What moisture meter to get

[Scott T Smith]

Thanks everyone for all the advice. I do plan on building a solar kiln, but until then, the boards are air drying.

So to do the weighing method, I initially weigh the board and then over the course of drying, keep track of how much weight in water it's lost, right? Then how do I calculate the moisture content based on this information? I guess it would be the weight of the water lost divided by the dry weight, but how do I know the dry weight?

EDIT: Oh wait, if I were to use a digital moisture meter to check the wood when it's green, I could calculate the dry weight. So if for example the wood weights 10 lbs with a MC of 60%, then it would weigh 4 lbs when totally dry? Right?

Jay, weighing is usually the most accurate method. One thing to keep in mind is that moisture meters do not read accurately either below 7% or above 25% MC. Above 30%, there will typically be 10% variances between the true MC% and what the meter reads, as meters are not accurate above the fiber saturation point of the wood.

Most professional kiln operators use Delmhorst meters. The best RF type meters that I have found are the ones manufactured by Merlin in Austria. Not all RF meters are the same - they differ in terms of the depth that they can read to. An inexpensive RF meter (pinless) will only read 1/4" - 3/8" deep into the board; Merlin has a model that will read down to 1-1/2" (but it is around $400.00). If you invest in a high quality pinless meter, be sure to research the various detection depth models available and buy the one that meets your needs.

[Kent A Bathurst]

Scott...educate me here.

My very limited understanding tells me that I want to stay away from the very end of the board - like, maybe 6" or so in from the end? That is easy enough to do with my Delmhorst, but.......

To use the weight approach, if that is the case, it seems to me that I am going to keep having to chop away at a perfectly good board to get the proper section to cut and weigh. What am I missing in this picture?

thanks

kent

[Ron Bontz]

I use a J2000 and it seems to work just fine. I use it mainly for checking green turnings prior to putting it back on the lathe. Sometimes I will pick up some air dried lumber that I need to use it on. Also the company will give you conversion numbers as well for exotics if there is none built in already. I have had to do that on Amendium, "Brazilian Oak" No problems.

[Jay Bruckner]

Scott...educate me here.

My very limited understanding tells me that I want to stay away from the very end of the board - like, maybe 6" or so in from the end? That is easy enough to do with my Delmhorst, but.......

To use the weight approach, if that is the case, it seems to me that I am going to keep having to chop away at a perfectly good board to get the proper section to cut and weigh. What am I missing in this picture?

thanks

kent

I think you just weigh the entire board, am I wrong? I'm still not totally understanding how to find the actual moisture content by weighing.

Jay, weighing is usually the most accurate method. One thing to keep in mind is that moisture meters do not read accurately either below 7% or above 25% MC. Above 30%, there will typically be 10% variances between the true MC% and what the meter reads, as meters are not accurate above the fiber saturation point of the wood.

So how do you know what the true oven dry weight is? Average densities from charts times the volume of a sample board?

Most professional kiln operators use Delmhorst meters. The best RF type meters that I have found are the ones manufactured by Merlin in Austria. Not all RF meters are the same - they differ in terms of the depth that they can read to. An inexpensive RF meter (pinless) will only read 1/4" - 3/8" deep into the board; Merlin has a model that will read down to 1-1/2" (but it is around $400.00). If you invest in a high quality pinless meter, be sure to research the various detection depth models available and buy the one that meets your needs.

I think based on everyone's advice, that I should just use the weighing method, since it's the most accurate, and it's free besides. I just need to nail down how to do it.

[Scott T Smith]

Scott...educate me here.

My very limited understanding tells me that I want to stay away from the very end of the board - like, maybe 6" or so in from the end? That is easy enough to do with my Delmhorst, but.......

To use the weight approach, if that is the case, it seems to me that I am going to keep having to chop away at a perfectly good board to get the proper section to cut and weigh. What am I missing in this picture?

thanks

kent

Kent, what your missing is that if the board had a high quality end sealer applied to the ends (or better yet if the log had it applied before milling), the MC% should be the same weather you measure 2" from the end or 10".

Ideally, you want the board to dry through the face, not the ends, and end sealer helps to encourage this.

Even oven sample boards should have end sealer applied before drying.

[Scott T Smith]

I use a J2000 and it seems to work just fine. I use it mainly for checking green turnings prior to putting it back on the lathe. Sometimes I will pick up some air dried lumber that I need to use it on. Also the company will give you conversion numbers as well for exotics if there is none built in already. I have had to do that on Amendium, "Brazilian Oak" No problems.

That's a great meter; I use one myself along with the Merlin and an older 1000 series.

[Mats Bengtsson]

...To use the weight approach, if that is the case, it seems to me that I am going to keep having to chop away at a perfectly good board to get the proper section to cut and weigh. What am I missing in this picture?...

You do not miss anything, you just try to be practical. If you use a meter, it will give some incorrectness, but it will be good enough if the meter is good. If you use the "chop board" approach, it will give prefect results, assuming all the theory is correct (for example a guess made that the ends which you measured was similar to the parts you wanted to measure).

My advice is to be practical, use a meter, but not a too cheap one. Humidity is anyway going to change a bit as long as you do not manage to perfectly seal the wood, which even theroetically cannot be done with all kinds of finishes.

--- Mats ---

[Kent A Bathurst]

Kent, what your missing is that if the board had a high quality end sealer applied to the ends (or better yet if the log had it applied before milling), the MC% should be the same weather you measure 2" from the end or 10".

Ideally, you want the board to dry through the face, not the ends, and end sealer helps to encourage this.

Even oven sample boards should have end sealer applied before drying.

Got it. Stuff like that is why you are in your line of work, and I'm not.

[Bill Davis]

Here is a poll on moisture meters. Just click the "Vote Now" button to see results.
I frequently use the OD method when drying wood especially if a new species and I want to verify the meter reading.

Following is a procedure I wrote for a friend to calculate MC using a calculator and the OD method. You should use a sample of 100gm min and a scale with resolution of 0.1 gm or better.

When using an electronic calculator to figure MC, an easier formula is


%MC= [(Wet weight / Oven dry weigh)-1] x 100


Using a calculator

1. Enter the wet or current weight.
2. Enter ÷.
3. Enter the oven dry weight.
4. Press =.
5. The number displayer will be 1.xxyyyyyy
6. Mentally delete the 1. (.xxyyyyyy)
7. Mentally move the decimal point two places to the right . (xx.yyyyyy)
8. The MC is xx.y

Example:
If the current weight is 123.4gm and the OD weight is 99.4gm
Then 123.4 ÷ 99.4 = 1.2414
Removing the 1 and moving the decimal leaves 24.14% MC

Steps:

1. Measure and record the weight of a sample of wood preferably one whose weight is greater then 100 grams.
2. Oven dry the sample at 212˚F until the weight of the sample stops decreasing then weigh and record the weight.
3. Divide the weight obtained in 1 above by the weight obtained in 2 above.
4. Remove the ‘1’ and move the decimal two places and you have the MC of the sample when the first weight (wet weight) was taken.

A microwave oven can be used if proper procedures followed.

[Jay Bruckner]

Thanks Bill, that's very helpful. I think I understand the oven dry method now.

Guess I need to get a scale now. Maybe my thread should have been "what scale to get?"

[Mats Bengtsson]

Thanks Bill, that's very helpful. I think I understand the oven dry method now.

Guess I need to get a scale now. Maybe my thread should have been "what scale to get?"

Well, depending on wood to test, and wife, the question may also be "what oven to get".

--- Mats ---