WHAT IS A MOISTURE METER AND HOW DOES IT WORK?

About moisture

RELATIVE HUMIDITY (RH)
The air’s ability to absorb water varies with the temperature. The higher the temperature, the more water the air can absorb. The volume of moisture in the air, the relative humidity, is expressed by the unit % RH

DEW POINT
The dew point is expressed in °C and states the temperature at which the relative humidity reaches 100 % RH and water vapour forms (condensation).

MOISTURE IN MATERIALS
The moisture quotient (% MQ) is the difference in percent age between the weight of water in damp material and the weight of the dried material. The moisture quotient can be determined through weighing-drying-weighing. In wood, the moisture quotient can also be measured using electronic moisture quotient meters, since the electrical properties vary with the moisture quotient. In concrete, the moisture quotient can be measured by drilling a hole, vacuum it clean, seal it and leave it to stand several days until it reaches equilibrium (see moisture balance). Then you can measure the

relative humidity in the drill hole, which in turn can provide the moisture quotient in the concrete, because you know the absorption curve for the specific type of concrete. It is important that you vacuum carefully, properly seal around the moisture sensor and leave it to stand in the drill hole until it reaches equilibrium. The drill hole should rest for approx. 48 hours before measuring so that the correct moisture quotient equilibrium can be achieved. Wait for at least half an hour after inserting the sensor into the hole before read-ing the measured value

MOISTURE METER SELECTION

Ask yourself the following questions before selecting a moisture meter:
What materials will I be measuring on?
How far into the material must I measure?
What construction will I be measuring on?
With what degree of accuracy and on what moisture level will I have to measure?
Follow the manufacturer’s recommendations regarding maximum moisture quotient/moisture content before treating the surface.

PIN METERS
A so-called pin meter measures the moisture indirectly by measuring the resistance (conductance) with an electrical current that goes from one pin to the other. A pin meter measures the moisture as far as the pins are inserted. Select longer measuring pins to measure moisture further into the wood. To measure so-called moisture gradients, you will require Teflon-insulated measuring pins

ADVANTAGES OF PIN METERS:

Proven method that has been used for a long time in the wood and construction industry
Fast. The measured results are displayed immediately on the display.
Possible to detect moisture gradients.
Good on uneven material surfaces

DISADVANTAGES OF PIN METERS

Destructive measuring method. Pins must penetrate into the material to be able to measure.
With high moisture quotients in wood, the water may be ionized together with resin. This means that the moisture quotient will appear to vary.
Temperature-dependent, requires temperature compensation for best possible accuracy.
The measured result may be affected by impregnation agents.

THINGS TO CONSIDER:

A strike hammer makes life easier when measuring with Teflon-insulated measuring pins.
Insert the pins perpendicular to the tree rings.
Do not measure in end sections, the cell structure in the wood means that the moisture quotient in the ends can vary dramatically compared with the moisture quotient further into the wood.
With repeated measuring, e.g. when checking moisture damage, insert the pins into new holes. Old holes oxidize and display a lower measured value.

CAPACITIVE/NON-DESTRUCTIVE MOISTURE METERS
A capacitive/non-destructive moisture meter measures changes in the material’s capacitance which vary with the moisture content. The instrument emits a high frequency signal. The frequency of the electrical signal will vary due to the capacitance of the material.

ADVANTAGES OF CAPACITIVE MOISTURE METERS:

Non-destructive measuring method, does not affect the measured object.
Fast. Immediate results, measure in as many places as necessary.
Independent of temperature, requires no temperature compensation.

Density-dependent, requires material adjustment for best possible accuracy.
Detects rebar and other metals that increase the moisture quotient if these are within the measuring depth and recording range.
Requires that the sensors are positioned against the material.