How To Use
Moisture Meters
The increase of
water intrusion and other moisture
related problems in construction have
made the use of moisture meters more
popular than ever. However, one must
understand that a moisture meter is
merely a tool and provides one piece of
information to assist the user in
reaching an assessment. It is also
critical for the user to be aware of how
moisture meters work.
There are two basic types of moisture
meters: surface (scan type) meters and
probe meters.
Industry professionals generally agree
that scan-type, or non-intrusive, meters
are not terribly reliable and can give
readings that may mislead the user or
give a false sense of security. They are
popular with home inspectors because
there is no need to probe or penetrate
the cladding material to get a reading.
This method is also appealing to building
owners, who do not want holes put into
their walls.
The probe-type meter is much more
reliable. As the name implies, the probes
must touch the material that is to be
tested for a reading. These meters work
on the basic principle of electrical
conductivity. In other words, the more
moisture in the wood, plaster, cement or
gypsum, the more conductive it is.
Probe type meters can also give
misleading information. For example, if a
probe-type meter were to touch a metallic
object, the reading would be 99.9
percent, which could lead an investigator
to assume the wall is completely soaked.
With cement plaster, it is not uncommon
to accidentally touch the metal lath and
get a 99.9-percent reading while the wall
is dry.
Most probe-type meters come with a
separate attachment of long probes to get
behind thicker cladding materials. An
important factor often overlooked with
the long probes is the insulating coating
on the probes. This insulation protects
the probes from getting false readings
from materials that could touch the sides
of the probes.
What is Dry?
Wood is considered “dry” at
19 percent or less moisture content per
the Canadian Wood Council. Wood that has
a 28-percent moisture content will have
wood fibers that are completely
saturated. When the moisture content of
wood is above 28 percent for prolonged
periods of time, decay will begin. Indoor
wood will stabilize at 8 to 14 percent,
while outdoor wood stabilizes at 12 to 18
percent.
On a recent investigation into an EIFS
project, readings were 99.9 percent, and
some assumed the walls were saturated.
Further investigation discovered that a
drainage mat that incorporated a foil
type backing had been used on the
building. This produced intermittent
readings of 14 to 16 percent (normal) and
then suddenly a 99.9-percent reading when
the probes touched the metallic foil.
Another concern is the use of the long
probes. The length of the probes provides
the opportunity for the sides of the
probes to touch objects and give false
readings.
The probes come from the factory with a
thin insulating paint coating with only
the tips exposed. However, the thin
coating will wear off relatively quickly,
and you can get false readings. To
re-insulate the probes, some inspectors
use the same plastic coating used to
protect electrical wires or a thin straw.
Slip on the protective cover that is
slightly larger that the diameter of the
probe and apply some heat. This will
cause the plastic to melt and shrink and
to adhere to the probes to protect
them.
Courtesy of EIFS
Alliance