Can the moisture content in a wood floor be really 4%? How can wood achieve such a low moisture content? If someone in Portland Ore., for example, claims that a wood floor measures 4%, I would be very skeptical. However, there are places where the moisture could be very low.
Since extreme relative humidity conditions are not typically experienced in the Portland, Ore., metro area, I would argue that any report of 4% moisture content in a wood floor is likely inaccurate. The meter may be defective or it might have been set to the wrong setting for wood species corrections.
Wood is a hygroscopic material, meaning it absorbs and loses moisture if exposed to higher or lower relative humidity for a long period of time. For each relative humidity and temperature level, wood is stable at a certain moisture content:
- At 20% relative humidity and 700F wood is stable at 4.5%
- At 45% relative humidity and 700F wood is stable at 8.5%
- At 65% relative humidity and 700F wood is stable at 12%
There is two ways to understand this. Let’s use the first example: If wood has a moisture content of 4.5%, the relative humidity must remain at 20% for the wood to stay at that level. Conversely, if wood has a moisture content of 8.5%, it will eventually decrease to 4.5%, if the relative humidity is maintained at 20% for an extended period of time.
Dry conditions, such as 20% relative humidity can occur in some homes in the cold winter months in the northern U.S. Wet conditions like 65% relative humidity can occur in wet, warm coastal areas during the humid summer months.
The best way to avoid these extreme conditions is an HVAC system capable of keeping the relative humidity within the ranges recommended by the NWFA: 30%-50% relative humidity at temperatures between 600F and 800F.
The right tools
In order to get correct measurements of moisture content in solid or engineered wood floors, any meter (pin or pinless) has to be adjusted for the specific wood species. When measuring engineered floors, the setting should be recommended by the floor manufacturer.
When selling, installing or inspecting floors a good moisture meter is a must. More importantly, the key is knowing how to use it properly and to be able to report the measurements correctly and to understand the findings. Do not report a moisture content of 4% without questioning its validity and investigate further as to why the meter shows such a low value.
Whenever possible, when reporting a measurement, it’s a good idea to include a photo that shows the measured value, the settings for moisture content and depth, as well as the name of the meter and the location, where the measurements were taken, etc. (The above photo shows all important information for a valid measurement: a wood moisture of 7.3% taken with the Ligno-DuoTec BW with a species setting of 66 and a measuring depth of ¼ inch, located near the molding.)
Grete Heimerdinger, vice president at Lignomat, has been heading the moisture meter division of the company since 1981, when the first pocket-size mini-Lignos were introduced. She graduated from the Technical University in Stuttgart, Germany, with a teaching degree in Mathematics and Physics. For more information, contact Lignomat at 800.227.2105 or email sales@lignomat.com.
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