Moisture Meter

[Tim M Tuttle]

I bought this moisture meter from Lowe's the other day based on it's decent reviews and the fact that it was only $30.

https://www.lowes.com/pd/General-Tools-Instruments-Digital-Moisture-Meter/3136919

I will read 2x4s just fine but will not even register if I put it on walnut, maple, or any other hardwood. Anyone have this unit? Am I doing something wrong?

Can anyone recommend a decently priced moisture meter?

Thanks

[Will Boulware]

I've got a Mini Ligno and I can't recommend it highly enough.

[Steve Eure]

Tim, I bought that same meter from Lowes and have used it on maple, walnut and several other hardwoods with no problem. Are you making good contact with the pins? Be sure to press them into the wood, but not enough to break them. I mainly use it to monitor slabs that I am air drying. It's not the most accurate of meters but it gets the job done.

[George Bokros]

I have that moisture meter also. It will not read a moisture content below 5% per the manual.

[Nick Decker]

I, too, have that meter and feel like it works well for the price. I've never used it on construction lumber, but it's never failed to give me a reading on hardwoods. I always stick it in end grain, preferably after a fresh cut.

Are the batteries fresh? If they're the ones that came with it, try some different ones.

[Lee Schierer]

I've got a Mini Ligno and I can't recommend it highly enough.

I have the Mini Ligno also and it works great.

[Yonak Hawkins]

I always stick it in end grain, preferably after a fresh cut.

It's good that you use it on fresh cut lumber when you measure from the end grain. The end grain dries the fastest and is, likely, not indicative of the rest of the board, especially if the logs have been cut almost any amount of time before the boards are cut. The ends of fresh cut boards will begin to dry significantly even after only an hour or two.

[John K Jordan]

Can anyone recommend a decently priced moisture meter?

Hard to know what a "decent" price is. I do like decent quality tools. I've had a Wagner MMC220 pinless meter for years and it seems to work well on everything. It does need a small flat surface so it's not useful on round things.

[Yonak Hawkins]

John, I have the Wagner MMC205 and, frankly, I just don't know how much I can trust it. There seems to be such a wide variance when choosing by species and, well, within a species (especially ash, I'm finding out) there can be quite a disparity in densities from tree to tree and, even within a tree, top to bottom. Do you know of a way to calibrate the meters or, somehow peg it to a known moisture content ?

[John K Jordan]

John, I have the Wagner MMC205 and, frankly, I just don't know how much I can trust it. There seems to be such a wide variance when choosing by species and, well, within a species (especially ash, I'm finding out) there can be quite a disparity in densities from tree to tree and, even within a tree, top to bottom. Do you know of a way to calibrate the meters or, somehow peg it to a known moisture content ?

Moisture meters are notoriously variable. If wood was homogeneous like plastic things would be different. I have dogwood, for example, that has vastly different densities - some is from different trees and some from different parts of the same tree. The pinless meters need to know the wood density and if it varies the numbers will vary.

I get different readings on the end than I do on the side grain, but I think that depends somewhat on where the wood is in the drying curve. Since the pinless Wagner only measures about 3/4" or so down it works better on boards than thick wood. I use mine mostly on thick turning blanks and have found it is pretty close - for example I'll check all four sides of a block and take an average. When I dry a batch of wood I also dry some 1" thick test pieces and check those as well - if the thick stuff from the same batch shows a higher moisture than the test pieces I know it is probably not yet at equilibrium.

I don't know if there is an internal calibration on the Wagner. If you suspect it's not accurate perhaps the company can test it.

You can calibrate the meter for a specific batch of lumber using a board you can cut some pieces from. For example, cut two piece somewhere away from the ends and edges of the board to get the most even internal moisture gradient, measure both with the meter to make sure they are about the same, seal one in a zip lock bag as a control. Use the oven-dry method to determine the true moisture content of the second piece. Based on that MC, adjust the species number in the meter until testing the control piece gives the proper MC.

