I rough cut an 18″ wide 4/4 sapele board, in order for the pieces to acclimate for a couple of weeks. I measured the initial moisture and wrote it on a small piece of tape on each piece, stickered them and placed a fan nearby to move some air. In 3 days there has been no movement in moisture, according to the Wagner pinless meter.
My issue is that my Wagner meter shows 12%, while the PSI pin meter shows less than 6%. Assuming that the pinless Wagner measuring 12% is measuring near-surface moisture, why is it not moving? The RH in the shop is 42%, so surface moisture should be moving a little.
The question is which is correct, if either? Any thoughts? Wish I could dry a sample in the oven, but that ain’t gonna happen!
Replies
Where are you? Lumber never reaches 6 percent in my neck of the woods.
Try weighing a board and check to see if it loses weight after a few days or a week. That will also tell you which moisture meter works. Let us know.
If a meter is saying 12% and the other 6%, one of them or both are wrong. The pinless meter does measure deep, I recall the instructions saying 1 1/4 inches deep and it requires a conversion table according to the density of the wood being measured. I dont think 3 days in the shop will change the moisture content of wood beyond the accuracy range of the meter .
I have a pinless Wagner meter that allows the user to enter a conversion factor based on the lumber specie. When you use the meter is there anything under the board you are testing. When I test a board that is less than about 1 and 1/2 inches thick and that board is resting on another object the meter reading is effected by the object underneath.
The percentage moisture is the weight of water as a proportion of the total weight of the wood. It is very different from relative humidity which is the amount of moisture the air contains compared with its maximum possible loading. 42% is quite dry so if it is warm, you would indeed be expecting the wood to dry out some, if it is going to do so. Have you tried the pin meter on the freshly cut ends?
I don't use a meter (skinflint) but have the advantage of my favourite wood yard being open to the same environment as my shop - it's 2Km away and identical climate as a result, and both are open to the air. Nevertheless, I do try to buy wood 3 months in advance of a project and just leave it in my shop until ready to use. If your wood has been in your shop for a few weeks then I'd call it good.
OK - both meters were wrong.
I cut a small piece of the sapele and measured it carefully with both meters. The PSI pin meter showed less than 6%, measured both on the face of the board and the freshly cut end grain. The pinless Wagner meter showed 12%, corrected for specie.
The piece I used for the test was a 1" strip across the board. I used the short dimension in order for the moisture to escape faster through the end grain.
I first weighed it to the nearest 0.001g. Then it went into the microwave for periods of 1 minute for the first 6 heatings, weighing after each heating cycle. The it "rested" for 30 minutes. Then changed to 2 minutes in the oven.
After 8 heatings, the weight seemed to have stabilized. I let it sit overnight to equilbrate. Then reweighed and repeated the heating for 4 more cycles. It gained a little weight overnight in the shop at 42% RH.
Once I got 3 consecutive weighings with no measureable change I declared it to be dry (end of experiment as the microwave died). At this point, the scale actually registered it gaining moisture from the air.
Bottom line 8.9% moisture. So both meters were wrong. Now, what can I trust?
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