The Forestry Forum

General Forestry => Drying and Processing => Topic started by: warren46 on August 29, 2013, 03:21:40 PM

Title: Moisture Meter
Post by: warren46 on August 29, 2013, 03:21:40 PM
I have a couple of stacks of red oak and walnut that have been air drying for about a year. I would like to get a reasonably accurate and reasonably priced moisture meter so I can determine if it is about ready to use.  I plan on selling some of this lumber so I want a good way to assure any customers that the wood is dry.  It is difficult to say how dry the lumber is given the rain and humidity we have had this summer.

I am sure there are many on this Forum that can offer good advice regarding moisture meters.
Title: Re: Moisture Meter
Post by: Den Socling on August 30, 2013, 10:56:50 AM
The first meter that comes to my mind is the Delmhorst J2000. It's a "stick" meter which means it has pins that you stick in the wood. They cost around $300. For thicker wood, you can add a slide hammer with longer pins.
Title: Re: Moisture Meter
Post by: scsmith42 on August 30, 2013, 12:12:05 PM
And if you prefer a pinless meter, the Merlin's are really nice.
Title: Re: Moisture Meter
Post by: woodman58 on August 31, 2013, 06:58:23 AM
If you are selling this wood to be used for inside use (furniture, etc.) it will never be ready. The moisture content in air dried lumber in your area will be about 15%. This is to high to build furniture. It should be between 6 & 8%. Years ago it was O.K. to use air dried lumber for interior furniture but, today most households are climate controlled. They don't let the humidity from outside in. If you build furniture at 15% moisture and bring it down to 6% in a home it will cause shrinkage and loosening of glue joints. I would see about building a solar kiln to bring the moisture down to 6% to 8%. You can also tell your customers to sticker the wood in their basement with a dehumidifier to get the moisture down.
Title: Re: Moisture Meter
Post by: warren46 on September 01, 2013, 03:13:27 PM
Thanks for the suggestions.  That is what I needed.

Title: Re: Moisture Meter
Post by: POSTON WIDEHEAD on September 03, 2013, 07:16:39 PM
Warren, I bought a MM from LOWE'S. It was less than $30.00.

I know nothing about MM's but bought this one just for fun and it does read M-content but I don't know how accurate it is.

What ever you buy, bring it to the mill next time you come and we can make a comparison between the 2 meters. I have some 2 year old Walnut we can poke'em in.
Title: Re: Moisture Meter
Post by: warren46 on September 03, 2013, 08:31:03 PM

I have not purchased on yet but I will bring it with me to your place next time I come after my purchase.

Title: Re: Moisture Meter
Post by: Kingcha on September 03, 2013, 09:51:30 PM
I to bought and inexpensive mm.   Seems to work fine so far, though I have no idea about its accuracy.

Title: Re: Moisture Meter
Post by: WDH on September 04, 2013, 07:58:02 AM
This is the one that I use.  It is pinless.  I did not like the little snake-bite holes in my good hardwood lumber.
Title: Re: Moisture Meter
Post by: red oaks lumber on September 04, 2013, 09:42:00 PM
for quick  moisture readings i use a ligomat  2 pin meter. its accurate but, on rough lumber the pins dont penetrate far enough to reach in.
when i'm checking wood in the kiln or other places where the wood should be dry i use a delmhorst hammer style meter with pins that are over an inch long.
 these are my thoughts ... if your dealing with dry wood, how much is your reputation worth?  don't be cheap on the meter.
Title: Re: Moisture Meter
Post by: GeneWengert-WoodDoc on September 05, 2013, 06:32:46 AM
To choose the correct meter, you need to define your needs.  This would include how dry your wood will be, whether you want core MCs or just an average, how accurate the readings must be and so on.

The best meter is the same one that your customer will use.  This is because different meters will give you different readings.  This is especially true for meters that cost under $200.  One approach is to specify that the basis for MC determination with what lumber you are selling is the meter model # made by _____.  Appreciate that the term "kiln dried" has no particular MC associated with it.  You need to give the actual numbers.

If selling furniture grade wood, the desired MC for hardwoods is not wetter than 7.5% MC or drier than 6.5% MC oftentimes.  For softwoods, no wetter than 12.0% drier than 10.0% MC, except that construction grades are oftentimes 15% to 19% MC.