This, of course still doesn't help in general if the density of that board is atypical for that species. However, when measuring wood I dry myself along with a 1" test piece I mentioned above AND I know the wood has been drying long enough for the 1" piece to reach equilibrium MC, then using the meter on thicker pieces is accurate. Any density variation of that batch from the typical won't matter as long as the number from the thicker piece is close to that of the test piece. Note that I write the date on each piece of wood I dry so I can estimate the dryness based on time - the dogwood, persimmon, and some other species I'm turning now have been drying indoors for 12 years now so the thinner pieces are certainly at equilibrium MC. (periodic weighing of the test piece can also insure it is at equilibrium)

Where absolute MC is needed the oven-dry method is more accurate than any meter can be.

JKJ

[Ed Aumiller]

I have an older version of that meter... also have a Delhorst pin meter and a Wagner pinless....
All three are normally within 10% of each other.
I only paid $10 for the older version when Lowes was getting the newer version.. It impressed me that
it worked so good...

[Yonak Hawkins]

Thank you, John. This is exactly the advice I need. When you test using two interior board pieces and put one in the oven until it reaches equilibrium MC, what moisture content do you use to set the correct density ?

I don't believe my meter is out of calibration. I was just using that term as to achieve a base point to set accuracy.

[Kevin Jenness]

I have the same distrust of my Wagner meter as you, Yonak, for the same reasons. I have a calibration block from Wagner but still get significant variations within the same batch of lumber that has had time to achieve equilibrium with the shop. I attribute this to the fact that the Wagner is measuring the wood's density and comparing it to an average for the species. I rely on a Delmhorst meter with a slide hammer and up to 1 1/2" pins that allow me to establish the moisture gradient of pieces that are drying. Pin meters do not give a reliable measurement below 5%. I also use periodic weighing of samples to estimate drying progress for kiln operation and blocks too thick for the pin meter.

To establish MC by oven drying, divide the weight of the lost water by the oven dry weight of the sample.

[John K Jordan]

When you test using two interior board pieces and put one in the oven until it reaches equilibrium MC, what moisture content do you use to set the correct density ?


The test I mentioned uses whatever moisture the wood happens to be, preferably not sopping wet but I don't know if that would matter - I'd want it closer to the equilibrium MC since that would be most useful for testing for the shop.
- Cut two adjacent pieces, maybe 3x5" or so, one dry and one as a control. Protect the control piece from losing moisture by sealing it in a plastic bag while you dry the other piece in the oven. Since the two pieces are cut from an adjacent area near the center of a board the one to be dried should initially be at the identical or nearly identical density and MC.
- Dry the the sample in the oven until it has zero moisture.
- Set the density/specific gravity value in the meter to the species as listed in the table that comes with the meter. Measure the MC of the control piece. I would measure from both sides and take the average.
- Compare the value from the meter to the MC calculated from the oven-dried sample. If they are different, adjust the density/SG value on the meter and measure the control piece again until the reading is the same as the calculated value. Now you know the meter is as good as it is going to get and you can test all the boards in the same stack with confidence and have get a pretty good idea of other boards of the same species, remembering the issues with natural wood density variation.

If unfamiliar with the oven-dry MC method you can google something like oven-dry moisture content for wood. This came up, probably as good as any:
https://ir.library.oregonstate.edu/downloads/jm214q048

Note that I never rely on any moisture meter to give me an exact MC. I don't care that much. But I do rely on it to give me a good idea of how far the wood is along in the air drying process. If I dry a 1" test piece along with the thicker wood the numbers can easily give me confidence the wood is dry enough for what I want to use it for. As mentioned, anyone who needs to know the precise MC should probably use the oven dry method. (Only a small piece of wood is needed - the 3x5" size I mentioned is bigger than needed only because the pinless moisture meters need a flat area at least as big as the sensor pad on the back of the meter.) You can read more about the practical determination and use of dried wood from the woodweb or from numerous books. My favorite is "Understanding Wood" by R. Bruce Hoadley, written by a guy who is both a craftsman and a wood scientist.

