Moisture Meter readings

[Apprentice_GM]

G'day All,

I received my moisture meter today, which I intend to use a lot in my upcoming Holz Hausen experiment, but as you do I ran around testing various pieces of wood and have some questions.

I tested a piece of building pine scrap I had laying around, an off cut of a 3" x 1 1/2", and it registered 10%. I would have thought this was a little high, I expected such timber to be so dry it would be less than 5% moisture. Thoughts?

I then tested a cheap pine coffee table which was stained and it came back 10% as well. That coffee table is well over 15 years old and was made with building timber which from the above test one would assume was 10% when it was built. Is 10% as much as pine will dry out, or does the stain keep the relatively low moisture content from drying out?

I tested a piece of ironbark I had, this is an ex-railway sleeper, very hard and dense (~50% harder and denser than hickory) and it came back 19%. Now that piece has been sitting on top of blue metal stone in the sun, wind and bugger-all rain for 25+ years before spending the last 3 years at my place, on my porch under cover but where the sun hits it in winter, 19% seems way too high. I was only testing the end . . . perhaps the atmospheric humidity affects the result? Perhaps if I cut into the middle of that piece it would be ~5% as I expect?

Does anyone have a good suggestion for constantly testing the middle of a piece of wood? I presume some way of drilling a section out large anough for my meter prongs to fit into, then sealing it well enough so the surface of that section doesn't dry out and give you a falsely low reading?

 

[Shipper50]

I also have been taking readings with my double pin moisture meter I got off ebay. I have a cord or so of split hickory that I have been splitting and stacking in the sun this past month. I put my wood on pallets and took some readings of the first stack when I got it. It read 37% and now it reads around 28.

I then took my meter and checked a piece of fired wood that has been in my basement since April and it read 16%. I then took the meter and stuck in my basement stair tread and it read 16% and its been there at least 10 years. I take my readings from the end of the wood and push in the pins are far as I can. I don't drill any holes and have found if I take a reading from the middle of the split it doesn't really read that much different with my meter.

Shipper

 

[Adios Pantalones]

The moisture content of wood is directly correlated to the atmospheric %relative humidity. At 30% RH, wood will equilibrate at 6-7% MC. I think that it takes something like 50%RH to produce 10%mc wood. So- whether it's kiln dried, oven dried, or aged at the bottom of a lake for 10 years- the current %mc will depend on the %RH that it's experienced over the past year or so.

Wood outside that gets rained on won't normally go below maybe 15-20%- depending on heat and humidity of course. I don't know if drying upside down has an effect for you people on the wrong side of the planet.

 

[BJ64]

G'day All,

I received my moisture meter today, which I intend to use a lot in my upcoming Holz Hausen experiment, but as you do I ran around testing various pieces of wood and have some questions.

I tested a piece of building pine scrap I had laying around, an off cut of a 3" x 1 1/2", and it registered 10%. I would have thought this was a little high, I expected such timber to be so dry it would be less than 5% moisture. Thoughts?

I tested a treated pine board under my deck and got 27%. I have the same reaction as sawdustburners. I figured that piece would have been dry, dry dry.

 

[Jake]

at work, I use a delmhorst j2000 which I'm able to change specie and temp.

KD wood in our area is usually 6-8%

 

[pybyr]

I am intrigued by the idea of a moisture meter to evaluate the readiness-to-use of firewood, but here's what I am puzzled by--

how can the low cost meters actually give anything resembling an accurate reading-- for the following reasons:

they all seem to work with two pins, and I assume must measure the amount of electrical current that can flow between those pins

water (moisture) by itself conducts relatively little electricity, until you add other elements or molecules which help create ions, and what else you add to the water, and in what concentration, can make huge differences in the conductivity of the water/ moisture itself

various species of wood, and/ or wood grown under different conditions, must have widely varying amounts and types of chemical ions in addition to water molecules.

I can believe that a cheapie two pin meter can indeed measure the relative gain or drop of a sample piece of wood as that same piece of wood gains or loses moisture-- but how can the cheapie meter really manage (or plausibly pretend) to measure absolute moisture content across wood species and other variables?

 

[Apprentice_GM]

Yeah I'm with you - I wonder how accurate they are. I would have thought you'd need to enter species type or some info before it could calculate moisture content based on resistance (I concur with you it probably puts a 9V charge across the pins (my battery is 9V) and measures current) as surely resistance would change with factors other than moisture content eg density of wood?

The previous poster mentioned his moisture meter did species, I bet he means he enters species info to get a more accurate calc of moisture content, his meter probably has tables of wood types, and resistance at various moisture content levels. Just a guess.

 

[BJ64]

Good points on conductivity vs. various species. I think I would benefit from the cheap meter as a way of monitering the drying progress on my own wood. When I cut it and measure I can see that the meter is pegged out. When I am ready to burn the wood I can see how the meter reads when on wood that burns well vs. wood that does not burn so well. Wether the meter is accurate or not I should be able to use the instrument to decide with come consistantcy which wood is better to use and which better to let sit longer.

There will be times when I may have to send the kids out to get wood from the various piles I have on the place. Some may still be too green and with kids being kids they may not have the judgement to make that call. With the meter I can send them out with instructions not to bring any that average over some "percentage" of moisture.

 

[pybyr]

I tested a treated pine board under my deck and got 27%. I have the same reaction as sawdustburners. I figured that piece would have been dry, dry dry.

the chemicals in pressure treated wood often include copper or other metal compounds, any of which will very likely raise the electrical conductivity of wood- separate from moisture- above untreated wood. that, rather than moisture, may explain your reading; of course (I hope) no one is burning treated wood, anyway

 

[BJ64]

I tested a treated pine board under my deck and got 27%. I have the same reaction as sawdustburners. I figured that piece would have been dry, dry dry.

the chemicals in pressure treated wood often include copper or other metal compounds, any of which will very likely raise the electrical conductivity of wood- separate from moisture- above untreated wood. that, rather than moisture, may explain your reading; of course (I hope) no one is burning treated wood, anyway

You are right. That was a treated 2x8 and since it is sorta green in color I suspect that it was treated with a copper based material.

That would make some sense.