What Is Kiln Dried Wood?
Wood is one of the most versatile materials. Aside from being used as building material, it can also be used for heating and lighting. Although you can use wood as it is, most builders and contractors prefer to dry their wood before use. The most common way to dry wood is placing it under the sun. Another way is to use an oven or a kiln to dry wood faster, creating kiln-dried wood.
Characteristics of kiln-dried wood
After harvesting wood, lumber is still “green” which means that wood is still filled with moisture. Green lumber is very moist. Use it to make any furniture and you will see that it can warp and shrink for every percent of moisture content (MC) below the fiber saturation point.
Lumber companies dry their wood using a kiln. They dry their wood in a controlled environment using carefully monitored humidity and temperature levels to prevent over-drying or under-drying wood. A kiln dries wood to the correct MC for its intended use letting wood maintain its natural stability and dimension. Although wood should be dried, it should not be over dried. This can warp or shrink wood and will not have the correct MC for its use.
Kiln drying is non-permanent
Unfortunately, kiln drying is permanent. Wood is known as hygroscopic, this means it can absorb or release moisture. The moisture may have left the inner parts of the wood but it can still be affected by a direct water source such as rain, moisture or humidity in the air. This nature of wood to absorb or release moisture may apply to any kind of wood even if it has been kiln-dried. Once the kiln-dried wood leaves the factory, its MC can change at any time. It can change during transportation, manufacturing, or even when it is placed in a woodworker’s garage.
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Drying your own wood with a kiln
Although it is very easy to just order kiln-dried wood, this might be very expensive. This is why some homeowners dry their own wood. One option is air dry green wood. However, air drying can take several months and will not achieve a low enough MC without the help of kiln drying.
One of an efficient, cheap and safe way to dry green wood is by using solar kilns. You can build your own Building a backyard solar kiln because it is inexpensive and is very easy to operate. Solar kilns won’t dry wood that fast so you don’t need to worry about overdrying your wood. It is only during the final stages of drying when you need to measure MC to determine if the wood is done.
Checking wood’s internal moisture
When learning to dry lumber, especially lumber that is thicker than one inch, woodworkers should monitor the moisture content of wood on a regular basis to avoid rapid drying. The best way to do this is by using a moisture meter.
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With a moisture meter, woodworkers can monitor the drying rate of sample boards and compare the daily rate of moisture loss for the particular species. There is a safe rate for each species and this is referred to as the loss of moisture in one day.
Safe rates for drying 1 to 2-inch thick lumber of a variety of wood species are available in safe rate tables online. These safe rates must be followed until MC drops to 20%. Do not exceed the safe because this can cause warping and other defects in the lumber.
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Using moisture meters
Woodworkers can use a pin meter or a pinless meter. Pin meters have varying lengths of pins or probes which tests wood at different depths. The major disadvantage of this type is that only a relatively small area is tested with each insertion. This type can also be sensitive to wood temperature while pins can easily damage when inserted especially on hard wood.
Broken pins can give inaccurate readings.
Pinless meters don’t penetrate the wood’s surface, so they won’t damage the wood. Another advantage is that a woodworker can scan board feet of wood quickly and easily. Pinless meters take a composite average of the MC from the surface up to 1 inch deep. The MC readings are obtained from a greater surface area than pin meters.
Kiln-dried wood is standard in making furniture and for wood used as building material. This type of wood will not warp and can be used for most projects. Kiln-drying is not permanent because of the hygroscopic. Wood can release and absorb moisture despite being dried completely.