Moisture Testing Variability

      A discussion of factors that could account for a discrepancy between a supplier's wood moisture content readings and the customer's. October 12, 2008

Question
I have a new supplier of wood and when I check the moisture of the hard maple with my moisture meter, it says 15%. I believe I want to be around 10%. The supplier says they check the moisture content prior to shipping and that my moisture meter doesn't work accurately. I measure the moisture content of other wood in my shop and it is around 10%. Is the guy full of bolgona? Should I find a new supplier? He mentioned an oven test. Which is more accurate?

Forum Responses
(Architectural Woodworking Forum)
From contributor G:
Ask to use his meter at your shop prior to unloading.



From contributor C:
Search WOODWEB for "microwave moisture content" and you'll find a simple technique to get a precise measurement of your stock. Be sure to pay attention to the part that says to turn the microwave down to about 30% of its power setting. You'll also need a scale, but a kitchen scale can be okay.


From contributor V:
I have had the same thing happen. I used a pinless meter that I paid 300 for. I found that they were using pin meters and checking the sides... Make them cut a board and check the fresh end. Then check a board that you provide that you show to be 10%.

I had a guy like your supplier one time. He was a custom miller and dryer. Went down to pick up a load of wood and check it with my meter, and low and behold it was over 45% but it was 10% with his meter. I grabbed a piece of wood I knew would be dry, checked it and had him check it, showed him it was not my meter. Then made him cut one of his boards and stick his little pin meter in the cut end, and low and behold, it was wet.

Guy told me don't worry, I'll put it in the kiln and have it dry for you in a week. I thought yeah right, if that's dry in a week, it will not be worth buying. He called back about a month later and said it was ready. I went back down and checked it and it was 25-35%, so you can guess the rest of the story.



From contributor N:
As a sawyer soon to be dryer operator, I'd be thinking maybe 1400 could get me the "right" meter. Oven tests done correctly cannot to my knowledge be argued. If the kiln operator does not provide proper MCs, they obviously are not interested in repeat customers. Not one of my customers has failed to return. A small market with a small operator pretty much demands that I provide a quality product.


From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
On fairly dry wood, I tested three moisture meters (Delmhorst, Lignomat and Wagner, the last one being pinless). As a quick summary, they were almost always within 1% MC of the true value.

As a general rule, spend about $200 for a meter; anything less is probably not a good investment. The first thing is to use a standard MC meter and not one made outside of the USA. Check the batteries. Then follow the instructions in the link below.

Inside a heated shop (heated 24/7), you will find about 6% MC in the wintertime. A value of 10% MC is 50% RH, which is quite high for the wintertime; 30% RH is 6% MC. Delmhorst Instrument Company used to sell a resistor that you could put across the pins of a meter to check the meter's accuracy. Wagner makes a plate to check their pinless meters.

I would guess that it is more likely that your meter readings are incorrect. Meters that are not working tend to read higher than normal.

How to use a moisture meter



From the original questioner:
My meter is a Wagner pinless type. It is only a couple of years old and rarely used, if this helps.


From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
Proper use of this meter requires an adjustment for the density of the species. Perhaps this is where the error is coming from. When you check a piece of 4/4, do you have air underneath? Check the link given to make sure you are following the other suggestions. Note that if the surface has recently regained moisture, you will get a high reading, even though the average MC is lower.


From the original questioner:
No, I did not have air underneath. But I tested the old maple I had in the shop and it was around 8-10% and then I tested the newly delivered after it had sat in my shop a couple of days. The new maple was coming in with a moisture level of 15%.


From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
If it came on a truck in the morning when the RH was high, the high surface MC will give you a high reading.


From contributor V:
I used the Delmhorst pinless. Cost was about 300 four years ago. As I pointed out, cutting the wood revealed a wet center, and I mean so wet you could see how wet it was. That is why I recommended testing a piece of known wood with the meter.

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