I'm reading the reviews on Amazon of one such device and a couple of reviewers complain that if they dip the probes into actual water, the meter only reads 35% rather than 100%. Is this a reasonable observation to make?
No. usable MC for wood is in the 10-20% range so being able to indicate much higher than this is useless.
I only use a cheap meter as a comparator. Wood that has been in my workshop for years can be compared to new stock and judged as to whether it is ready to use or not.
It's nonsense. Why it's nonsense is complicated.
Rather than a moisture meter, read your copy of Hoadley's "Understanding Wood" and get a cheap air hygrometer and some patience. Learn the key points of the EMC chart.
A useful moisture meter doesn't have probes and costs >$100. Probe meters aren't as good as an air hygrometer, patience and understanding EMC.
They work just fine providing you don't try and use the probes to penetrate the wood, they just aren't strong enough. Ideally you should cut a section from the centre of a plank, split that in two with the grain and take a reading from one of the split edges. IME it is often very different from one taken near the surface, and it's the internal moisture content you need to know.
It does rather depend on the water doesn't it !! But it also does indicate the knowledge base of those reviewers.
Like Bob, I do wood turning and the moisture level of wood that has been gathered in the raw is important. And like Bob I have a cheap meter (Ebay sourced) that despite its total lack of sophistication is surprisingly accurate. I had access last winter to two trees that had fallen in a gale and it measured a bit over 30% for both which the good books tells me is correct. I then part turned some of the wood and microwave dried it, and the weight loss and moisture content readings kept pace with one an another.
In the professional world where moisture content of many things is critical then expensive and reliable equipment is necessary but for the rest of us the average Hong Kong sourced meter at a tenner seems perfectly adequate, even if only noting the change in value.
Rob
Surely the moisture would be in equilibrium throughout the timber, so why would a measurement at the edge be different than at the centre. If it was wouldn't that be a sign that the wood was in the process of drying out?
Hmmm, I'm only likely to be using it for woodburner logs, so I don't need much more than a go/nogo indicator. Sounds like provided the thing is not DOA, a cheapie will do. Thanks.
It's a very common, natural and reasonable assumption that, in a fully seasoned piece of timber, the moisture content would be the same all over but it just isn't so.
I often receive cracked violins or guitars in the workshop and, if the crack has been left too long (which might be weeks or months or only days) the wood will have shrunk away from the crack making closing it again very difficult and in extreme cases necessitating a splint of new wood to fill the gap.
I had a Victorian Double Bass in my workshop last year. It had a split along the belly that had shrunk away from the crack and opened out nearly 1/8" on a piece of wood only about 3/16" thick at that point. One might have thought that instrument would have had enough time to equalise throughout!
Nick
The probe-type meters are measuring the conductivity of the material, which is going to depend on the type of material as well as the water content. (Hence different scales for wood and plaster, on some meters at least).
If the people who dipped the probes in water (an insulator if it's totally pure distilled water) had tried again with salt water, they would have got a much higher 'moisture' reading.
In the trade, moisture content is only ever a rough average across, say, a lorry load of timber
They measure the resistance of the electrolyte, which is the dissolved salts in the remaining sap, and compare that with a look up table. Pure water is not an electrolyte.
I see people using these meters to demonstrate the "dryness" of firewood yet they are only measuring the comparatively dry face until the whole log is in equilibrium. I dry samples in the microwave, carefully.
AJH
The received wisdom is that you should split the wood to reveal an unexposed surface, which should be representative of the actual MC.
The cheap meters are good enough for the job of giving an indication of the MC of split firewood, My cheap ebay one tells me that the lump of sopping wet "seasoned" firewood is actually sopping wet by saying HH on the scale. (40% is the highest reading).
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