Achieving the Best Accuracy From Your Moisture Meter
A moisture meter is a small device that fits in the palm of your hand and is used to measure the moisture content in lumber or other wood products.
Moisture meters are tools used by wood products manufacturing quality control personnel, professional woodworkers, serious hobbyists, wood flooring installers, and others. Moisture meters are important because too much or too little moisture can cause serious problems.
How Accurate Are Moisture Meters?
Moisture meters can be accurate within 0.1%. Well… that’s kind of stretching the truth a little and let’s explain why. What is accurate is that high-quality moisture meters have a 0.1% repeatability rate. This means that if you take many readings — one right after the other — of the same piece of wood, the moisture readings will be within 0.1% of each other.
Also, a high-quality meter’s digital display is accurate to within 0.1% of what the meter’s interior electronic technology determines to be the wood’s moisture content. In simple terms, what you read on the meter’s display is a faithful representation — to within 0.1% — of the moisture content the meter is reading.
At Wagner Meters, we believe in being open and honest about what moisture meters are capable of doing. It’s no secret that university studies have shown our moisture meters to be the most accurate. We’re not here to mislead anyone and this is why we encourage all our customers to take a look at this scientific research for themselves.
Why Accurate Moisture Content Readings Are Important for Woodworkers
Accurate moisture meter readings are important because wood is hygroscopic. This is a fancy way of saying that wood is essentially a sponge. That is, it will both absorb moisture from its environment and release moisture back into its environment. This process continues until the wood eventually comes into balance with its environment and is no longer absorbing and releasing moisture. We call this balanced state, wood’s Equilibrium Moisture Content (EMC). How long it takes wood to reach its EMC depends on a variety of factors. However, it will always happen.
Woodworkers — both pros and serious hobbyists — avoid working with wood until it has first reached its EMC. This is because wood’s physical size changes as it absorbs and releases moisture. When wood absorbs moisture, it expands. When it releases moisture, it shrinks. If you work with wood before it has reached its EMC, you risk ruining your project. This is because the wood will continue to absorb and release moisture (and thereby expand, shrink, warp, twist, or crack) even after your project is complete. The result will be a deformed project.
All woodworking professionals and hobbyists need to use an accurate moisture meter to ensure the wood has reached its EMC prior to constructing their projects. Inaccurate readings are not helpful, and can even be harmful to your projects.
How to Get the Best Accuracy From Your Moisture Meter
The accuracy of moisture meter readings depends, above all, on the quality of the meter and its proper use. Used properly, Wagner moisture meters offer accurate and repeatable wood moisture content readings. Inexpensive moisture meters often don’t.
However, even the best moisture meter won’t be able to provide accurate measurements if it’s not properly calibrated. While other manufacturers of moisture meters offer calibration blocks that allow you to determine if your meter is in or out of calibration, you will still need to send it back to the manufacturer to be recalibrated. However, Wagner’s Orion® series meters come with an On-Demand Calibrator that allows you to recalibrate the meter back to factory standards yourself, in the field.
Our Orion 950 also has Bluetooth® connectivity to apps and can calculate the EMC, relative humidity, and ambient temperature.
What Are Acceptable Moisture Readings?
An acceptable wood moisture meter reading will, of course, vary according to a variety of factors including the geographical location where the tree was grown. However, we can say the following…
- Wood used in the construction of building frames normally has a moisture content from 12-19%.
- Wood used to construct furniture intended to be used indoors normally has a moisture content that should usually be from 6-8%.
Two Types of Moisture Meters
There are two types of moisture meters, pin and pinless. We’ll go over the basics of each, including how they work and things you need to keep in mind when using them.
Pin-Type Moisture Meters
Pin moisture meters have two small probes that must physically penetrate the wood in order to obtain a moisture reading. When the meter is turned on, an electrical current passes through the pins and measures the moisture content in the path of least resistance between the pins only.
The technology behind pin meters is based on the fact that water (with salts and impurities) conducts electricity, while wood doesn’t. The wetter the wood, the less resistance there is to the current.
Pin-type moisture meters are very sensitive to wood temperature. This is why they should always come with temperature correction charts or adjustments that you’ll need to use to ensure your readings are as accurate as possible.
