that will be a satisfactory outcome. I
won't do anything that will deliberately cause a problem for him.

As mentioned above, routing of radiator pipes is not an issue as they
are all surface mounted.

I'm happy to pay a professional to cure the problem - but I need it
properly diagnosed. I get the impression that a lot of the
"Professionals" are quite the opposite - which is why I am performing
the initial investigation myself and I will be in a better position to
ask "why?".

I also suspect that many so called damp proofing "specialists" are
nothing of the sort - the whole industry seems to be somewhat
questionable in many cases (aided and abetted by the mortgage lenders /
surveyors as well!)

It strikes me that this would be an easy job to end up "fixing" without
ever finding the actual cause. This would only tend to hide the problem
though. For example the usual damp proofing company fix of hacking off
the plaster and replacing it with render containing a good amount of PVA
then skimming over, and pressure injecting a DPC along the base of the
wall would keep your side of the wall dry - might make the problem worse
(if there is one) on the other side though. If the problem really was
condensation then this could make your problem worse.

Nothing to stop you getting a few of the "damp experts" to give you
their view / estimate - you never know you may find one that knows what
they are doing.


--
Cheers,

John.

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