Using a Moisture Meter

But once you start down the addictive path of less-expensive lumber sources, such as local sawyers or direct from the mill, you'll find you're stumbling into unknown territory with regard to drying. Use improperly or incompletely dried lumber in a project and you could be setting your future self up for a host of problems, such as warping or cracking, as the wood completes its acclimation. A moisture meter is your insurance against those problems, paying for itself by letting you know when that wood is ready to use.

If you're ready to take those first steps toward alternate lumber sources, read up on how to use this handy device. Then, check out Six Favorite Lumber Sources, below.

The handheld moisture meters typically used in woodworking come in two varieties. Pin meters measure a wood's moisture by means of pins pushed into the wood, while pinless meters have a flat sensor on their back.

Each requires that you first set it for the appropriate wood species to get accurate readings, above. Some meters require a correction for temperature, while others use built-in temperature sensors.

Pin meters require you to push the metal pins as deep as possible into the wood, above. Electrical current travels between the pins, measuring resistance and converting it to a percentage of moisture. These meters read only between the pins and only as deep as the length of the pins. Some meters have multiple depth-reading capabilities and come with short (1/4") and long pins (7/16"–1/2"), but pressing those pins into some wood species proves difficult. The pins leave holesbut they're usually difficult to see after sanding and finishing.

Pin meters don't require a smooth, flat surface, so they work better than pinless meters on irregular, wavy, or twisted boards. Meters with insulated pins (found on premium models) won't read surface moisture, while pins without insulation might, giving you an inflated reading. Some pin meters can be used with long probes or with probes attached to long wires for measuring moisture in a stack of lumber, above.

A pinless meter, as shown in the opening image, above, works best on flat boards because it needs the sensor plate on the back to rest fully on the wood. This meter uses electromagnetic waves to read the moisture level beneath that plate, typically deeper than a pin meter can, and scans more areas faster. A pinless meter leaves no marks on the wood. Dual-depth pinless meters test at two depths (often 1/4" and 3/4"), handy for use with thin and very thick boards. But a meter like this can also read through thinner boards into whatever is behind it, so elevate the board if it's not already on spacers. Surface moisture can prevent the meter from reading into the wood, so measure only where the surface is dry.

So which type should you buy? Both have advantages, and both work equally well when used correctly. The pin meter's ability to measure stacked lumber with multiple probes makes it more versatile, but the pinless meter works more quickly and without piercing the wood. Meters with more features often come with a premium price (up to $500). Our advice: Don't skimp on a cheap meter that will likely be limited. Spending at least $100 should get you a meter that works well and leaves your eyes free of excessive moisture in the form of tears of regret.

As with any tool, a moisture meter works well only when used properly. Follow these tips to ensure you'll get reliable readings.

* Take readings in several places near the edges as well as the along the center of boards. Use the highest reading as the moisture level for the board.

* For boards thicker than 3/4" (or your meter's depth range), measure from both faces to get the most accurate overall reading.

* When using a pin meter, look for places to insert the pins that won't mar the best surfaces of the board.

* If you take the meter with you to your lumber source, bring along a spare set of batteries.

* When buying any lumber, especially dimensional spruce/pine/fir (SPF), stack it and let it acclimate to your shop's temperature and humidity for a week or two before working with it, above. Check the moisture level upon arrival and every 4-5 days until the EMC is acceptable.

* When using a pinless meter, sand or plane several flat spots on boards to ensure an accurate reading, above. If you're working away from home, bring along a small hand plane or a battery-powered belt sander or power planer to do this.

* When not in use, store your meter in its case or pouch, above, to prevent damage. Store it in a cool, dry environment, away from extreme heat and cold that can damage it. Keep the owner's manual and species chart in the pouch as well.

* Readings around knots and interlocking grain will tend to be higher than regular grain until the wood reaches its EMC. So if the rest of the board is at an acceptable moisture level and you don't plan to use the knotty or figured grain, you can use those drier portions right away.

* Each meter is designed to read moisture within a given range. Most are about 6–30%, but more deluxe models can read higher. Most woodworkers can get by with the lower range.

* If you're checking on a stack of lumber that's still drying, log the readings to track the progress. High-end meters with Bluetooth can share this data with an app.

* Avoid setting wood directly on the floor, especially on concrete, because the wood will take on moisture. Instead, stack the wood on spacers.

No matter when it was cut or where it came from, wood will always have a level of moisture (expressed by percentage) within its cells. Before you can use it without concerns, wood must be dried, either in a kiln or air-dried, or a combination of both. Once wood dries to the point that its moisture percentage "levels off" with the environment around it (humidity level and temperature are the biggest factors), it will have reached its equilibrium moisture content (EMC). This means it will stop losing or gaining moisture and will remain at that level until the environment changes, such as transitioning from summer to winter; moving from one geographic region to another; or even moving from a space without climate control into a building that has heating and cooling.

The ideal moisture level of wood depends on where you live. As seen in the U.S. map above, the dry climate of the Southwest naturally makes lumber dryer than it would be in the humid Southeast, while the rest of the country goes through similar seasonal changes. Ideally, lumber should measure 6–11% moisture content to avoid problems such as warping or shrinking as you begin milling it and building.

If you buy wood from any of these sources, you'll want to have a moisture meter to know what you're getting: