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.
- 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
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.