How about setting level and plumb lines for a project? Are you still using a water level or transit for such applications? Probably not—the laser level has earned a place in the tool arsenal of most carpenters because it reduces both labor and potentially costly layout errors, thereby saving its owner time and money.

There’s another tool, which, while not yet very common on most jobsites I visit, has the potential to save you even more time and money than laser levels and nail guns combined. It’s a moisture meter.

What Moisture Meters Do

Moisture meters “read” the moisture content of lumber, drywall, concrete—in fact, just about any porous building product, whether already installed or sitting in a supplier’s warehouse. This information allows installers to accurately predict how the materials they’re working with will move in the future. This knowledge is invaluable, as one can then plan the installation accordingly and be secure in knowing they’ve made provisions for the inevitable expansion or contraction of the lumber, or whatever material they’re working with.

Moisture content varies dramatically. (Note: Click any image to enlarge.)

If you don't know the moisture content of the material you're installing, you're working in the dark, and luck isn't on your side.

Wood flooring installers have been using moisture meters for years. Many will check not only the MC (moisture content) of the flooring they’re preparing to install, but also the MC of the slab or subfloor it’s about to be installed over, and sometimes even the adjacent framing and drywall. This is especially true on new construction projects, where literally thousands of gallons of water vapor will most often evaporate from curing concrete, framing lumber, drywall compound, and paint.

The reason they take such precautions is simple—moisture goes to dryness. If the wood flooring is dryer than the surrounding materials, moisture from those materials will likely work its way into the flooring, causing it to swell, and possibly even buckle, in extreme cases. Conversely, if the flooring has a dramatically higher MC than surrounding surfaces, moisture will be drawn out of the flooring, causing it to shrink. Either situation is a likely call-back (and an expensive one at that), which is why installers often check and double-check conditions until they’re satisfied the MC of all the building materials—flooring, framing, masonry, etc.—in a particular area is similar.

But flooring contractors aren’t the only ones who can benefit from using a moisture meter. Anyone who works with finished products that have a propensity to move due to changes in moisture content will find value in owning an instrument. Finish carpenters, in particular, should carry a moisture meter in their truck and should use it just as flooring contractors do, checking and documenting the MC of not only previously installed components on the job, but all the millwork and cabinets delivered to the site, as well as any lumber taken from an outside source, such as a lumberyard, another jobsite, etc. In short, any material in your finished product that absorbs and releases moisture should be checked prior to installation.

What Moisture Meters Tell Us

Why go through all this trouble? Consider this… a 4% change in the MC of a piece of flat-grained softwood equals a 1% change in its size. This may not seem like a lot, but flooring installers know differently.

To put this into perspective, let’s consider a typical T&G beadboard installation, whether on a porch ceiling, as wainscoting on a wall, or whatever. Assuming 3-in. wide beadboard is being used, it will take 4 pieces, placed edge-to-edge, to cover one running foot on the width of the wall or ceiling. On an 8-foot wide surface, that equals 32 pieces. And if the MC of the beadboard were to increase 4%, that equates to over 1/32 in. of expansion per piece, or about an inch of total expansion, and that’s just in 8 feet! Imagine what happens when a beadboard porch ceiling runs perpendicular to a home!

While we can’t change how nature does her business, we can be aware of conditions and plan accordingly. Fortunately, you need not spend a ransom to acquire a decent moisture meter. There are entry-level models available for as little as $30, though one should probably plan on spending at least $125 and up to acquire a good quality instrument.

Pin or Pinless?

That’s the first choice you will need to make when selecting a meter. Most moisture meters read the moisture content of material through pins that are driven into the surface of the material. The pins are needle sharp barbs, typically around 1/2 in. long. The pins reach into the cells of the material, measuring the electrical resistance of the product. Since moisture is a good conductor of electricity, the greater the amount of moisture present, the higher the reading will be.

Pinless moisture meters typically bombard the material being tested with RF (radio frequency) signals, measuring dielectric properties which change proportionally to how wet or dry the material is.

The advantage to a pin-type meter is that it usually costs less than a pinless. I’ve owned a very serviceable Lignomat pin model for close to 15 years. If I recall correctly, I paid less than $100 for it. A disadvantage to this type of meter is that it’s a bit invasive, leaving two holes wherever it’s pushed into a surface (see image, below). While not very large, these holes can be an issue if the surface is already finished (as is usually the case with cabinetry, for example).

On the flip side, some instruments offer longer pins and even hammer probes for checking the MC of thicker lumber such as logs and timber. This method is very accurate, which is why these are usually the tools of choice for commercial lumber and millwork operations.