Of course, any measuring instrument, including ours, could give inaccurate readings (or not work at all) if the operational temperature of the meter is outside its specified range. For example, if you leave your meter sitting in the hot sun for several hours and then take it into an air-conditioned room and immediately start to use it, your reading might not be accurate. You should allow the meter to cool down first. (The temperature charts that come with pin-style moisture meters are for the wood, not the meter.)
Pin meters are also sensitive to wood’s chemical makeup and because this varies from species to species, they will ask you to enter the type of wood before taking a reading.
Another thing to keep in mind about pin meters is that they’re susceptible to drift at low moisture contents. In other words, the reading might change before your very eyes. Some manufacturers of pin-type meters suggest taking the reading immediately before this has a chance to happen. However, that might be hard to do in some cases.
Finally, if you’re using an external hammer probe to perform deep readings, be careful of how you hold the hammer’s cable. There’s an electromagnetic field around it and if you hold it the wrong way, the meter’s accuracy can be affected by up to 2%.
Pinless Moisture Meters
Pinless wood moisture meters have an electromagnetic sensor plate that allows them to measure the moisture content of wood without poking holes in it. This makes pinless meters excellent for measuring the moisture content of fine wood furniture and flooring.
Pinless meters are sensitive to wood density, or ‘specific gravity’. Because this varies according to species, pinless meters will ask you to enter the wood’s species or specific gravity before you take a reading.
Both pinless and pin-type meters are sensitive to surface moisture and the usual manufacturer recommendation is to wipe the moisture from the wood and then wait for around 30 minutes before taking a moisture measurement reading.
How to Use a Wood Moisture Meter
- Turn the meter on and enter the correct settings.
- Push the pins carefully into the wood. Be careful not to bend or break them. Keep in mind that the denser the species, the harder this will be.
- Take a reading.
- Repeat, if necessary. Remember, if you’re testing the moisture content of anything except a very small piece of wood, you’ll need more than one reading in order to get an accurate picture of the wood’s moisture content.
- Turn the meter on and enter the wood’s specific gravity.
- Place the meter on the wood surface and take a reading.
- Move the meter along the wood piece to take subsequent readings. A good rule of thumb is one reading per foot along the length of the piece.
- Repeat until you get a picture of the wood’s moisture content.
Can a Moisture Meter Reading Be Wrong?
Yes, absolutely. A moisture meter reading could be wrong for a variety of reasons including, but not limited to…
- It’s out of calibration.
- The wood’s surface is wet.
- You’ve entered the wrong wood species.
- The meter has been damaged.
- The pinless meter’s scanning plate has been damaged in some way and this is affecting its ability to make proper contact with the wood.
- The pins on your pin-type meter are bent, broken, or rusted.
- There are flaws in the wood such as knots in the area of reading that are affecting the wood’s specific gravity (density).
- The meter’s batteries are low.
When it comes to taking accurate moisture meter readings we can’t stress enough the importance of studying the user guide that comes with your meter to ensure that you’re using it correctly.
How to Check a Moisture Meter for Accuracy
Moisture meters that are out of calibration do not provide accurate readings. Quality moisture meter manufacturers sell calibration blocks that allow you to test if your meter is in calibration or not. (Be sure to use a calibration block intended for your specific meter.)
All Wagner Orion moisture meters come with an On-Demand Calibrator that allows them to be instantly recalibrated, no matter where you are.
What to Do If Your Moisture Meter Is Out of Calibration
Unless you’re using an Orion meter, you’ll need to send the meter back to the manufacturer for recalibration. You’ll find information about this in your meter’s user guide.
Why a Quality Wood Moisture Meter Is Important
As we noted above, we measure moisture content in wood because wood is hygroscopic and we want to make sure it has reached its EMC before we start working with it. In other words, we want to make sure it’s neither too dry nor too wet.
Therefore, it goes without saying that accuracy is the single most important feature of any wood moisture meter. An inaccurate meter isn’t good for much of anything. However, keep in mind that even meters of the highest quality are affected by a variety of factors including the wood’s density, wood temperature (important for pin-type meters), and chemical makeup (pin-type). If these factors aren’t taken into account, even a highly accurate moisture meter can produce inaccurate results.
What we’re trying to say is that even the best moisture meter must be used properly to ensure accurate readings.
As Sales Manager for Wagner Meters, Ron has more than 35 years of experience with instrumentation and measurement systems in different industries. In previous positions, he has served as Regional Sales Manager, Product and Projects Manager, and Sales Manager for manufacturers involved in measurement instrumentation.