Hardwood Floors December 2024/January 2025

AT THE SITE Pin Moisture Meters for Wood Floors (Continued)

The advantage of pin meters is that they measure small areas and thus can pin-point a moisture gradient or differentiate between surface and core moisture. The other option is using a pinless meter, which measures a larger area, but always indicates only one moisture value depending on which depth the meter is testing at, even if the moisture underneath the measuring plate varies. The advantage is that it leaves no pin holes. To obtain accurate moisture measurements all pin moisture meters – and indeed all moisture meters – have to be corrected for the wood species. The correction settings for different wood species have to be determined through an oven test; they are not based on the specific gravity (which applies to pinless meters only). A correction is necessary because different wood species vary in chemical composition, density, heartwood and sapwood, and structural differences due to growth rings. If you would measure samples of different wood species, all acclimated to 9 percent with a moisture meter that is not corrected for wood species, you might obtain values between 7 percent and 11.5 percent without accounting for the standard deviation. For accurate measurements, the meter has to be set for the correct wood species. Each meter manufacturer provides corrections for their moisture meters. The correction settings often are preprogrammed in the meters. There is one more factor influencing the moisture value indicated by a pin meter: the wood temperature (not the

Meter with pins and slide hammer attachment (D2-M) used to check a problem gymnasium floor.

The ideal floor package D2-M with slide hammer electrode with insulated pins.

air temperature surrounding the wood). If the wood is hotter or colder, the meter should be set for the wood temperature or a correction table should be used. When talking about obtaining accurate moisture measurements by using species and temperature corrections, it should be mentioned that slightly different moisture values will be indicated by the meter, even if all floor planks are of the same wood species and at the same moisture content. This natural deviation accounts for variations mostly within the range of +/-1 percent, but could be as much as +/-2 percent. This distribution appears as a “bell curve” when graphed. It is caused by differences in the wood itself, as mentioned previously, and has nothing to do with the reliability or accuracy of the meter. It is one of the reasons why the NWFA recommends to take multiple moisture measurements per site. It is crucial to record moisture measurements to show a job has been done well. These records also can be referred to in the future in case problems arise. The records should include the meter’s name, the date, the area where the measurements were taken, the wood species correction setting, the temperature setting, the measuring depth, and, of course, the indicated moisture value. A photo is always helpful. Moisture content is an important issue, because throughout its lifespan, wood will stay a hygroscopic material. Its moisture content can change. The only way to measure moisture accurately is by using a moisture meter.

Grete Heimerdinger is the co-owner and vice president of Lignomat in Portland, Oregon. She can be reached at sales@lignomat.com or 800.227.2105.

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