I've been off air for so long that my 6MB mailbox is
almost full of important missives screaming for my
attention - but with virtually no time to look at them
I'm tempted just to delete them and start again.

However, I had no resistance to this one.

 --- Michael Edison wrote:
> So how sure is anyone that the electronic moisture
> meter readings mean anything on brick? I am
> convinced that they are almost worthless on terra
> cotta, useful on sandstone.

Personally, I think that an electronic moisture meter
reading on any sort of masonry means:

1) there is moisture present
or
2) there are soluble salts present which mean that
there is at least a small amount of moisture present
or
3) there is moisture and salts present

In the instance being discussed, if there is rising
damp, then there are almost certainly some soluble
salts, which means that the wall will never dry out
until the source of the rising damp is removed, and
depending on the quantity of soluble salts present,
some or all of the soluble salts removed.

I love electronic moisture meters.  They can tell me
that a wall is (1) or (2) or (3).  Useful if the wall
has recently been repaired, particularly if that
involved replastering and repainting to hide all the
evidence of deterioration.  Otherwise, I can probably
see the evidence of rising damp ... which means that
the moisture meter isn't a lot of good.

Now, when I started out in this game nearly 20 years
ago (and I've been waiting for ages to be able to say
that! NOT!), I used an old Speedy Moisture Content
Meter which used a ?carbide powder mixed with a sample
of dust extracted from the wall in a small pressure
vessel - the carbide powder reacted with the water in
the sample so that the amount of water could be
calculated from the amount of pressure generated.
That, combined with analyses for soluble salt content
(which could be done in an ad-hoc manner on site by
shaking the drill dust in water and measuring the
conductivity of the sample, then calculating from
standard curves prepared previously in the lab ...
just relied on assumptions about the identity of the
soluble salts), was about as good as it gets when
you're out of site.  Only trouble is that you needed
to drill relatively large holes for sampling.

If there was enough demand, I have no doubt that
neutron devices as used in the mineral processing
industry could be developed for this purpose that
would require no destructive sampling ... but we'd
spend all our time calibrating them!!  For what
purpose!

Anyway, time I went home to bed.

Good to see you're all still busy firing off
contributions - and good to be back on board, albeit
only very briefly.

Cheers
david

http://www.sold.com.au - SOLD.com.au Auctions
- 1,000s of Bargains!

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