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A Definitive Guide to the Wood Moisture Meter
Wood is an attractive raw material, and since it’s durable, available in different colors and textures, it’s widely used in manufacturing. But as any woodworker will tell you, a moisture meter is necessary because wood shrinks and expands according to the seasons, and to maintain quality, a moisture device has to be used to prevent cracks and splits.
What Types of Moisture Meters are Available?
The wood moisture meter is available in two general types, and both are used in woodworking and lumber applications.
Pin Type Meters
The pin type has two pins that pierce into the wood at a depth you specify (and also depending on the meter you purchased). These meters are valued by woodworkers because they can indicate the moisture level inside the wood or board.
By relying on insulated pins, the uncoated tips are the only elements open to the wood fiber, and this results in more precise readings of moisture level even at varying levels of penetration. As it is, the pin meter is still the most accurate method to measure moisture gradient, which is the difference between core and shell moisture content.
There are various types of log moisture meter pins, but what they all share in common is being able to give accurate readings and serving as an indicator if the wood is evenly or unevenly dried out. Furthermore, the area between the pins indicates the highest moisture level so it’s easy to detect.
As has been pointed out earlier, these pin meters can tell the difference between the surface and core moisture via the insulated pins. In addition, these pins are not affected by the shape or surface texture provided both pins can be inserted.
Pinless Type Meters
Pinless moisture devices measure the moisture nearest the magnetic field surface. Because of its design, the pinless type is ideal for scanning a finished product quickly and locating a problem area. However, this device cannot distinguish between core and shell moisture content and is not as effective when it comes to sensing moisture gradient. Furthermore, some of the readings by these devices are influenced by surface moisture.
Despite the limitations, these devices can be valuable if used in the right situation. They are for instance, handy in scanning large areas and serving as an indicator of significant moisture levels across the board as well as water pockets. These meters are also used for finding the average moisture in three dimensional fields.
Their limitations include the inability to tell the difference between core and surface moisture. Furthermore, these meters require a flat measuring area and a smooth surface for the best results.
How Does the Device Work?
Similar to the protimeter, these moisture devices work on the electrical resistance principle. What a pin type meter does is use the board as a circuit element by driving a couple of electrodes or pins into it. This technique is very effective because moisture is a good conductor of electricity, and dry wood is an excellent insulator.
Pinless meters on the other hand, rely on the capacitance method which is based on the relationship between the wood’s dielectric properties and the moisture content. If you’re not familiar with capacitance, it refers to the capability of a body to hold an electrical charge, and dielectric happens to be an electrical insulator. Both the dielectric properties and resistance change in proportion to the level of moisture inside them and in a particular range.
Why Do You Need to Check Wood Moisture?
A wood moisture meter is necessary because if the level is not monitored, it will have an adverse effect on the finished product. With such a device you’ll be able to determine the acceptable moisture content. Currently the acceptable dryness level for wood for fine furniture is 6% to 8%, and there is little variation amongst the pieces and of the core and shell.
The suitable moisture content also depends on the climate. To find out the equilibrium moisture content (EMC) in your area, simply hang thin, small wood species samples and measure their readings daily. If the moisture level is consistent it means they have attained the equilibrium level. This is going to change with the seasons of course, but you’ll have a good starting point.
The EMC by the way, is the point when the wood is neither losing or gaining moisture. However this is dynamic and will change relative to the temperature and the humidity. To simplify things further, a moisture metering device is used to gauge the percentage of water in the wood.
By using a metering device, it becomes easier to assess if the material is ready to be used, in need of more work or has suddenly gone dry or wet. Just like paper, wood is sensitive to moisture and its physical properties are affected by it. Logs that have been newly cut for instance may have a moisture content (MC) of up to 80%, and with some species it is even higher.
In many parts of the US, the minimum moisture content from air drying is 15% so other methods have to be used to remove the moisture. This is where the meters come into play because they track the level of water inside the wood so the woodworker knows if it’s acceptable for the intended goal.
Because knowing the moisture content is so important, meters are considered essential tools for woodworkers, carpenters, hobbyists and anyone who does serious woodwork. Those who install wood floors for example, need to know the wood MC as it has to correspond with the humidity in the area. If this step is ignored, it could lead to all sorts of problems like cracking, sunken joints and more.
Moisture meters are widely available so finding one won’t be a problem. However, the quality varies among these products so some research is required. But it is to your advantage that you now have a greater understanding of how these devices work so you won’t be swayed into making a decision based on mere claims alone.