Please understand that I'm no wood drying and MC expert! I have read a lot and am happy with the results I get from my meter on lumber I cut on my sawmill and turning wood blanks I dry. (I almost always turn dry wood.)

Hey, anyone with a Wagner that is unhappy and wants to part with it send me a note (or post it on classifieds) - I might be willing to take it off you hands for dollars or trade for something. I'd like to have a second one to loan to friends.

JKJ

[Tim M Tuttle]

Thanks for the info everyone. I just cant seem to get a reading on anything other than construction lumber. I'll give the Ligno a try.

[Yonak Hawkins]

Thank you, John. I guess I'm thick-headed. I still don't understand.

..So I have a piece in a plastic bag which maintains the original MC. I have a piece out of the oven which has reached equilibrium MC. Measuring them will naturally display different measurements as long as the original board was not completely dry. If I knew the MC of the "dry" piece, I could use that as a base line to set up the meter for the "wet" piece.

You refer to "calculated value" in your fourth bullet. What are you meaning by that ? How do you calculate the MC of the oven dried sample ? Otherwise, it seems to me you are saying to measure the two pieces and, if they measure differently, adjust the SC value until they measure the same, but the MC of the two pieces is not the same.

[John K Jordan]

Thank you, John. I guess I'm thick-headed. I still don't understand.

..So I have a piece in a plastic bag which maintains the original MC. I have a piece out of the oven which has reached equilibrium MC. Measuring them will naturally display different measurements as long as the original board was not completely dry. If I knew the MC of the "dry" piece, I could use that as a base line to set up the meter for the "wet" piece.
You refer to "calculated value" in your fourth bullet. What are you meaning by that ? How do you calculate the MC of the oven dried sample ? Otherwise, it seems to me you are saying to measure the two pieces and, if they measure differently, adjust the SC value until they measure the same, but the MC of the two pieces is not the same.

No, you never have to measure the dry piece with the moisture meter. You know by definition it's is at 0% MC by way of the oven-drying process. (I haven't tried it by I imagine a pinless meter might give an invalid reading.) The only purpose of drying that sample piece is to calculate the MC in the "wet" board. Once you use the dry piece to calculate the MC by the formula then you know what the MC is in the "wet" piece and can fine tune the meter for that species.

You calculate the MC in the board after drying the sample by weighing it before and after the drying and using the formula

MC - (InitialWeight - OvenDryWeight) * 100% / OvenDryWeight

For a good explanation you can google something like oven-dry moisture content for wood. This PDF came up first, probably as good as any:
https://ir.library.oregonstate.edu/downloads/jm214q048

Besides the oven, you do need a good scale. The smaller the sample size the more precision you need in the scale but small scales are cheap, even those that can weigh in 1/100s of a gram. I have a laboratory triple-beam balance scale (which is overkill) and keep these in my shop for various weighing. The first two are tiny, excellent for small things. The third one is a general purpose scale but the 1g resolution would not be as useful for small wood samples but you can use a larger sample.
https://www.amazon.com/gp/product/B0012LOQUQ
https://www.amazon.com/gp/product/B002SC3LLS
https://www.amazon.com/gp/product/B002UEZ2FC
I've tested these with a set of precision calibrated weights and they are all very close. For oven-dry MC tests you really only need the relative weight, not the absolute, so as long as a scale has sufficient resolution and is reasonably linear over the range it will work fine.

(OK, I admit I may be a scale and test instrument nut. I have other digital scales and two good to 600 lbs I use to weigh llamas and mini-donkeys.:) )

Hey, an easier method: drive up this way with your meter for a visit - we can oven-dry and weigh wood, compare meters, and play in the shop! I have plenty of air-dried boards willing to sacrifice themselves for science. :)

JKJ

[Yonak Hawkins]

John, thank you for your help and for your time to write all your notes and links. Now it's up to me. I'll have to put on my lab coat, muss up what little hair I have, install the pocket protector and get to work. If you need me I'll be in the lab. Thank's so much.