Wood Moisture Measurement Delima

[Mike Goetzke]

I have an Electrophysics moisture meter that I bought second hand years ago. I'm a hobbyist so don't use the meter often and have a question or two. I bought some rough sawn wood from a supplier that I have used successfully before. I bought some 4/4 and 6/4 Kentucky Coffeetree for a project that was supposed to be kiln dried. It has sat in my garage for a few week and first off I noticed two of the five 8' x 7" pieces of 6/4 are showing bow - one about 3/8" in the middle. I planed the surface of three boards and decide to take out the moisture meter to make a check. The meter can make pin & pinless measurements. I measure from 55 to 80% moisture in the pinless and 11-12% in the pin modes. I have a piece of walnut and a piece of beech - the pinless and pin readings are about the same 9-10%. Any ideas what is going on before I contact the supplier?

(I'm building an 80" long tabletop from the 6/4 and want it flat!)


Thanks,

Mike

[Jim Andrew]

Is the electrophysics meter a low cost meter? I bought a cheap meter, and found it to not be accurate. There seems to be a direct correlation between cost and accuracy of moisture meters.

[Mike Goetzke]

Is the electrophysics meter a low cost meter? I bought a cheap meter, and found it to not be accurate. There seems to be a direct correlation between cost and accuracy of moisture meters.

Actually this meter new is $325. I did contact the sawyer and he had the same problem measuring MC of the wood in the pinless mode with his Wagner meter. While drying he just used the pin mode. I'm happier right now.

Thanks,

Mike

[Scott T Smith]

Pin type meters measure the resistance between the pins. Thus, they are suitable for measuring at the surface of the lumber (which is usually drier than the core). If you want accurate readings from the core of the lumber with a pinless meter, it is best to use insulated pins.

Pinless meters read at a specific depth - typically around 3/8" for an inexpensive meter. Other pinless meters are designed for reading veneer (shallow depth of reading), or 1-1/2" deep for kiln operators.

Your pinless setting is probably reading the MC% of the core of the lumber, and the pins are providing you with a reading on the surface.

One other item to consider is that different species of wood have different resistance values, and that these measurements are also affected by temperature. Higher quality meters will allow you to enter in a code for the species of the lumber, as well as the temperature at time of measurement, so that you obtain the most accurate reading.

[John TenEyck]

I would cut 6" off the end of a board, and then cut off another small chunk. Weigh that chunk then put it in your oven at around 200 deg. Weigh it every hour or two until it stops losing weight. Then calculate the MC = (wet weight - dry weight)/dry weight x 100. That MC is the average of the wood. The results will help tell you whether your moisture meter was giving bogus results with the pinless setting or if it was telling you that the inside was really wet.

John

[Alan Lilly]

The electrophysics meter is good quality, but you have to lightly plane a spot of the wood smooth for the meter and look up the wood species on the wood density chart. The reading is dramatically different depending on wood density. So you have to use the chart to compensate the measurement to the appropriate moisture reading.

[Mike Goetzke]

I would cut 6" off the end of a board, and then cut off another small chunk. Weigh that chunk then put it in your oven at around 200 deg. Weigh it every hour or two until it stops losing weight. Then calculate the MC = (wet weight - dry weight)/dry weight x 100. That MC is the average of the wood. The results will help tell you whether your moisture meter was giving bogus results with the pinless setting or if it was telling you that the inside was really wet.

John

My wife was baking so I tried this. The MC came out to about 20% (the meter read 74% pinless when set for 75/dense wood and 12% for the pins when set at 15). This meter has been very trusty with all other wood I have used don't know why this species is giving me issues.

Mike

[John TenEyck]

My wife was baking so I tried this. The MC came out to about 20% (the meter read 74% pinless when set for 75/dense wood and 12% for the pins when set at 15). This meter has been very trusty with all other wood I have used don't know why this species is giving me issues.

Mike

If your data is correct, and no reason to suspect it isn't, then your wood was not KD except maybe to framing lumber standards. 20% is not even well air dried for most areas. I'd be paying a visit to that supplier with your data and ask for a rebate, or return it for a complete refund.

Curious, what does your MM read in pin mode when you measure near the faces and center of a fresh cut board?

John

[Kent A Bathurst]

My wife was baking so I tried this.

Stop right there. While your wife is using the oven for baking, she lets you toss a chunk of wood in there?

You're a braver man than me. Kudos.

[Ole Anderson]

I have a cheap General moisture meter, pin type. I got a load of firewood that was supposedly seasoned but wouldn't burn well. Surface moisture was well under 20%. OK, good. I split a piece and checked the interior moisture, it was more like 30%, well over the 20% recommended for firewood. Moral of the story: Surface moisture does not always mirror interior moisture.

[Peter Quinn]

I'd make an end cut and measure with the pin meter using any necessary temperature and species correction. Most of them are set to measure Doug Fir at 70 degrees........which is great if your are checking framing lumber on a lovely spring day. My Delmhorst has a hammer pin reader that you can pound in to get a core reading, Ive used that at work, but in the home shop I don't have the hammer attachment, so I chop an end off and take a core versus surface reading. If they vary by much or if one is very high I wait. In your case I'm guessing Scott nailed it, pins are measuring the surface, pin less the core, the stuff is wet at core, and you are in for a headache. I'd chop an end and do all your measuring with pins, if its wet at the core.....send it back. Coffee bean is every hard/dense no? Dense=slow drying, my guess is the sawyer didn't give this one enough time.

[Mike Goetzke]

Thanks to all for the comments. I tried working the wood a little more but had more issues with movement after milling. I also made more pin type MC measurements and they reflected that the wood was not dry (9 to 20% at the center of cut board). I contacted the seller and he took full responsibility and is to send a full refund. I'm out maybe 12 hours labor but glad the supplier stood behind his product. He selected this Kentucky coffee tree saying he found it was supposed to be a good outside lumber. This was the first time he worked with it. Now looking for an alternate species for this project. Guess I can just go to the big box for cedar but most seem to use this wood for grill carts and I was looking for something different.

Mike