Everyone who has spent time working with wood knows that the moisture levels can vary from piece to piece and from source to source. They also may have seen their wood change after it was delivered to their shop or job site – twisting, cracking, warping and otherwise not retaining its shape or dimensions. When working with wood to create your own projects, this can be problematic. When working with wood flooring, this can be disastrous.
Why does it happen? Wood is a hygroscopic material that absorbs and releases moisture from its environment, and until it is fully sealed, this is an ongoing, never-stopping process. Sawmills and wood product manufacturers invest heavily in monitoring wood’s moisture content and removing excess moisture from wood. However, even with their care, once wood is transported to another location, the moisture cycle of wood will continue to work to try to balance with its environment.
How does that present a problem for the people and professionals who work with wood? Any time moisture content is too high (or too low) for its use and environment, the end result is put at risk, along with a few other things along the way.
The Stakes of Unknown Moisture Content
First, let’s look at some of the challenges if wood is too “wet” or has high moisture content.
Wood that has a high moisture content (or MC) level will begin to shrink in all dimensions as it begins to lose that excess moisture. Most impacted, though, is width and thickness. If you have fit wooden floor boards together that have excess moisture, that change in dimension can lead to cupping, gaps, or buckling. Not a pretty sight and, in extreme cases, a safety hazard too.
Trying to put “wet” lumber through a planer, a jointer, a sander or even cutting it with a saw can cause both damage to the tools and danger to you. Wet sawdust or shavings catch on blades and other moving parts and can effectively “gum up” the works inside a machine, or promote rust on metal parts (like knives) and shorten their life spans. High MC wood is also more prone to catching or kick back.
Wood with higher moisture content levels is also at risk of additional damage during the working process. Because the wood fibers are, in effect, softened with the additional moisture, tools are more likely to tear or rip the wood instead of cut it. Tear-out, checking, and gouging are more likely on high MC lumber. Even sanding can tear up the surface, rather than smooth it, when the wood’s MC level is high. It’s also a must to remember that after the wood dries, the chances of cupping, raised grains, burring or dimensional changes mean the wood may only need to be worked again.
Unless you use glue or adhesive specific to wet situations, high wood moisture content can mean glue joins do not hold properly over time. If the wood dries after it has been glued, that inevitable shrinkage will put joins at risk as it tries to pull away from the other woods. For furniture joins or glued-down flooring, where use adds stress to the join, this can be disastrous. Moisture can also slow glue curing times.
What about the reverse situation? What if wood’s MC level is too low?
Just as drying wood shrinks, wood that is absorbing moisture from its environment will swell in size. While that might cause a tight fit, or even a potential split, in some wood projects and in wood floors it can also cause crowning or buckling.
Overly dry wood can be more brittle, meaning nailing, sawing, or other aspects of installing or woodworking can lead to splits, cracks, knot loss and other damage, particularly if working across the grain. Trying to carve or turn overly dry wood can also lead to more splintering on the surface.
Chisels, saw blades, drill bits and other tools can also dull tools faster than wood that is at the correct moisture content for its area and species.
Ultimately, there is a variety of reasons to monitor wood moisture content, as both levels that are too high and too low can be problematic. How can you tell which is which?
Like many situations, the answer is, “It depends”.
When is Wood Wet (Or Dry)?
If a living tree has just been cut, it’s wet. That’s a guarantee. After that, though, any rule of thumb will be no more than an estimate.
While there are many guides or tables available to help identify the correct moisture content for a wood species or a geographic region, ultimately moisture content is best monitored with an accurate wood moisture meter. Even within one geographic region, temperatures and ambient humidity can vary. In interior installations, the operation of the HVAC system will play into wood’s moisture content levels.
Wagner Meters’ wood moisture meters give you fast, accurate and easy-to-operate assessments of wood moisture content. Their non-damaging pinless technology even lets you “scan” many board feet of lumber to help identify potential wet spots or changes within wood stock or wood flooring. Once wood or wood flooring is delivered to its job site, a pinless meter lets you easily monitor the changing MC of the wood.
The target, really, is to identify the point when the wood has reached a balance with its environment, a state referred to as equilibrium moisture content, or EMC.
The True Target: EMC
Think of EMC as moisture content in context. The natural give and take of wood with the moisture of ambient humidity will eventually come to a resting state, and that will be the best time to move ahead with the woodworking or the wood flooring installation. And knowing that your wood has reached its EMC will give you the confidence to move ahead with less risk of a project damaged by a moisture content level that is too high or too low for conditions.