Pinless meters leave no holes, but are usually more expensive, with prices starting at around $200, and often selling for much, much more. So, if one can afford it, why wouldn’t a pinless meter be desirable? In a nutshell: Accuracy. Pinless meters scan a cross-section of material, and then average the readings to give you the MC. If more moisture is present on the surface of the material (which is easier for the meter to scan) vs. the core, the MC reading can be skewed.

Additionally, a pinless meter is most accurate when the surface it is reading is dead flat and at least as wide as the scanning portion of the instrument. If you need to determine the MC of a sizable piece of lumber, such as a post or beam, you’ll get a more accurate reading by using a pin type meter. But if you need to verify whether that load of pre-finished, custom mahogany frame and panel interior doors is ready for installation, go pinless.

Pin meters have another limitation. They won’t typically read MC under 6%, since material that is drier than that doesn’t have enough moisture present for the meter to detect. This shouldn’t be much of an issue for carpenters in all but the most arid parts of the country, as even the driest material we install is usually in a range above 6%.

If the aforementioned information still can’t help you select a type of meter, there’s always the combination, or dual option. Fairly recent to the marketplace, a dual meter offers the advantages of both types of instrument in one package. It allows the user to quickly scan the surface of the material using pinless technology. If more accuracy is required, it also functions as a pin-type meter, thanks to the probes incorporated on its leading end. This best-of-both-worlds tool usually has a starting price of around $400.

For 3/4-in. material, the pins should penetrate at least 1/4 in. into the wood. To get an accurate reading on thicker material, the pins must penetrate deeper.

This pressure-treated 4×4 was soaked and felt like lead.

Calibration

Some meters require manual calibration to ensure accurate readings, while others are factory-set and not adjustable. This issue reminds me of the “fixed vs. adjustable vial level debate,” with each side having its proponents as well as opponents. If you choose a meter requiring calibration, be aware that you may also need to purchase a calibration kit with the meter, and occasionally perform accuracy tests. My feeling is that this is probably overkill for most carpenters as the increased accuracy (if any) is likely not enough to warrant the additional expense and effort.

Settings

The more accurate moisture meters require the user to select the type of material being tested. Because not all wood has the same resistance properties, one must set their meter to a predetermined species group. My Mini Ligno, for example, lists over 20 different wood species in two different groups. Setting the meter to the group being tested is clearly outlined in the user manual for the instrument, and usually requires little effort. On my meter, it’s as easy as double-clicking a contact switch that’s between the pins.

In using a couple of the newer models from Lignomat, I was pleased to discover that the more recent entries from this manufacturer also make selecting the species group easy, as they use the same style contact switch as my old meter. I was even more excited to test a model (the SD) that had a setting for determining the MC of not only wood, but plaster and drywall, as well— something my old meter did not allow me to do. This is a particularly useful feature when solid wood paneling is to be installed over a newly finished wall surface, as the wall must be completely dry, or any remaining moisture is likely to wreak havoc on the fresh wood (especially if the backside of the material hasn’t been sealed).

Displays

Moisture meters are offered with one of three readout displays—LED, digital, or analog.

LED displays give approximate readings, rounding the MC number to the closest (typically even) number, and illuminate a light, or lights, on the meter that correspond with the number. Some models will illuminate two numbers, should the MC fall between them.

Digital displays, as the term suggests, provide a digital readout of the MC. Some of the more expensive meters even measure to the tenth of a percent! I found these displays to be the easiest to read, with no interpretation required. An additional benefit these displays share with LED displays is their ability to be easily read in low light conditions.

Analog displays use a scale along the lines of those on electrical test meters to display the MC. Some of the screens are a bit small, so those of us with aging eyes may find them a bit of a challenge to read. However, these displays are pretty accurate.

You Get What You Pay For

While doing the research for this article, it quickly became apparent that the old adage, “You get what you pay for,” applies here, as it so often does with tool purchases. I got my hands on a handful of different models of moisture meters from several manufacturers. Since I’d been using an old (by today’s standards) model for so long, I wondered what, if anything, I was missing in not having the latest technology. I also wondered if a bargain basement model would perform well enough that I could recommend it as an option to those who simply can’t, or don’t want to, shell out hundreds of dollars for a device that may not see regular use.

I looked at meters that ranged in price from $30 (yes, thirty!) to around $400. I checked them against each other for accuracy, ease of use, features, etc. In the end, I came to the conclusion that moisture meters are akin to personal safety equipment—something is better than nothing. Even the $30 model I tried was functional, and may well suit the needs of an occasional user. It didn’t have the accuracy, range, or capabilities of more expensive models, but one shouldn’t expect it to, given its ridiculously low price.

