For those who work with wood, the moisture content of wood must always be in our minds. Because the wood moisture level is affected the wood products’ quality, such as the expansion, shrink, crack, warp and mildew, and other quality problems. So before we use the wood, you must ensure it is at the correct moisture level.
What is the moisture content of wood?
Wood Moisture Content is the weight of water in a piece of wood. The moisture content can be calculated using the weight of the fully dried wood as the basis. Calculation formula: W = (Gs – Go) / Go × 100% where: W – absolute moisture content of wood; Gs – wet wood weight; Ggoo – absolute dry wood weight. Wood in buildings usually has 5% to 15% wood moisture content.
What is the acceptable moisture content of wood for our wooden crafts?
Customers require wood products with a moisture content of 14% or less. Considering different measuring instruments, our factory’s requirement for humidity is around 12%.
How do we control the moisture of the wood?
The paulownia and Chinese fir wood we purchase is delivered directly from the sawmill to the mill. The wood is very wet, with about 40% or more moisture. Usually, we air-dry this wood; there is space between each layer of wood. It takes about three months, and the moisture reaches less than 12% before storage. Pine and Cypress are well-dried wood, and moisture is below 16%.
Wood is hygroscopic. As the surrounding air’s relative humidity (RH) changes, it will absorb and release water until it reaches equilibrium with the surrounding air. The factory strictly monitors moisture and temperature in the warehouse where the wood is stored.
1. Recorded twice a day, at 9:00 am; 2:00 pm.
2. Open the windows for ventilation and air dispersion on sunny days.
3. When the humidity reaches 65% or more, place lime powder to dehumidify in the prescribed area, turn on the fan and turn on the air conditioner for ventilation in the workshop with the air conditioner.
4. Note: In summer, when the air’s moisture is very high, and the wood is more challenging to dry naturally, the wood is put into a drying room for drying.
How do measure the moisture content?
There are two main types of wood moisture meters: pin and needleless.
The needle meter uses a penetrating electrode and electrical resistance to measure the moisture content of the wood. Water conducts electricity, and wood does not. Dry wood creates more resistance than wet wood.
Needle Moisture Meters
The general procedure for using a pin moisture meter is as follows.
Insert the pins into the surface of the wood to be tested.
Make sure they are aligned with the grain, not through it.
Turn on the meter. The current will then move from pin to pin and measure the resistance encountered.
Needleless Wood Moisture Meter _Inductive wood moisture meter
Inductive wood moisture meters are non-penetrating and read moisture content by scanning the wood with a non-damaging electromagnetic sensor. Because Inductive wood moisture meters skim the wood surface and cover a larger area than pin meters. They provide a more comprehensive picture of wood moisture content.
The inductive wood moisture meter does not leave damaging pinholes on the wood surface. This makes an Inductive wood moisture meter ideal for measuring the moisture content of items such as expensive hardwood flooring.
The Inductive wood moisture meter is even easier to use. Press the scanning plate onto the wood surface, turn the meter on, and receive a reading.
The equipment we used – was the inductive wood moisture meter AD-100.
An inductive wood moisture meter selects the density depending on the object to be measured.
1 gear: ≤ 0.45 2 gear: 0.45<p≤0.55 3 gear: 0.55<p≤0.65 4 gear: 0.65<p≤0.75 5 gear: 0.75<p≤0.85 6 gear: 0.85<p≤0.9 7 gear: 0.9<p≤0.95 8 gear: 0.95<p≤1.0 9 gear: 1.0<p≤1.15 10 gear: 1.15<p≤ 1.31
1: Due to the different wood structures, its dielectric coefficient is also different. The above gears are recommended gears. If there is an error, please make a comparison calibration. For example, if you measure a wood with available moisture of 8% and turn the dial to 10, the number will be 08.0. It would be best to turn the dial to 10 when measuring the same wood in the future.
2: Hold the meter in your hand (the probe should not be in contact with the measured object), turn on the switch (press the yellow button), and display the figure within 00.5. If it is not within its range, you should slowly adjust the zero knob (ZERO) so that the digital display can be within 00.5.
3: Measurement: Since the instrument uses electromagnetic wave scanning technology, its scanning depth is 50 mm, so when measuring, the wood thickness should be at least 50 mm or more. The probe will be pressed against the wood sensor round head and wood contact for a straight line. The instrument and wood to maintain parallel: open the switch and be digitally stable; the displayed number is the moisture value of the measured object.
Note: Because the high frequency has intense penetration, therefore, in the measurement, the bottom and around the measured object can not have an iron plate or magnets.
We commonly used wood: paulownia wood: choose between 1-2; pine, juniper, and Chinese fir wood are generally selected: between 2-3; using the electric wave-type measurement thickness is required more than 5cm, if the thickness does not reach 5cm, we carry out the suspended measurement, without touching other objects.
I hope that through my article, I can give you a better understanding of moisture and our factory.
