The Moisture Content of Wood Is Important. Very Important.
It doesn’t matter if you’re a professional who makes a living installing fine hardwood floors or a weekend hobbyist. Anyone who works with wood needs to know its moisture content. Here’s why…
Wood is a hygroscopic material. This means it both absorbs moisture from its ambient environment and releases moisture back into its ambient environment. In other words, wood is something like a sponge.
And this can be a problem for anyone who works with it because…
As wood absorbs moisture, it expands and as it releases moisture, it shrinks. Wood expands or shrinks about 1% across the grain for every 4% change in moisture content. (Wood doesn’t shrink or expand much along the grain.)
Although a 1% shrinkage or expansion might not sound like much, it can cause serious problems with any wood project. This includes everything from small projects created by a hobbyist to expensive hardwood floors installed by a professional. Problems like gluing, cabinet doors and drawers that don’t open and close properly, or the cupping, crowning, and buckling of hardwood floors.
No serious woodworking pro, cabinet maker or hobbyist wants to spend time working on a project only to see it ruined later if the wood starts to shrink or expand.
So, what’s the solution? How do we guarantee this won’t happen to our wood projects? Let’s find out…
Wood Must Be Allowed to Reach Its Equilibrium Moisture Content
Given enough time, every piece of wood will eventually reach the point where it’s no longer absorbing moisture from the environment or releasing moisture back into the environment. At this point, the wood is in balance with its ambient environment. This is called the equilibrium moisture content (EMC) of wood.
All wood used in projects must be allowed to reach its EMC before construction starts. Wood should also be kept at its EMC during construction. If you don’t do this, after construction, the wood will continue to absorb and release moisture – and consequently expand or shrink — until it reaches its EMC. The result will be doors and drawers that don’t fit properly, deformed flooring, etc. Therefore, you don’t want to waste your time building projects from wood that hasn’t yet reached its EMC.
So, how do you know if the wood you want to work with has reached its EMC? You use a moisture meter, and that’s what we’re going to talk about next.
How to Properly Use a Wood Moisture Meter
Measuring moisture with a wood moisture meter isn’t difficult. You just need to follow a few simple rules…
Read Your Manual
When you first get your new moisture meter read through the manual carefully. It contains information about how to use the meter and information about how to use the species settings. Also, don’t forget where you placed it. If possible, keep it with the meter.
Use the Right Meter for the Job
You also want to make sure you’re using the right meter for your particular job. Some meters work well with both thick and thin pieces of wood while some meters are designed to work better with thin pieces of wood. Some meters need a flat surface to take a reading. If you need to measure moisture on round stock, you need to choose a meter that can do that.
If you need to analyze your data, look for a meter that’s capable of collecting data.
Set Your Meter to the Right Wood Species
Your moisture meter comes with information that allows you to adjust the moisture sensor according to the species of wood you’re measuring. It’s important to use it if you want an accurate reading.
Wipe any Visible Water from Both the Wood and the Meter
If there’s water or condensation on the surface of the wood, you’ll need to wipe it off completely and wait for about a minute before taking a reading. It doesn’t matter what type of meter you’re using, visible water on the surface of the wood will produce an inaccurate reading. In fact, pin meters with non-insulated pins will produce very inaccurate readings if there’s water on the surface of the wood. Keep in mind that if the water has already soaked into the wood, this will cause a higher moisture reading.
Any visible water or condensation on the meter itself should also be wiped off prior to taking a reading.
Beware of Concrete Subfloors
Keep in mind that flooring can pick up moisture from the subfloor and produce a higher moisture content reading. This is especially true when there’s a concrete subfloor. Wood subfloors usually aren’t a problem.
Don’t Take a Reading Near Metal (Pinless Meters Only)
Don’t take a pinless wood moisture meter reading near anything metallic. Pinless meters are very sensitive to anything that has the ability to conduct electricity, and if these objects are nearby, it could produce an inaccurate reading. If the piece of wood is small enough, you can hold it up in the air while taking a reading.
Apply the Correct Amount of Pressure to the Meter
If you’re using a pinless wood moisture meter, consult your meter’s manual to find out how much pressure you should apply to the meter while you’re scanning the surface of the wood with the sensor pad.
Keep a Supply of Fresh Batteries Handy
You never know when you might need them and if they’re not handy, you’ll need to stop what you’re doing and go get some. So, keep some spares on hand. Also, some meters will give inaccurate readings when the battery’s voltage drops near the end of its lifecycle.
Treat Your Meter Well
Your moisture meter isn’t indestructible. So, treat it accordingly. Don’t toss it across the room or let it fall into a pail of water. If you drop it or submerge it in water, it could suffer damage and if it does, it won’t give accurate readings. If it comes with a carrying case, use it.
If you follow these simple rules, you should be able to get the most out of your moisture meter. Now, let’s take a look at things you shouldn’t do…
A Few Things You Should Never Do with a Wood Moisture Meter
Don’t Use It On Concrete
A wood moisture meter was designed to measure the moisture content in wood only. If you use it on any other material, the readings won’t be accurate.
Don’t Try to Fix It Yourself
If your moisture meter isn’t working correctly, don’t open up the case to see what’s going on as this will usually void the warranty. First, check the manual that came with it or any online documentation, if it exists. There might be a solution to your problem that doesn’t involve opening up the case. If there isn’t, contact the manufacturer and send the meter in for service. If it’s still under warranty, it can be either repaired or replaced.
Don’t Assume It’s Waterproof
Moisture meters measure moisture, but that doesn’t mean they’re waterproof. If they suffer water damage, they won’t give accurate readings. So, don’t take your meter into the shower with you, hose it down, or clean it by submerging it in soapy water.
Don’t Use It Unless It Has Been Properly Calibrated
Proper calibration is essential if you want accurate readings. The manual that came with the meter will have information on how to calibrate it and how to tell if it’s out of calibration.
If you buy a quality meter, treat it well, and follow the rules, you shouldn’t have any trouble getting accurate moisture content readings.