But are these values the average or the MC at any spot (core, shell, end, middle, etc.)?  The pin meters with insulated needles measures at one spot (where the tips of the needles are), while the pinless meter measures an average volume, with a bit heavier emphasis on the wood closest to the measuring instrument.  Pin meters aare sensitive to temperature with a 1% correction for every 20 F.  Pinless are sensitive to density with slightly higher densities giving a higher MC than actual.  The pin meter has trouble under 7% MC while the pinless can go to 4% MC.  Neither meter can go above 28% MC with any accuracy.  The pinless is fast and can scan a large area; the pinless is slower.  Both have long probes for reaching into a stack of lumber on stickers.,,Wagner and Delmhorst meters.

Which meter is best?  One that is used...following the mfr's instructions and with a fresh battery.

Note that what one meter has trouble with, the other type covers well.  So, actually, together (pin and pinless) you have the best.  So, how important is the MC?  Will pieces be rejected by the customer if they are too wet or too dry?  Will a piece with incorrect MC reflect negatively on your reputation?

A good question is how easy will it be to get service...repairs or maintenance?

If you are going to get just one meter, Den;s suggestion of the J-2000 with the 26ES probe is a pretty good as it will work well in almost all situations and many customers will have the same meter.  However, pinless meters (Wagner and Delmhost both have popular models) are also fair good choices.  (Special note:  Delmhorst is coming out with a new pinless model in the next month and this might be worth waiting for.)

If you do take MC readings, it is often a good idea to write your readings on the piece of lumber.  This assures your customer that you have indeed checked the MC and the MC is perfect. 

Also, remember that the core MC will not change for many months after the wood leaves the kiln (most of the time), so the core MC is the MC when the wood left the kiln, even if the customer has stored the lumber at a higher moisture condition than desired  which can cause the shell MC to increase beyond the desired value.  In this case, a pin meter with insulated needles is a key piece of equipment.
Title: Re: Moisture Meter
Post by: warren46 on September 10, 2013, 05:40:51 PM
I have a related question.  Can the moisture content of wood be determined using the following method?

Cut a section of wood into thin strips and carefully weigh a sample of about one pound.

Desiccate the sample using either an oven or vacuum chamber until all moisture is removed.  This end point can be determined by weighing the sample at reasonable intervals and noting when the weight of the sample no longer decreases.

Subtract the final weight of the dry wood from the original sample weight.  The moisture content is the difference between the two weights divided by the weight of the final sample.

Is this a reasonable way to determine moisture content without a meter?

Will my wife be OK with baking wood in her oven ::)
Title: Re: Moisture Meter
Post by: Ianab on September 10, 2013, 06:01:15 PM
Yes, "oven drying" is actually the most accurate way to measure moisture content, and that's what's used to actually calibrate the electronic meters, which only ever give an approximate measurement anyway.

You can use an oven on low heat, and just bake the sample until it stops loosing weight. At that point you know it's "bone" dry (0% water),

Compare the weight now with the original weight, and you know how much water has gone, so you can work out what the original % was.

A microwave will also work, but you have to be careful not to set the wood on fire. Small bursts of zapping, then let it cool again. The microwave will also smell like wood sap afterwards, so best not to do it with the wife's kitchen machine.  :D

Of course this is more time consuming than just poking a piece of wood with a meter, but it will work.

Title: Re: Moisture Meter
Post by: GeneWengert-WoodDoc on September 11, 2013, 08:39:37 AM
If you put a wood sample in a microwave and use a rotating tray with no pieces touching each other and med low power, you have almost zero risk of causing the samples to over-heat and start smoking.  For example, see DRYING HARDWOOD LUMBER for this procedure.  It does not matter how you oven dry--hot air at 215 F or microwave--to reach 0% MC.  Both methods will reach the same final MC and weight, so both are very accurate.  The problem arrises when you over heat the sample in the microwave from using too much power.  This causes more than just water to evaporate, so your final weight is in error.  But with the correct procedures, etiher works well.  However, the microwave is around 30 minus while the hot air is often 24 hours or so.  Both are "done' when constant weight is reached.  A smoked sample is not going to give the correct answer.

In DRYING HARDWOOD LUMBER, the appendix has a comparison of pin and non-pin meters.  You will see that they are generally within 1% of the true MC, but sometimes they were further off.  The pin meters work only between 6.5% to 28% MC; pinless, 4% to 28% MC.  Although the final MC is very important, almost all drying defects are initiated above 45% MC, and so the meters cannot be used at this MC level to monitor drying rates and control drying defects.  So, the oven-drying method using kiln samples is the key.
Title: Re: Moisture Meter
Post by: beenthere on September 11, 2013, 10:55:14 AM
Here is a publication in .pdf format.
Title: Re: Moisture Meter
Post by: warren46 on September 11, 2013, 12:15:54 PM
Thank you for all of the replies.  I will study the Drying Hardwood Lumber literature for more answers.