Conversely, I didn’t see the value in the $400 instrument for my needs. It appeared to be well thought-out, with wonderful accuracy, but I was perfectly satisfied with tools that cost half as much. I believe the lesson here is to carefully identify what your requirements are, then buy accordingly. If you need the capabilities of a more expensive tool, or just love owning fine instruments, a higher end model may be right for you.

When it was said and done, I decided to upgrade from my 15-year-old LED model to a newer version that is practically identical, though with a digital display. I appreciate the increased accuracy of the newer model compared to the old one, plus the digital readout is my favorite.

As a hardwood flooring installer, I have been using wood moisture meters professionally for over 30 years. To use these meters properly, you need to understand some fundamental properties about wood moisture content and how the various meters actually function.

First, let’s look at what defines the concept of moisture content (MC) in wood. Next, we’ll talk about how a moisture meter works. And, finally, I’ll share some of the fine points of using a moisture meter—along with a few tricks of the trade that improve results.

What is Moisture Content?

Moisture content may sound like a simple thing to understand and measure, but it’s actually a little complicated—and it’s not what many people think it is. Moisture content is the weight of the water contained in a piece of wood compared to its oven-dry weight. Therefore, the best method for determining MC is to perform an “Oven Test” by weighing the piece of wood and then placing it in the oven at 212F or 100C for approximately 24 hours. When the piece of wood stops losing weight, it is oven dry. Oven-dry wood is at zero moisture content. In the best-case scenario, the oven test takes 24 hours to determine the moisture content—and the piece of wood is destroyed. Not an option if you’re working on a jobsite.

How Moisture Meters Work

Pin-type moisture meters measure the electrical resistance between two electrodes. When water is present in wood, electricity is more easily conducted, but as wood becomes dryer it resists electrical flow. This resistance is measured in OHMS. You can buy an ohm-meter from Radio Shack that measures the same property. About 20 years ago, Fine Woodworking published a set of plans with details on making your own electrical resistance moisture meter, but with the cost and availability of moisture meters today, making your own isn’t necessary.

Using Moisture Meters

Here are a few tips that should make it much easier for you to use a moisture meter accurately:

• The pins should line up with the longitudinal axis of the wood—in other words, with the grain, not against the grain.

• Touching the pins to the surface of the wood doesn’t work. You have to insert the pins to a depth of 1/4 in. to get the MC of a piece of 3/4-in. thick lumber.

• The pins don’t give accurate MC readings in end grain.

• The surface of the wood needs to be dry. A wet surface will give an erroneously high MC reading.

• In a pinch, you can use finish nails as electrodes. Insert the nails and touch the pins of the meter to them.

• Use a drill to prepare holes for inserting pins into very hard species like Ipe, Cumaru, Brazilian Cherry, Lignum Vitae. Regular pins will break or bend.

• Select a moisture meter with simple controls and an easy to read display. I use the Delmhorst J-4 and BD-10 models. These models are scaled to reflect the moisture content of Douglas Fir, which is the reference species used by the wood science industry. Over 50 years ago, wood scientists studied the relationship between electrical resistance and moisture content and published data for many different species of wood. It is this data that is used to calibrate current pin-type moisture meters.

Keep It Simple 1: The analog models I use are less expensive than Delmhorst digital models. But whatever meter you chose, take my advice, rather than spending money on additional features, invest in a copy Understanding Wood, by Bruce Hoadley, or the Wood Handbook, published by the USDA, Forest Products Laboratory.

Keep It Simple 2: Adjustable moisture meters, which can be set for different species, add another potential source for errors: it’s easy to set the meter for the wrong species, and it’s even easier to forget to reset the meter.

Keep It Simple 3: Because most moisture meter scales are set for Douglas Fir, corrections are necessary for other species. I make corrections manually, but those corrections are usually under 2%—not enough for most carpenters or woodworkers to worry about.

One last bit of advice: keep a spare battery with you.

AUTHOR BIO

Howard has operated Brickman Consulting, a consulting and wood floor contracting business in the Boston area, since 1984. Though his background is wood science—he spent three years as the graduate teaching assistant in the Wood Anatomy Lab at the University of Massachusetts, Amherst—Howard has always preferred the hands-on part of the business—installing wood floors and helping the industry understand wood-floor failures. Howard designed and manufactures the Slab-Safe concrete moisture meter. When he’s not working on a floor, Howard is particularly fond of Speyside Scotches and Welsh Corgis.

