- Ensure your meter is calibrated.
- Account for the wood species being measured.
- Set the correct depth setting if the meter has adjustable depth capabilities.
- Take multiple readings across the surface to get a complete assessment of the wood’s moisture content.
- Have at least a one-inch air gap underneath the wood being measured.
- Only take measurements where the entire sensor plate can lay flat on the wood surface.
- Press down on the moisture meter with the right amount of pressure.
- Don’t take a reading where there is noticeable defect or knot.
- Make sure there is no visible moisture or water on the wood surface.
- Take good care of your meter.
- Don’t ignore the manufacturer’s documentation.
- Select a sample of wood that is approximately 12% moisture content, with all edges being true.
- Carefully measure the Length, Width and Thickness dimensions of the sample, preferably using a caliper. Convert the Length, Width and Thickness measurements to feet (ft.).
- Carefully measure the weight of the sample, to the tenth of an ounce. Convert the weight to pounds (lbs.).
- Using the volume and the weight of the sample, and the weight of a cubic foot of water, calculate the specific gravity.
If two meters are not of the same manufacturers, readings will likely not correspond, because of the different calibrations used. Often, there are different species and temperature correction factors.
Even readings on two meters of the same manufacturer may vary. Assuming both meters are electrically correct, the difference usually can be attributed to use of different electrodes, pin penetration, and species and temperature corrections. When meters are used for lumber inspections by vendors and buyers, the two parties should have a basis for comparing readings obtained with the instruments they are using.
A little care goes a long way toward trouble-free service:
- Store the meter in clean, dry place
- Change the batteries and pins as needed
- Keep the meter and electrode clean by using biodegradable cleanser sparingly on external parts only
In most cases, no. To verify this, use insulated pin to make individual tests by touching the outer ply, glue lines and center plys. If the glue reads the same as wood, use the meter on plywood as you would any solid material and take the readings at face value, without species correction.
After moisture content and a moisture gradient, if one exists, wood temperature is the most important factor affecting the accuracy of your readings. As wood temperature increases its electrical resistance decreases and indicated moisture content rises. The lower the temperature, the lower the indicated moisture content. Depending on the temperature and moisture content, you may have to make a correction.
With a pin-type meter, these conditions are not a problem. Just drive the pins as you would normally, ensuring firm, positive contact and detect unknown gradients.
Pinless meters, however, need firm contact to a flat surface so the readings on uneven surfaces may be unreliable.
Board width is not a limiting factor when using a pin type moisture meter. As long as the pins make good contact, the meter can be used on anything from small dowels to wide planks.
For accurate results with a pinless meter, the material you’re testing must be at least the width of the scanning area on the bottom of the meter. Otherwise, the meter will not make firm contact with the board and may provide inconsistent, unreliable readings.
In cold and/or dry climates, static charges may cause erratic meter readings in the range below 8%. Measuring such high resistance under there conditions is difficult enough. The analog meter pointer “jumps” all over the scale or the digital display may flash erratic numbers. To minimize the effect of static:
- Try not to let the electrode cable dangle.
- Drive the electrode pins into the wood with the meter turned off, and then turn the meter on when you are ready to take the reading.
- After driving the pins, place your hands next to them on each side of the electrode to help discharge the static from the board.
- You can also try passing a damp cloth over the board’s surface to pick up any static charges before driving the pins.
These suggestions are not guaranteed. However, depending on the conditions, any one of them can work, either alone or in combination with another.
There are two types of moisture meters typically used in the flooring industry. Pin-type meters, which utilize the principle of electrical resistance, use wood or other hygroscopic materials as an element in a circuit by driving two pins or electrodes into it.
Pinless meters use radio frequency signals to penetrate the material being tested. There is
no pin intrusion into the surface of the material you are checking.