Moisture meters are essential in avoiding wood moisture problems such as shrinking, warping and cupping. Both pin and pinless meters are available. It is not an easy choice between the two meter types, because both have advantages and disadvantages.
Pinless meters. Pinless meters use electromagnetic wave technology, which measures the density in a three-dimensional field underneath the measuring pad. The average moisture in the measuring field is indicated. So if the moisture varies within the measuring field, the pinless meter shows the average. For accurate values, the measurements have to be corrected for different wood species. Advanced pinless meters have those corrections built-in and only a number needs to be selected. For all other meters a correction should be used to obtain accurate values. Wood temperatures do not affect measurements; therefore no correction for wood temperature is necessary.
There are several advantages for pinless meters. In a short time a large number of boards can be scanned and the measurements leave no visible marks – no pinholes. Even though pinless meters do not indicate differences between surface and core, the meters can detect water pockets and higher moisture levels across the board. The Ligno-Scanner SD with its unique dual-depth feature (measures 1/4” and 3/4”), for example, can indicate core and surface moisture.
However, pinless meters require a somewhat flat and smooth surface. The measuring area should be at least as big as the measuring pad on the meter. Also, the measuring depth is crucial; moisture values are too low for materials thinner than the measuring depth. Pinless meters cannot read any deeper than the measuring depth indicates.
Pin meters. Pin meters measure the electrical resistance between two pins. The electrical resistance changes with the moisture content of wood. If moisture varies within the small segment of the non-insulated part of the pins, the highest value is indicated. Wood species corrections are necessary to obtain accurate measurements. Most pin meters have built-in corrections for different wood species. If lumber is hot or cold the electrical resistance in the wood changes; therefore wood temperature corrections are necessary for hot or cold lumber.
For thorough quality control, moisture should be measured down to the core. The slide-hammer electrode with Teflon-coated pins is the ideal tool. As the pins are hammered towards the core, consecutive measurements indicate if the wood is dried to the core. Meters measure down into the board, even if the boards are several inches thick. If only small meters with integral pins are available, core readings can be obtained by cutting the wood and measuring the end grain.
As for general usage, pin meters are more versatile. Every piece of wood wider and longer than the distance between the pins can be measured, including round, small and oddly shaped pieces. Round table legs or oddly shaped products cannot be measured with a pinless meter.
Making the choice. If measurements are taken before or during the manufacturing process it may be easy to hide the pin holes. If the product is already finished and the moisture content needs to be checked, a pinless meter could be the best choice.
Regardless of using pin or pinless meters, it is strongly recommended to check the moisture content when drying lumber, buying or selling wood, making furniture and cabinets or dealing with hardwood floors.
It is absolutely necessary for a floor installer to take moisture measurements at the time the installation is finished, which is a great application for the pinless meter with dual-depth to pinpoint the moisture distribution within the floor planks. In case of complaints down the road, moisture conditions can be reevaluated and compared to the time of installation. This information will allow an inspector to determine the source of the problem.
Grete Heimerdinger was a science teacher in Stuttgart, Germany, before moving to the United States, where she has been vice president of Lignomat USA for more than 30 years. Along with being actively involved in product development, she is a member of the ASTM task groups C11 for measuring moisture in gypsum, and ASTM F-2170 for measuring moisture in concrete. For more information visit Lignomat’s website at www.lignomat.com.