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Whether you’re drying your own mill-sawed wood or just working with pre-sawed lumber that’s been sitting outside for a while — and maybe got a little rain — the moisture content of the material you use may well make the difference between success and failure in your next woodworking project. But besides waiting around until you’re pretty sure the wood is “dry,” how do you know how moist your stock is? Easy: You apply a wood moisture meter.

The first time it really dawned on me that wood can hold varying amounts of water was when my father and I were off-loading some oak he picked up from a mill in Mississippi. It was finish-sawed, but not dried. (His intent was to dry the wood back at his house in Texas.) He bought just over 1,000 board-feet in the form of 12″ x 1″ (and some 2″) x 10′ boards. They were heavy. Seriously heavy. As in, the two of us could just about pick up the 2″ boards and the 1″ boards were difficult.

A couple of years later we moved the lumber from where we originally stacked it to another place about 40′ away, and guess what? It was significantly lighter. Besides the length, each of us could easily pick up the 1″ boards, and the 2″ boards were easy for the two of us. The wood had dried that much, even just sitting under an open-around-the-bottom tarp.

Sadly, my father never got around to doing anything with the pile of oak before he died, though it’s now resting in a safe place waiting for Sean to take a run at it with his soon-to-be-installed planer. So when I saw the low-buck moisture meter (pictured) in the tool corral at the local big box, it reminded me of the whole process.

The meter seems pretty simple: It measures the resistance between the two conductive prongs, interpreting the result in terms of moisture content. (In fact, I’d bet this works in a surprisingly similar fashion to home body fat percentage testers.)

But I’ve got a few questions that maybe some of you more experienced Toolmongers can answer. Do the cheap meters like this suffice for woodworking purposes, or would one require more accuracy than they can offer? I noticed that the Amazon reviews for the one above, while all pretty positive, indicate that purchasers are using it for other purposes, like detecting the extent of water leaks or checking to see whether firewood is dry enough to burn.

A quick look around the ‘net shows that wood moisture testers start around $13 and run up to around $150. Admittedly, the $150 models look a good bit more carefully-made. But are the electronics that more accurate?

Digital Moisture Testers [Google Shopping]
Via Amazon [What’s This?]

 

12 Responses to How Moist Is It?

  1. A1cntrler says:

    When we recently sold our home, the home inspector also used on of these to probe the drywall around and below our shower area to check for moisture. Also saw him probing the trim on the outside of the house with it. No moisture problems were noted on the inspection, however I did not see him with a tube of caulk filling his probe holes on the bottom of my old windowsills.. Guess the new owner may see a problem develop later on…

  2. DoItRite says:

    I bought one from Harbor Freight a few years ago that is nearly a dead ringer to this one. Bought it for determining how dry some softwood flooring was before installing. When I bought the flooring it t was around 30 percent, and if I remember correctly under 15 percent a few months later when I installed it.

    I would have waited longer, and probably would have had a tighter floor if it dried longer, but ny T & G flooring was starting to twist and cup, so I decided to put it down while I still could.

    I don’t know how accurate it was, but it seemed to measure something. I dont even know how you could tell how accurate it was unless you could compare the measurement with some wood measured in a laboratory.

  3. fred says:

    General has been venturing into several new areas since they acquired Mannix about 4 years ago. Instruments like this one are the result. There has been a bit of debate about pin versus pinless moisture meters. We switched over to pinless Wagner meters several years back – have not done any exhaustive testing or side-by-side comparisons – but just find the pinless Wagners convenient. Ithink I recall one of the magazines (maybe Fine Woodworking – not sure at all) comparing moisture meters.

    BTW Wagner “button sized” RH meters are very cheap, fast and convenient for testing concrete slabs

  4. rick says:

    these are so basic I am sure that a cheapie meter works fine. These meters are great for those of us who heat with wood to make sure it is properly dry before you toss it in the stove!

  5. uqbar says:

    About that wood being less heavy on the second move: maybe you guys just got stronger from moving it the first time! 😉

    Serious comment/question: Do these meters come with a chart or table to help determine the “correct” reading for different types of wood?

  6. B. Foo says:

    I’ve read postings from people who use these regularly (professional woodworkers) and while the expensive ones were nice, the Harbor Freight and other cheapies measured within 2% of the expensive ones. So, if +/- 2% is too great of a discrepancy then you might want to buy the expensive ones. Of course, I guess theres no way of telling if the expensive one or the cheapie was more correct, we just know they were a little off.

  7. rg says:

    I don’t think inaccuracy in the conductivity measurement with these devices is so much the electronics, as it is the inconsistency of the probe surface contact area. i.e., how hard to you push the probe into the wood. I’d guess that 10 different measurements would give you 10 different readings, regardless of the electronics. I’m assuming that these devices are temperature compensated. So, calibration aside, the readings will be somewhat relative.

    I think you correctly hinted at a more accurate method of determining moisture content in wood, that is, by it’s relative weight. Since wood will always try to achieve equilibrium with the relative atmospheric humidity, if you can control that, after a certain length of time, you’d have a good idea of the moisture content.

  8. Shopmonger says:

    Cheap is fine as long as you understand there will be a tad discrepancy amongst readings, but in the world of wood working there is no need for that level of accuracy in Moisture.

    1. There were no moisture meters in the 1800’s and yet furniture from that era still hold true.

    2. The Amish don’t use them….

    3. As for a chart…No because relative humidity in your area will determine the final amount that is tolerable to work with. I live in NJ and we have much higher humidity that say someone in AZ…so if you look at the relative humidity in your area, and then talk to some local guys they will give you what their readings are to determine a good working number for you.

    4. As a rule of thumb, if kept in a dry damp free environment, it takes one year per inch of thickness to dry to a good working moisture. (Use stickers to raise the boards apart for good air circulation)

    5. If buying kiln dried material, or for flooring it is recommended that there bee a week of acclamation time before using. For flooring i recommend it be in the room that it is to be installed in, and no the garage or the basement.

    ShopMonger

  9. fred says:

    @ Shopmonger

    Some of our nightmare jobs are ones where the client has pre-ordered most of the wood (wainscoting etc.) and has it all stored in their garage on a concrete slab.

  10. shopmonger says:

    Two things of the world that don’t ever dry…concrete and glass……

    yeah Fred gotta love that…

    Shopmonger

  11. Simon says:

    In response to a few comments here (they got by without them in the 1800s, just wait for a while and see if it weighs less, etc);

    You certainly can get by without a moisture meter, if you have time and space to store your lumber for long enough. I have a friend who has a home-mill. He’s got piles of logs (literally, at least 50 or 60 logs) waiting to be milled, and a barn full of planks drying. He sells some of it, to pay for his chronic woodworking habit, but for the most part, it sits and waits. For years. for decades. He has a moisture meter, but on most of the wood, he never uses it, because it has been drying for years, and he can remember the history of every stack of wood in the barn. It is as dry as it is going to get in that environment, and only needs to be brought inside for a week or two (assuming the finished product is indoor furniture).

    I, on the other hand, do not have wood coming out of my yin yang. I do not have endless square footage of barn-space to store stacks of drying lumber for decades. When I help my friend mill some wood, and he gives me some of it, I have a small corner in my yard under cover which I stack the wood in, and I don’t want to leave it there any longer than I have to. If it has been a dry summer, and I can bring the wood inside after just 6 months, I don’t want to leave it there for another 18 months “just to be sure”. I want to run it through the planer, and see how it looks (which is incredibly satisfying, to dress a piece of wood you first met when it still had bark!)

    -s-

  12. Amanda says:

    I just got an $8.99 one from amazon that I’ve been thoroughly impressed with.

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