Is my moisture meter working?


I just bought a "MD-26 Timber Moisture Meter".
All the wood in my basement, be it stored hardwood or construction 2x4s, measures 6% moisture. The wood in my 1st and 2nd story (completed projects) do not register; presumably below 6%.
I bought the meter because I just cut and stickered a 4' high pile of walnut, also in my basement. The wood at the bottom measures 24% and the wood near the top of the pile measures 14%.
The meter is consistant; it will give the same reading over and over again; but I am sure if it makes sense. May in Rochester NY is not all that arid; my wood should not be below 6%. And my freshly cut wood should not have gone from 24% to 14% in one week.
Do I have a defective meter, or do I not understand something? Thanks.
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I'm east of you and would expect readings of 12% in a dry basement for wood that has been stickered and stored for awhile. Tried finding that model of moisture meter and cam up with zip. Is it a pin or pin-less model and have you tried a fresh battery?
Bob S.

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http://www.rockler.com/product.cfm?page 447
It came with a battery. I could try another... What would you expect 1 week old wood to measure?
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Toller,
I get kiln-dried wood from Lakeshore Lumber near Pulaski and I check it with my meter at the time I pick it out. They guarantee 8% or less - or it's free (never had a chance to take him up on that either). When I sticker it in my walk-in basement (insulated and has a dehumidifier), the wood will slowly creep up to about 10-12% in several weeks. That's pretty consistent across all kinds of hardwood I've purchased from them over the years.
Something does not sound right with your readings, so try this. Take two pieces of wood, one that is at 6% or less and one that is much higher that you can drive some nails into. Take two #8 finishing nails (shiny ones - not coated) and drive them into the edge of the boards - not close to the ends. The distance between the two nails should be the distance between the pins on your meter so they will read the same. Drive the nails in about 1".
Take a measurement as you normally would, on the edge, pushing the pins of the meter into the wood by hand and record the reading. Now take a reading off the two nails - any difference?
If it's significant, one thing that may be causing the low readings is case hardening. The wood was dried to fast and the outer layer is a lot drier than the inside. Another cause of different readings is pushing the pins into the end grain one time then into the edge of the wood the next reading - lots of variance depending on how the wood was dried.
On construction lumber - like your 2x4, it comes from the mill at about 20% mc and will take a good 3 months to get down to 12% in this area at this time of the year. Try drying it faster in the basement by using a fan blowing on it usually results in a lot of 2x4's that can be used for making arched window frames. Need any arched 2x4's.......
Try a new battery and maybe even another meter if you can borrow one and if the readings are still at 6% and the wood is dried properly and not case hardened, then you found a good source. It will eventually come up to equilibrium for this area which is 10-12% for wood stored in a dry basement.
Also keep in mind that this class of moisture meter is not going to be extremely accurate and it's a "relative indicator", not an exact measuring device.
Bob S.
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Follow-up.
Also consider that the readings you're getting from completed projects were (most likely) in a nice heated environment all winter and dry as hell - now. Wait a couple of weeks (rain forecasted all next week for this area) for your house humidity to get up to normal (RH 40% +) and measure again.
Bob S.
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There's the answer, only poorly enunciated. Check the relative humidity in the area where the wood is stored, then check against the table EMC for that relative humidity.
A "dry basement" can mean a lot of things. Mine's the 4' deep kind and is heated, so the lumber stored there is at 4% right now - but climbing. Dehumidifier will go on line by the beginning of June, but to maintain 55% in the shop it won't run much save when the rains come.
You didn't mention the corrections for your meter. Most have to have them to be even close to accurate across species.
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It is a standard 8' heated basement. Your wood measures 4% now? Where are you located.

