Hardwood Floors December 2018/January 2019

By Grete Heimerdinger

3. Differences between different wood temperatures. Measuring moisture of hot or cold lumber requires further corrections. The electrical resistance changes with the wood temperature. Moisture meters are calibrated for a wood temperature of 70˚ F. If the wood is between 55-85˚ F, the difference in readings is small. Above 85˚ F or below 55˚ F, the measured value should be corrected for the actual wood temperature. Some pin meters have built-in temperature corrections while others come with a correction table. Caution: It is hard to establish the correct wood temperature at the measuring depth where the tip of the pin has been driven to. If the ambient temperature has been stable for the last few hours, you can take the ambient temperature. If the ambient temperature has changed, then use the average during the last few hours.

three-dimensional field underneath the measuring plate(s). (See photo, the entire area between surface and core is included in the measuring field.) If there is more water in the test sample, the indicated moisture content is higher. Less water gives a lower moisture content until the meter cannot measure anymore. If moisture varies within the three- dimensional measuring field, the average moisture is indicated. If different materials, for example, wood and concrete, are within the three-dimensional measuring field, the indicated value is not a true moisture percentage. If there is not enough material underneath the measuring plates, the indicated moisture value is not accurate either. It could be because the test sample is too narrow to cover the entire measuring field, or maybe because the test sample is not thick enough and there is not enough material underneath the measuring plates to give an accurate reading. In other words, wood planks that are only 1/2" thick cannot be accurately measured when the meter is reading 3/4" deep. The subfloor will influence the results. Some meter manufacturers offer dual-depth meters to accommodate for these variations in material thickness.

piece of wood, even within the same wood species, is different in color, structure, and electrical characteristics. Moisture readings from sample boards of the same species at the same moisture content show small deviations. Below fiber saturation point at about 25 percent, these deviations are small and in general stay within 1-2 percent.

The only tool to allow measuring the subfloor without removing the floor planks on this basketball court is to use a Slide Hammer Electrode with Teflon coated pins. 2. Differences between different wood species. More significant variations are found between different wood species. To stay within the variations of 1-2 percent, moisture readings have to be corrected for the wood species you are measuring at the moment. Calibration corrections are done internally by the moisture meters. The user selects either a wood group (species with similar correction algorithms are in the same wood group) or the individual wood species. Wood group codes and species settings are specified by the manufacturer. Note, the correction algorithms for pin meters are not based on specific gravity; they have to be found by oven tests and mathematical calculations.

Pinless meters leave no pin holes and allow checking a lot of floor planks in a short time. Pin and pinless meters are often used side by side in the flooring industry. As shown in the photo, readings should be taken, while the meter is slightly pressed against the floor plank by hand. Do not kick the meter along the floor and read the display. MEASURING WITH YOUR PINLESS MOISTURE METER: Most pinless meters use electromagnetic wave technology. The indicated moisture content includes all materials in a

When the floor plank is thick enough to fill the entire measuring field, true moisture percentages are displayed if the meter is set to measure that particular wood species.

the magazine of the national wood flooring association

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