avocado wrote:
Ed_Zep wrote:

I know that "damp meters" are much derided here as they don't
accurately say if there is damp in a wall or not but, as they *are*
used by surveyors, what level of dampness do they normally say is
something that's a problem or are they just a bunch of rip-off artists
and will say that the walls need doing if the thing beeps at all?

Thanks.

Damp meters are very accurate, it is the interpretion of their output
which is usually dodgy. The output from the meter together with a
visual examination of the situation is route to an accurate diagnosis.
If you get say five different damp companies you will get five
different opinions.

how can they be accurate if the area of probe in contact with the wall
is uncontrolled, as it is with 2 pointy bits on a rough surface.
how can they be accurate if building materials have resistance of their
own which adds to the current the damp meter measures
how can they be accurate if salts present in materials change the
conductivity of the water present and hence the readings

In wood yes. theyre fine, but on masonry theyre just not measuring
damp, theyre measuring resistance which depends on several factors.


NT