I love making things out of wood. That’s why I’m a carpenter; that’s probably why you’re a carpenter, too. So it shouldn’t come as a surprise that, with a little spare time on my hands, I went looking for a woodworking project.

I’ve specialized in stair building for most of my career, and for more than ten years, I’ve been writing about and teaching carpentry, too. Last fall, just as I finished setting up my clinic at the JLC LIVE! show in Seattle, a stack of boards a few booths away caught my eye. The Western Red Cedar Lumber Association was setting up a demonstration, and they had some beautiful old-growth redwood. I asked nicely, and they let me take 5 ft. off the end of a 2×8. The piece was almost perfectly quarter-sawn, with extraordinarily close grain, and just about totally clear. I counted 30 rings to the inch—that 2×8 took 240 years to grow! What could I make out of it? I had a nice set of tools, mostly donated to the clinic by my sponsor Festool. And I had my trusty spokeshave, which I use to fair the joints between handrail fittings.

Most carpentry consists of cutting up boards and moldings, and rejoining them into bigger things like doors, windows, bookcases, and floors. Carpenters rarely get a chance to get under the surface of wood: The sawmill finds a board inside a tree; the mill-shop finds a molding inside a board; but most carpenters only rip boards to width and cut moldings to length. Most carpenters don’t even know that the real glory of wood happens when we cut curves, when we make wood bend, when we carve into the heart of a tree and find the magic inside.

A few weeks before that show, I spent a Saturday afternoon canoeing and picnicking with my wife, Helen, and some old friends. We had a lot of fun. It was a sunny, colorful fall day. Not many motor boats. Calm enough so we could talk as we paddled around the lake. I have an old yard-sale wood-and-canvas canoe, a little leaky, but eye-catching, like a classic motorcycle. I love that canoe, but I’ve never liked the paddles. One is plastic and aluminum; the other is a glue-up from mismatched strips of wood, machine-carved to a graceless hunk. To my eye, those paddles never shared the same design or spirit as the canoe—strong only where it had to be and light where it could be.

I’ll never forget the paddles my Dad had when I was a kid. Maybe he had them since he was a Boy Scout in the late thirties. I think my brother has them now (he doesn’t get all the good stuff: I got Dad’s Ford tractor). Those paddles were carved from basswood, or Doug Fir, light colored, and lightweight. The blades were thin and rounded, the handles cut to fit the shape of a hand. Even then, my small hands could hold one of those paddles for hours. And the throat, where the shaft flairs out into the blade, was gracefully strong, and comfortable, too.

Somehow, I just knew there was a perfect canoe paddle inside that piece of old-growth 2×8 redwood.

A canoe paddle is supposed to be as high as your armpit, or maybe it’s your nose—I can’t remember. Anyway, I cut the board off at 58 in., (I’m no giant). Next, I held my tape measure as if I were paddling (see photo, above, right), and figured the shaft should be about 44 in. long.

First I traced the inside of my fist to get a good idea of how thick the handle or shaft should be.

Then I set my combination square at 3 in. and drew lines down both sides of the board for a 1 1/2 in. wide shaft.
Next, holding the pencil in my hand with about 4 in. sticking out, I let my wrist be a compass and drew the curves of the blade—out to the full width of the board and back again at the end.
Tightening up my wrist and the pencil, I drew the smaller radius of the handgrip.

My drawing wasn’t as symmetrical as I wanted, so I picked the best side and, using my saber saw, cut one side of the paddle to the line.

I picked up the piece that fell off and used it to improve the line on the other side. There is no better way to guarantee symmetry.

What was left of that 2×8 looked pretty funky when I held it up, but there was definitely a paddle in that piece of redwood.

I wanted to put a little bend in the design, so the blade would be vertical in the water right at the middle of the power stroke. I also wanted to make the paddle slightly hollow on the back side—like your hand when you’re swimming the crawl. I figured that hollow would give it a better grip on the water. I’d seen racing paddles with similar designs. With 1 3/4 in. of wood, I had some extra material to work with. The thickest part of the paddle, the handle, needed to be 1 1/4 in., so I could work almost 3/4 in. of bend (and a lot of hollow) into the blade!

The quickest way to remove wood is with a power plane. Both the Festool HL 850 and the EHL 65E work great for the job. The smaller plane can be held easily in one hand. Even with these planes set to cut the maximum depth (about 1/8 in.), the dust collector sucks up almost all the chips. First, I planed the ends of the paddle on one side, and the middle on the other side to put in the bend.

Next, I cut a hollow on the concave side of the blade, and tapered the other side as much as I dared.

The whole planing process took only about 5 minutes, and the paddle was quite a bit lighter when I finished. The final shape had to be cut with a spokeshave, then cleaned up with sandpaper.