No, it doesn't have any corrections; probably too cheap.
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I'm where it snowed yesterday, and the wood-burning furnace was required all day. Probably should light it now, but it's 66 inside, and only a few below downstairs. Just came up from there, and I am wearing short pants.
Get a humidity gage and use it to "calibrate" your meter. With pretty constant humidity for a couple of weeks and the tables from fpl, you can work up your own species corrections.
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That might work, but what is fpl?
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George,
Care to expand on that? How will having a humidity gauge help him "calibrate" his moisture meter. The moisture meter is essentially a megohm meter that is based on resistive readings, not on ambient or relative humidity. I may not have enumerated my response very well but yours doesn't make a lot of sense for calibrating a moisture meter.
Here's but one reference
http://www.ffp.csiro.au/mm/Resistance/Meter%20Calibration.htm
Click on the links on the side to go to individual sections for the "How To" and "Why".
I'm sure there are many other references that are more up to date but this one addresses just about everything discussed in this thread. After reading this, I learned that your meter is most accurate in the first 2 to 3 seconds and then the reading starts to vary with time. My suggestion of driving in two nails cane from another site that showed how to make your own kiln and how to monitor the mc of the wood being dried.
I believe Steve Knight made the drier and made a number of posts on this subject and how he measured how dry the wood was by using both a weighing method and resistive readings.
Bob S.
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Made one with an old Telco "megger" years ago, calibrated it against the meters at the college.
Think about it. With constant or nearly constant humidity, he should read the EMC for that RH. Differences between species would be "corrections" to the meter.
fpl = Forest Products Laboratory http://www.fpl.fs.fed.us /
A resource URL that should be bookmarked on every woodworker's computer. The tables in the Wood Handbook are the source for EMC-MC comparisons.
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George,
Ahhhhh, you didn't say you had an outside calibrated reference (meter at the college)..... that's cheating.....;-)
But even so, I don't think that is an accurate method since the various species of wood need to be at equilibrium (known reference point) which he would need a calibrated meter to read their mc to start with - which he doesn't have (for sake of our discussion). But... he could do the old standby of measuring their weight, then drying them slowly in an oven until there is no more change in their weight. That requires an accurate weighing device which I'll assume he also doesn't have (unless he's gone postal on us...).
As for your "megger", you calibrated it against another meter that was most likely calibrated to a standard. So without using another known reference (calibration source) or drying the wood down and then see what the weight difference is after they reach EMC - he has no reference point to calibrate against that I can see but maybe I'm not thinking this through all the way either.
In reality, the difference between the typical species most of us use is negligible and applying the correction factor (according to my meter's table) it may at best be +/- 2% at most. Critical if you're the one doing the drying in a kiln but you wouldn't be using a $39 meter most likely either. So while we've told him about his problem, we haven't exactly given him an answer he can use, so I propose the following solution:
1. He measures a sample of wood and records his readings. 2. He then wraps the piece in Saran wrap so it is in an air tight packaging and ships it to me. 3. I'll use my meter, adjust the reading for the species, re-wrap it and ship it to you. 4. You then take your megger, calibrate it using the RH and any tables you have and take a reading. 5. We then all post our readings here and he can take the average reading and use that...
-or-
He could just say - the meter indicates that it's below 10% - close enough, use it .............;-)
Bob S.
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Actually that is kinda what PSI said. I emailed them and they called me. He said that if it showed 6% on wood in my basement and top of the scale on my arm it was doing pretty good. I think the "solution" is to compare new wood to wood that I have had a while. If they read the same, the new wood is okay. If the new wood reads higher, it has to dry more. Might be all I can expect out of a $29.95 meter (it was on sale)
Appreciate your help though.
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You're welcome. I paid 3 times what you did and I doubt mine is any more accurate than yours. I have now way to calibrate it against a known standard.......unless........we both send our meters to George, then he can sneak into the college some night and test our meters against theirs.......;-)
Bob S.
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Nope, I could just as readily calibrated against the tables of EMC vs RH that I referred to. The cheeseheads have done all kinds of tests to arrive at the data, might as well take advantage of it. We stored at 45% RH at the college (~20C/68F), giving us an 8.4%. If the meter read 8.8 at the surface, it was in error or we checked the arrival date.

Not sure you understand that RH / EMC concept. If species A says 6% and species B 8% in the same controlled environment which should give 7% EMC, then you have a provisional correction of +1 and -1, respectively. Now follow changes and increase your sample size.
As to oven drying, the advantage to NDT is the number of samples you can take. Overall, I think this is going to be more meaningful.

Or, as I, who no longer bothers to meter, say - It's not as if drying it for use next week will make a difference week after next.
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George,
You're absolutely right. I use the moisture meter I bought a few years back after I got stuck with some badly dried white oak from a now defunct supplier. I've compared readings with two other meters better rated than mine and its close enough. It is good to have a meter though so you can better judge the wood when someone say's "this wood has been air-dried in the barn for x years" and it still reads 18%......
Bob S.
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with
Hey Bob - next trip up, give me a call. We'll hook up and go up together. I'm in the phone book in case you lost my number. First stop - Dunkin' Donuts - now open in Parish.
--

-Mike-
snipped-for-privacy@alltel.net
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Ok....
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My moisture meter has a setting for different species of wood. Oak for example, and mahogany have different characteristics that have to be considered in calculating moisture content. Maybe you're not setting these correctly.

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