Thread: Crommelin moisture meter

Originally Posted by Dengue

Has anyone had any experience with the Crommelin Moisture Meter? It is avaialble from the big green brick shop.
is there any way of checking the accuracy of these meters?

Yes but you will need a set of scales that can measure to about 1g
Take a length of wood and cut it up into pieces (not too small or too large - that you can weigh) - something like 150 mm long pieces of 100 x 50 mm is OK.
Discard the end pieces and measure their moisture content with the meter in the middle of the cut sides and average and record these readings for each piece.
You can also measure the MCs with teh meter on teh non cut sides for comparative purposes.
Then weigh them individually with the scales (record and call these weights WS).

Heat in a 100+ºC oven - (110ºC is plenty) - too hot and you will lose more than moisture.
Periodically weigh the pieces until they no longer change weight (record these and call them W0)

Absolute moisture content (AMC) for any one piece = 100 x (WS-W0)/W0

Average all the individual AMCs for the MC of the original piece.
Don't be surprised if you are a long way out.

Maybe you didn't want to hear of the amount of work needed?

Don't be surprised if you are a long way out.

thanks BobL. Interesting experiment. Can you recommend any reasonably priced Moisture Meter that is reasonably accurate?

Joe at $45 I'd have to doubt its accuracy. I keep reading that with moisture meters you get what you pay for. If you do get one be aware that if there is any moisture on the surface it will confuse a cheap meter. Apparently Wagner meters aren't fooled by surface moisture, but they are 10 times the price or more......

Originally Posted by Dengue

thanks BobL. Interesting experiment. Can you recommend any reasonably priced Moisture Meter that is reasonably accurate?

All commercially available meters need to be calibrated in the way I suggest for aussie timbers.
Some have the ability enter the wood density which applies a half reasonable correction.
Correction tables are available for some Ausiie timbers for some meters but you have to pay for these.

Moisture meters are like air flow meters and particle counters - you can't just poke the meter at the wood and get an accurate answer.
Contact meters really require the wood be cut open to reveal an internal surface and you can't just rely on one measurement but you need to measure several - most DIYers don't have that much wood to waste to do this

As FF says you can pay the big $$ and get something like a Wegner.

In most cases absolute accuracy is not needed - you just need to know things like.
Is this piece approximately drier or wetter that this one.
About how much has the moisture changed since yesterday or last week.

I got the impression that you only needed the specific gravity of the timber to make each adjustment. (now whether they mean the SG of green or dry or as it is when measured I don't know). In other words you may even have to make adjustments between different boards of the same species if the boards are different weights for the same volume. Have a look at Mattias Wandel using a Wagner.

Those pin type meters just measure the conductivity of the material you jab the pins into. Moisture and other impurities will conduct electricity. Increasing the surface area of the contacts will also alter the reading. That is why expensive moisture meters have a hammer gadget to drive the sensing pins into the timber. To get an accurate estimation of the moisture level of a timber species you need to "calibrate" the meter. Grab a lump of whatever timber you commonly use in it's natural moist state, take a reading and record it, then dry the timber using the methods outlined above and then take another measurement and record it. You now have 2 reference points for a particular species that you commonly use. Repeat the process for other timbers that you use.
Or spend a lot more than $45.00 for a meter that is calibrated for Australian timbers. Or spend less than $20.00 at somewhere like Jaycar and buy a simple digital multi-meter which will do the same thing as the thing from the big green shed but which you can use later for finding faults in wiring and stuff like that, long after you get sick of consulting calibration tables that may, or may not, be all that accurate anyway.
And yes, I did buy a Cromelins meter as an experiment. No two bits of firewood from the same tree cut at the same time register the same moisture content.

Originally Posted by Old Hilly

No two bits of firewood from the same tree cut at the same time register the same moisture content.

That' not uncommon but it's probably not because of the meter. Thats' why you have to take many measurements and do some stats.

Probably not Bob but it's still a problem, especially if you follow the new guidelines that come with some new wood-burning heaters. Sorting through a wood heap would get pretty ordinary very quickly. I would think that the problem would also occur if you were checking the end-grain if a stack of timber. Perhaps one has to measure the moisture levels somewhere towards the middle of the stack? Or measure the ends and then the center and average out the result? Or is the Wagner machine the only way to go?

Well if $512 is within your range then I would say get a Wagner (that's the local price, in Melb). Multiple readings in literally a few seconds.

Originally Posted by Old Hilly

Probably not Bob but it's still a problem, especially if you follow the new guidelines that come with some new wood-burning heaters. Sorting through a wood heap would get pretty ordinary very quickly. I would think that the problem would also occur if you were checking the end-grain if a stack of timber. Perhaps one has to measure the moisture levels somewhere towards the middle of the stack? Or measure the ends and then the center and average out the result? Or is the Wagner machine the only way to go?

The Wegner type meter avoids the need to cut and measuring the MC inside a piece of wood which is needed for accurate MC measurements using contact type meters.
But even using a Wegner to assess the MC of an unseparated stack will require the stack to be taken apart and the MC has to be measured of timber in the middle of the stack.
Stacks separated by wooden strips (stickers) are more likely to be more uniform.