The spokeshave is one of my favorite tools. We use them in my shop a lot, to make curved handrail parts. A spokeshave is really just a very short hand plane with handles on the side. The one I used here is a Stanley or Record Model 51, available from almost any good hardware store. Often these tools need some work before they can be used. I always grind the chip breaker back at about a 45-degree angle, which provides a bigger opening for the chips to pass through. A belt sander will do that job in less than a minute (see photo, above). I also sharpen the blade so that it will shave hair off my arm.

Like any tool, the spokeshave won’t do the job by itself. I’ve been handling these small planes for years; they’re as natural as riding a bicycle. But when I watched my friend Gary Katz try it for the first time—and he stubbed the plane repeatedly into the grain—I remembered that its not as easy as it looks. Here are a few tips:

Adjust the tool carefully. Set the blade adjustment screws so the shaving is paper-thin and perfectly even. Because the sole is so short, spokeshaves can be used to make surfaces flat or curved.

Keep the sole flat on the work. Hold the tool down hard, and don’t rock it while cutting.
Cut out of the grain or diagonally across it, otherwise you’ll stub the plane in the grain or jam the throat with shavings.

Plan ahead. Take off just the wood that has to be removed. Imagine the shape within the board. The tool is amazingly fast—even if each stroke removes only a 1/64 in., 16 quick strokes will remove a 1/4 in. in about 16 seconds!

First, I shaved the corners off the shaft to make it octagonal, then took those corners off to make it almost round. Then I shaved the blade on the concave side to get the shape I wanted; then on the other side to get the right thickness. The blade is only about 1/4 in. thick on the edges for lightness, and about 3/4 in. thick in the center for strength. I kept putting my eyeball on it to check for straightness. I also held the paddle an arms-length away, to check for symmetry. I paid special attention to the throat, where the blade meets the shaft: that transition must look right, and it must feel right, too—that’s the spot I’ll always be holding while paddling.

To work the handle, I clamped the blade end down and supported the handle against my leg. I checked the shape of the handle with my eyes closed—trusting that my hand would know the right shape better than my eyes. The faces of the handle are deeply concave, so I extended the blade of the spokeshave out more in order to reach the bottom of the hollow cuts.

The spokeshave took the paddle down to its final weight and shape. And it left a pile of shavings on the floor—the only real mess I made! Everything else was in the vacuum.

Sanding was the last step, and the Festool sander picked up that dust, too. I used the sander to take down the ridges left by the spokeshave, and to smooth out the pick-outs where Gary shaved the grain in the wrong direction. The Rotex cuts pretty fast. I probably could have started with a coarse grain paper, like 50-grit Crystal, and done a lot of the carving with the sander, too. Festool’s Crystal paper is an open grit that won’t clog while sanding paint or softwoods. I was able to smooth out the paddle pretty well with 80-grit Rubin, Festool’s normal sandpaper for wood. I took out the fine scratches with 120-grit.

For hand sanding I went back to #80, using a full sheet folded into thirds the long way to make it stiff enough for fairing. I sanded long strokes with the grain, to take out some flurbles that were easy to feel with the sandpaper, but were hard to see while machine-sanding. I used the #80 to break the sharp edges of the blade, too, and rolled it into a hollow curve to even up the rounded-over shape of the top of the handle. Then I went over it again with 120-grit paper, and then 180. The 180-grit polished the wood ’til it was almost shiny, but it also showed up some scratches and low spots that I hadn’t seen with the coarser grits. I went back to 80 to fix a few spots, then 120, then 180 again. With the sanding complete, the paddle was ready for finishing.

Spar varnish has to be the best finish for a paddle: after all, spars are wooden sailing ship masts, booms, and yardarms. I bought a pint at a nearby paint store along with a couple of foam throw-away brushes, a sheet of 400-grit waterproof paper, and a tack cloth. I blew the dust off the paddle, and laid the varnish on with the grain, everywhere except the handle. The handles are always left raw on old paddles, probably to improve the grip, but also because the finish would wear off anyway.

I hung the paddle up to dry with a spring clamp gripped on the handle. In all, I put on three coats of finish, sanding between each with the 400-grit, which I crumpled up under a running faucet, to keep it from clogging up with varnish. Between each coat, I wiped off the paddle with a rag and took the dust off with the tack cloth. I put the last coat on and let it dry in the least dusty place I could find.

Those of you who have attended my seminars and clinics might have noticed that I broke my Number One rule while making this paddle: Always design your work before you build it! But it still looks pretty cool. I’ll give it the real test this summer.