From the artistry of a seasoned carpenter to the precise craftsmanship of a flooring expert, working with wood demands precision and understanding. But a hidden variable can twist your plans out of shape – moisture content (MC) in wood. Too wet, and it warps; too dry, and it becomes brittle.
Navigating the delicate balance of wood’s moisture content isn’t merely a choice but a necessity.
This comprehensive guide will explore the science of wood’s relationship with moisture, the pitfalls of getting it wrong, and the tools you need to get it right.
- Moisture Levels Can Vary
- The Stakes of Unknown Moisture Content
- Trapped Moisture in Wood
- When Is Wood Wet (or Dry)?
- The True Target: EMC
Whether you’re a seasoned professional or a DIY enthusiast, understanding the stakes of unknown moisture content in wood is vital to your success. Read on to ensure your next project stands solid and trustworthy.
Moisture Levels Can Vary: Handle with Care
Everyone who has spent time working with wood knows that moisture levels can vary from piece to piece and from source to source. They also may have seen their wood change after being 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 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 fully sealed, this is an ongoing, never-stopping process. Sawmills and wood product manufacturers invest heavily in monitoring wood’s moisture content (MC) and removing excess moisture from the wood.
However, even with their care, once the wood transports to another location, the moisture timber cycle 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 MC is too high (or too low) for its use and environment, the result is 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 the wood is too “wet” or has a high MC.
Shrinkage
Wood with a high MC level will shrink in all dimensions as it loses excess moisture. Most impacted, though, are width and thickness. If you have fit wooden floorboards together that have excess moisture, that change in dimension can lead to cupping, gaps, or buckling.
These changes are not a pretty sight and, in extreme cases, a safety hazard.
Tool Wear
Trying to put “wet” lumber through a planer, a jointer, a sander or even cutting it with a saw can cause both damages 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 lifespans. High MC wood is also more prone to catching or kickback.
Wood Damage
Wood with higher MC levels is also at risk of additional damage during the working process. Because the wood fibers are, in effect, softened with the extra 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.
Adhesive Problems
High wood MC can mean glued joints do not hold appropriately over time unless you use glue or adhesive specific to wet situations. 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.
This can be disastrous for furniture joins or glued-down flooring, where use adds stress to the join. Moisture can also slow glue curing times.
What about the reverse situation? What if wood’s MC level is too low?
Swelling
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.
Brittleness
Overly dry wood can be more brittle, meaning nailing, sawing, or other installation aspects can lead to splits, cracks, knot loss, and further damage, mainly if working across the grain. Trying to carve or turn overly dry wood can also lead to more splintering on the surface.
Tool Wear
Chisels, saw blades, drill bits, and other tools can dull tools faster than wood at the correct MC for its area and species.
Ultimately, there are various reasons to monitor wood MC, 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.”
Trapped Moisture in Wood
Trapped moisture in wood refers to the moisture trapped within the wood fibers, leading to potential issues and damage. When wood is not properly dried or sealed, it can absorb moisture from its environment, causing it to swell, warp, or even rot.
Trapped moisture can also affect the performance of adhesives and lead to joint failure. To prevent these problems, it is crucial to monitor and control the moisture content of wood, ensuring that it reaches a state of equilibrium moisture content (EMC) with its surroundings.
By using accurate wood moisture meters and taking appropriate measures to remove excess moisture, woodworkers can avoid the sticky situation of trapped moisture in wood and ensure the longevity and quality of their projects.
Free Download – 6 Reasons Your Wood Project Failed
When Is Wood Wet or Dry?
If a living tree has just been cut, it’s wet. That’s a guarantee. After that, any rule of thumb will be no more than an estimate.
While many guides or tables are available to help identify the correct MC for a wood species or a geographic region, ultimately, MC is best monitored with an accurate wood moisture meter.
Even within one geographic area, temperatures and ambient humidity can vary. In interior installations, the operation of the HVAC system will play into the wood’s MC levels.
Wagner Meters’ wood moisture meters give you fast, accurate and easy-to-operate assessments of wood MC. Their non-damaging pinless technology even lets you “scan” many board feet of lumber to help identify potential wet spots or changes within the wood stock or 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 MC in context. The natural give and take in 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 an MC level that is too high or too low for conditions.
Shop Orion Moisture Meters
Tony Morgan
Tony Morgan is a senior technician for Wagner Meters, where he serves on a team for product testing, development, and also customer service and training for moisture measurement products. Along with 19 years field experience for a number of electronics companies, Tony holds a B.A. in Management and his AAS in Electronics Technology.
Last updated on November 7th, 2023
