If you work with wood, you must understand how moisture present in the environment affects it. Whether you are making cabinets, installing hardwood floors, carving wood, or doing carpentry, wood moisture content must always be on the top of your mind.
Since wood is hygroscopic, it loses or gains moisture depending on the relative humidity of the surrounding air. Varying humidity levels can cause wood to lose or gain water and shrink or expand.
With the increase in humidity levels, the moisture content always increases. This causes wood to expand. When the humidity decreases, the moisture content also decreases, and this causes wood to shrink. The point where the wood doesn’t lose or gain moisture is referred to as equilibrium moisture content.
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Wood Moisture Content
Before you can use the wood for woodworking, you must ensure that the wood is dried to a moisture content that is within 2 percentage points of the equilibrium moisture content where you are going to use the wood. What does this mean? We’ll explain.
Let’s say that the humidity of the location where you are going to use the wood is 19 to 25 percent. In this case, the equilibrium moisture content would be 6 percent, and the wood moisture content will also be 6 percent.
This means that the wood that is intended for use in that location should be dried to around 6 percent, and it should be kept at this moisture level during the woodworking project. If you fail to do this, you will experience cracking, warping, and other issues after you have finished the wood product.
How Moisture can be Removed from Wood
In order to reach the ideal wood moisture content, you might have to remove some moisture from the wood. Internal moisture in the wood evaporates by itself, but this takes a lot of time. To speed things up, you can use kiln drying. Unfinished wood available in the market is usually kiln-dried to lower its moisture content levels so that it doesn’t suffer from cracking and warping.
It is worth noting that the moisture content of the wood is never constant; it’s always varying. Whether the wood is kiln-dried or freshly cut, it will always interact with moisture in the air. Therefore, just because you have kiln dried the wood doesn’t mean that it won’t absorb moisture. It will still absorb moisture until it establishes a balance with the environmental air.
Acceptable Moisture Levels
There are two factors that impact the wood’s acceptable moisture content – the final use of the wood and the average relative humidity of the location where you will use the wood. Due to these two factors, it is difficult to say how much moisture content is acceptable for wood.
How to Measure Moisture Level in Wood
You can measure the moisture level in wood through moisture meter testing and oven-dry testing. Moisture meter testing is the easiest method, and we have explained it below:
Moisture Meter Testing
This is the most efficient way to test the wood’s moisture content. Wood moisture meters are divided into two types – pin-type moisture meter and a pin-less moisture meter.
Pin-type moisture meters employ penetrating electrodes to measure the wood’s content via electrical resistance. Water conducts electricity while wood doesn’t, so the wood’s dryness can be determined by the resistance to the current.
Dry wood will produce more resistance than wet wood. In order to use pin-type moisture meters, you will have to insert the pins of the meter into the wood surface that you wish to test. Make sure that they are aligned with the grain. Turn the meter on and measure the resistance that you encounter.
Pin-less moisture meters aren’t penetrating and read the wood moisture content by scanning the wood using an electromagnetic sensor. Since pin-less meters can scan the surface of the wood and cover more surface than their pin-type alternatives, they provide a better picture of the moisture present in the wood.
Another great thing about pin-less meters is that they don’t leave any damage pinholes on the surface of the wood. This makes them perfect for measuring the moisture levels of expensive wood materials. Pin-less meters are easy to use. Just put the scanning plate against the surface of the wood and turn on the meter to get a reading.
The Right Moisture Content of Wood for a Woodworker
Since wood warps and shrinks as it dries, woodworkers want it to shrink before they use it. If the wood shrinks after they use it, it will cause problems. You can minimize the expansion and shrinkage of wood after use by drying it to have a moisture content of around 8 percent. To ensure that the wood is dried properly, use a moisture meter before you work with it.
The wood that is freshly cut can have a moisture content between 40 to 200 percent, while the normal moisture content varies from 7 percent to 19 percent depending on the relative humidity in the air.
For woodworkers who construct fine furniture, cabinets, musical instruments, toys, dishes, decorative art, and other wood products, the ideal moisture content ranges between 5 percent and 9 percent. However, this range may vary depending on the geographic region due to varying relative humidity levels.
The Right Moisture Content of Wood for a Flooring Installer
Flooring installers are required to follow the installation guidelines established by the National Wood Flooring Association (NWFA). According to the NWFA, when determining the moisture levels that would be acceptable for wood flooring, a baseline for acclimation must be established by the flooring professional.
Acclimation refers to the process of conditioning the wood flooring’s moisture content to the environment where it is to be installed. For establishing a baseline for acclimation, the installer will have to calculate the right moisture level for the wood by dividing the region’s high season equilibrium moisture content and low season equilibrium moisture content.
For instance, if the expected equilibrium moisture content ranges from a low of 7 percent to a high of 9 percent, the baseline wood moisture content would be 8 percent. The installer should check the moisture content across multiple boards and consider the average of the results.
How to Air-Dry Wood
Stack with Spacers
The wood that comes off the sawmill is extremely wet and may have a moisture content of around 30 percent. When you drive a nail into this wood, water would appear. If you want to air-dry this wood, you should stack it with spacers between every single layer. Make sure to place the wood in a location where there is some breeze to ensure that mold doesn’t grow.
A shady spot outside is good. A garage might not have enough airflow. This is the first phase of the drying process, and it would bring wood moisture levels down to 12 to 15 percent.
Stack Wood in Such a Way that All Sides are Exposed
Winter is a good time to dry wood as heated homes become the ideal drying spaces. The drying process won’t take long if you apply the tricks we tell you. Start by allowing a few days of drying time after each planning and cutting step as you build wood projects. Freshly exposed wood needs the most drying, and you must dry it before you start the project.
To speed up the drying process, stack wood surfaces with all sides exposed. To further speed up the process, point a household fan towards your wood. The added air circulation will make the wood drying faster.
For a woodworker, the ideal wood moisture levels are 6 percent to 8 percent. These levels may vary depending on the relative humidity of the location where you are using the wood.
Before you use the wood on a project, you must ensure that it is at the right moisture levels. If you don’t do this, the wood might expand, shrink, crack or warp, causing problems in your woodworking project.
This is why it is very important that you dry the wood to an adequate level before using it. We have shown you how you could dry the wood before use. Once you have dried the wood, use a moisture level meter to check the wood’s moisture content.
Keep drying the wood until you reach the ideal wood moisture content and then use the wood on your project.
We hope everything discussed above is clear. In case you have any questions or if something is unclear, feel free to reach out to us.
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