Moisture Meters- The Key Facts
measurement and detection of moisture and the meters used is a complex
and important topic that is frequently misunderstood.
This article will outline the differences between the concepts of
‘moisture measurement’ and ‘moisture detection’ as well as explain the
most appropriate type of meter to use in different situations.
Moisture Measurement In Timber
most common material in which moisture content can be ‘measured’ by
using a moisture meter is timber. The typical tool used for this
purpose is the widely available pin type meter (also known as an
electrical resistance/conductance and destructive meter).
These instruments work by reading across the two pins and detecting the
change in resistance when they come into contact with the timber.Pin
meters will give a pretty good indication of the moisture content of
timber. They are made and calibrated to do this on particular species
of timber for example, Douglas Fir. These instruments work because the
conductivity of timber (also known as the density), is reasonably
constant throughout different timber types and is proportional to the
moisture content. As there are timbers which have different densities
to that which the instrument has been calibrated to, most meters are
supplied with a set of tables which give the adjustments which need to
be made dependant upon the type of timber being tested.
Limitations Of Pin Meters For Building Surveys
described above, the common pin meter has been designed for use on
timber and not any other materials. This fact is often not appreciated
by many users who rely on pin meters to ‘measure’ moisture content in
other materials such as masonry, plaster or wallpaper. This is not
actually possible as there are major variations in, for example masonry
and therefore no consistency between any two samples from different
sites. The same holds for most common building materials.
a pin type meter can indicate, at best, is whether moisture may be
present but they can not measure the actual level of moisture in the
material. The danger of using a pin meter is that the instrument only
reads across the very small area between the pins. This is not such a
problem with timber due to the homogenous nature of it. However, when
looking for moisture in an internal wall, it would be necessary to make
many pin holes all over the wall in order to get a thorough indication
of whether there is a presence of moisture. This is time consuming and
leaves behind unsightly holes. When faced with tiled areas (such as
kitchens & bathrooms) the pin meter can not be pushed through tiles
and as a result no readings can be taken or at best only a surface
reading is obtained. The presence of certain substances on the surface
of the material being tested, such as condensation and salts, will also
affect the readings.