How to Measure Moisture in Wood Without a Moisture Meter
Imagine that you’re about to start a new woodworking project—it might be a handcrafted table or another piece of furniture.
You’re excited as you anticipate what your slab will become!
The wood has been acclimating for some time now, and you’re quite sure it’s at the right dryness. But to be sure it’s dry wood, you reach for your wood moisture meter.
As you get ready to press the meter against the slab, you notice a crack on the contact plate. That can’t be good news! And sure enough—the meter refuses to give a reading.
Now what? You call the manufacturer, and they promise to send you a replacement, but until then, you’re without an essential tool. Is there any way to determine the moisture content of wood without it?
Maybe this isn’t a hypothetical scenario for you.
You might be on this page for a similar reason. Your moisture meter may be broken or lost. You may be waiting for repairs. Or, you just don’t have a moisture meter yet.
Keep reading to find the answers to the following questions:
Why measure the moisture content of wood
Measuring the moisture content of wood is key to having a finished product that remains damage free for years to come. Otherwise, you may be setting yourself up to lose money, time, and possibly your reputation as a woodworker.
The reason is that wood products, which are hygroscopic materials, shrink and expand until they have the same amount of moisture as their environment. If the wood is drier than the environment, it expands as it takes on moisture. But if it’s wetter, the wood dries, shrinking in the process.
When first cut, wet wood (also known as green wood) begins to lose moisture as it dries. If air-dried, it can take a year or two to reach proper dryness for a project. Kiln drying can speed up this process.
But if the wood is used before it has been properly dried, it may continue to experience shrinkage. The result is a project that may warp or change shape. It won’t look as beautiful as it was when first built.
You may not care so much about certain outdoor projects—a deck, a playhouse, or the framing for your house. And certain types of wood species are less affected by changes in moisture content. Species such as mahogany, white oak, and teak.
That’s why woodworkers for these projects are aware of the equilibrium moisture content (EMC) in their region, which is based on the temperature and relative humidity. They always double-check that the moisture level of their wood matches that number.
So resist the temptation to skip measuring moisture content!
And using your hand to feel the wood won’t cut it, either. You’ll definitely be setting yourself up for errors that way.
One of the most accurate ways to get the moisture readings of wood is to use a wood moisture meter. But if you don’t have one for some reason or another, we’ll look at some alternatives.
How to measure moisture content without a meter
The ASTM (American Society for Testing and Materials) provides a standard for determining the moisture content of wood. Standard D4442 mentions two methods that can replace a moisture meter: the oven-dry method and the distillation method.
The oven-dry method
The oven-dry method involves drying a small sample of wood. The difference between the weight of the wood before drying and the weight after drying is used to determine the moisture content of the wood.
Let’s walk through it step by step:
- Take a small sample from the wood you want to measure. The piece of wood should be small enough to fit inside the oven. Weigh the wood. ASTM D4442 specifies the level of precision this scale needs to have.
- Put the sample piece into an oven that is between 215° F and 220° F (102° C and 105° C), as specified by the National Wood Flooring Association. Again, ASTM D4442 provides guidelines: The oven must be a “forced-convection oven that can be maintained at a temperature of 103 ± 2°C throughout the drying chamber.” It must also have a way to allow the moisture to escape.
- Check the wood every few hours and weigh it. Continue to dry the wood until the weight stops changing during the 4-hour intervals. Ideally, it shouldn’t change more than 0.1%.
- Weigh the wood again.
- Calculate the moisture content using the following formula:
This method may be an option for you if you have no other way to measure moisture content. However, it also has many downsides.
For one, it requires specialized tools, including a very accurate scale and a wood oven with proper ventilation. If you don’t have them already, these tools could cost you more than a quality moisture meter.
Another downside is that the process can be tedious and time-consuming. It may take just as long as waiting for a moisture meter repair or ordering a new one.
When you use the oven-drying process, you also have to consider the waste involved. The sample piece of wood will be destroyed and unusable.
And finally, there’s the question of accuracy. After you go through all that work, will you really know the moisture content of the whole piece of wood? Remember, you only put a sample in the oven—there could be variation in the rest of the wood, particularly if you took your sample from the outer edges rather than the middle.
So what’s the other option?
The distillation method
The distillation method is used in laboratory settings for measuring the moisture content of wood that has been “chemically treated or impregnated.” It works for wood containing preservatives or chemicals that could affect the accuracy of other methods.
For this option, you would take a sample piece of wood and cut it into chips—about 20–50 grams worth. Those chips are placed in a flask that is heated. Then, you would add some kind of chemical solvent, typically either xylene or toluene, into the flask. The solvent causes the water in the wood chips to evaporate, and a cooler outside the flask condenses the water. The condensed water can then be measured to determine how much moisture was in the wood chips.1
But you may be wondering, is this process realistic for a woodworker?
It really isn’t.
You’re probably not a scientist, which means you aren’t going to have the specialized items on hand—a flask, a chemical solvent, and a special cooler for condensing the water.
So why not stick to quick and easy meter readings without all the extra hassle?
Why a moisture meter is the best option for moisture measurement
Alternative methods of moisture measurement, such as oven-drying or distillation, are usually not practical options, particularly when you need a “quick fix.”
A quality meter is going to give you the quickest and most accurate readings without requiring you to have a lot of other equipment on hand.
So, do what you can to find that lost moisture meter, get your moisture meter repaired, or buy a new one. You won’t regret the effort.
And if it’s your first time shopping for one, you’ll have to decide whether a pinless moisture meter or a pin-type moisture meter suits your needs best. Check out our buying guide for tips on what to look for.