moisture content

[Gecko]

Lets see if I have this right. I took a piece of Holly I have and jointed it, planned it the ripped a 12"x1"x3/4" piece out of the middle. I weighed it (102 grams) then popped it into the oven at 170 degrees. I kept taking it out and weighing it until it stopped losing weight (90grams) I then used the formula (initial weight minus final weight divided by final weight; multiplied by 100 will equal %MC). This gave me 102-90=12, 12/90=0.1334, 0.1334x100=13.34%MC.
Is this correct? And at what MC is this wood usable?
Thanks for any input as I am totally new to this wood drying/moisture content thing. :)

[TDHofstetter]

I don't think that formula's right - it'd depend upon the initial moisture content, which may vary tremendously.

Instead, if it's stopped losing weight... it's DANGED DRY.

You've got 9 cubic inches of stock there, at 90 grams. That's 10 grams per cubic inch, or 17.28 kilograms per cubic foot.

When all your holly stock approaches that density in KG/cubic foot, it's DANGED DRY. :)

-- Tim --

Genuis
:)

[DCarr10760]

I think you are right.

You took the holly as it sits in your shop and weighed it, then danged dried it in the oven removing all of the water and weighed it again.

This differential represents the total amount of water present in the material as it sits in your shop now. Then you calculated the percentage based on your findings and I think that's right.

You don't mention if the material was air-dried or KD. Either way, depending on where you are in the world the level of humidity (ambient) may be very high and your wood may be moister than it would be in, say, January. Here in the Northeast where we've had a week or more of near-100% humidity I would guess that lots of stock has high moisture contents.

If the wood has been KD, or thoroughly air-dried and stable, and is now damp just because it is taking on water to equalize with atmospheric conditions, it is probably okay to use. Just don't build a big project and rush it into an dry air-conditioned house.

If it is still drying (as in seasoning) and is not yet stable, then wait.

All I've ever used holly for was stringing and inlay, small pieces like that aren't so critical I think because the amount of movement will be small.

Good luck with it!

David C

[Danford C Jennings]

Gecko,

The formula is correct.

As to the actual MC of the wood when it is being worked, it's far more important that it has reached equilibrium, this will depend entirely on what part of the country you live in and the environment of your shop.

Typically, kiln dried wood is dried between 10-12% but, once it leaves the kiln it will immediatly start to gain moisture. So, if you live in an area that averages around 60% humidity, 13.3% MC is dry...FWIW.

Dano

[Mark F]

You cannot find the resulting moisture content this way because you don't know the original moisture content. What you are calculating is the weight (due to moisture content) lost as a percentage of the final weight.
Your formula tells you that your resulting weight is 13.4% less than what you started with.

Mark F

[Gecko]

But doesnt that mean that 13.4% of the weight was moisture so the moisture content is 13.4%. Just trying to get a handle on this. Not just for the Holly but in genral as I am starting to air dry wood and wonder how to cheaply figure out the MC and what is acceptable MC to be able to use wood.

[Mark F]

OK, I see where you got your formula from and it is correct if you use it properly.

There is an explanation of the process of determining moisture content at the following http://www.ces.purdue.edu/extmedia/FNR/FNR-156.html

If you had a large board and wanted to determine the moisture content you could take a sample of the board and put it through your oven drying process, run your calculations and that would give you the moisture content of the remainder of the large board.

If this is what you were doing, then you were correct and I misunderstood. My apologies.


Mark F

[TDHofstetter]

Me, too - it works when you're figuring the MC of the REMAINDER... not of the board AS DRIED. :o

It's still not lab-exact, but it's sure close enough to get you ballparky. I'd round to the nearest percent or two & call it good. It'll fluctuate that much in your shop, surely, unless you've got some pretty good climate control.

EDIT: This should give you a pretty good ballparky figure of how much any boards of that species should weigh when they're squeechy dry... ergo how green they are when you buy 'em.

Seems to me there are some pretty extensive charts out there covering dry weight per cube for many & multitudinous species of wood.

-- Tim --

Genuis
:)

[Danford C Jennings]

Tim,

It's still not lab-exact...

I disagree, respectfully, of course....

The "oven method" of determining moisture content, which Gecko was using, is considered the most accurate method. Whilst not as "convenient" as a moisture meter, the pins don't always penetrate to the center; the oven method is essentially a volume measurement, weight. Since the sample is taken from the board, the oven method is extremely accurate in determing the MC of that board at the time the sample was taken. It only becomes inaccurate if the sample piece is too small or it sits around the "shop" a day or three before testing.....

Using this method, the wood has reached equilibrium when further samplings give the same results.

Dano

[Gecko]

"Using this method, the wood has reached equilibrium when further samplings give the same results"

So if I went and took another piece, say, a week later and did the test again and got the same results; then I could assume that the wood was "dry" and would now only change due to enviroment?