LumberJocks

Moisture meter

  • Advertise with us

« back to Hand Tools forum

Forum topic by Woodcut1 posted 03-27-2016 11:37 PM 811 views 0 times favorited 10 replies Add to Favorites Watch
View Woodcut1's profile

Woodcut1

34 posts in 291 days


03-27-2016 11:37 PM

I am still a little confused about moisture meters. Most pin type say measurement depth is only a sixteenth or an eight of an inch deep or so. I want to know what the moisture is in the middle of a two inch slab or a turning block that could be six to eight inches thick. How does a moisture meter tell me that? Thanks for any input on this.
Tom


10 replies so far

View waho6o9's profile

waho6o9

7179 posts in 2044 days


#1 posted 03-28-2016 12:21 AM

https://woodgears.ca/lumber/moisture_meter.html

HTH ^^

MM (moisture meters) can get expensive and it seems the more you spend the

better they are. If it’s crucial in your line of work I’d be worth it for a good MM.

I just ask the lumber yard and they tell me and I’m good to go.

Interesting topic though.

View rwe2156's profile

rwe2156

2200 posts in 948 days


#2 posted 03-28-2016 11:27 AM

After watching Wandel’s review I’m pretty convinced I don’t want a pinless meter because of all the conversion factors for different wood plus the results seemed inconsistent.

-- Everything is a prototype thats why its one of a kind!!

View JBrow's profile

JBrow

819 posts in 387 days


#3 posted 03-28-2016 05:28 PM

Woodcut1,

I believe you are correct, that a pin-style electronic moisture only gives reasonably accurate moisture content between the pins and hence at the surface being tested. The resistance of DC current is measured mostly between the pins. Therefore, testing the surface of a slab of wood may not give accurate moisture content in the center of a slab of wood.

On the other hand, given the dynamic nature of moisture movement in wood, the surface readings may be indicative of the moisture content in the center of a piece of lumber. A test could reveal to what extent the surface readings of a moisture meter are indicative of the moisture content in the center of a piece of large format lumber. The test requires averaging a set of moisture meter reading on the surface of a piece of lumber. The lumber is then crosscut to expose the interior of the wood in the area where the surface readings were taken. Then moisture meter reading are taken at the fresh cut near the center of the lumber. My guess is that the larger (thicker, wider and longer) lumber will show a greater variation from surface reading than 4/4 lumber.

If surface readings are not indicative of interior moisture content, then how can moisture content in the center of lumber be determined? That question intrigued me, so I did a little web research and some thinking. I concluded that testing the center of a hunk of wood for moisture content can be done using either destructive methods or perhaps by an approximating non-destructive method. For what it is worth and if you are interested, here is what I found:

Various methods for measuring the moisture content of wood are described by the American Society for Testing and Materials in publication ASTM D4442. I suspect these methods are used in the wood industry. I also found this very understandable and a fairly easy and informative read in the web article entitled “A PRACTICAL GUIDE FOR THE DETERMINATION OF MOISTURE CONTENT OF WOODY BIOMASS A Practical Handbook of Basic Information, Definitions, Calculations, Practices and Procedures for Purchasers and Suppliers of Woody Biomass “ by Robert Govett, University of Wisconsin-Stevens Point, Terry Mace, Wood Utilization and Marketing, Wisconsin DNR, Scott Bowe, University of Wisconsin-Madison. This article is found at:

http://dnr.wi.gov/topic/ForestBusinesses/documents/BiomassMoistureContent.pdf

Summarizing some of the article, moisture content is determined on one of two bases. The first is called GREEN BASIS:

MC% (Green basis) = (weight of water/(weight of water + dry weight of wood)) X 100%

The second basis is called OVENDRY BASIS:

MC% (OD basis) = (weight of water/(dry weight of wood)) X 100%

Pin style moisture meters rely on the relationship of resistance and water content in the wood. According to the article, most pin type meters readily available in the U.S. indicate moisture content on the OVENDRY BASIS. Instructions that come with the moisture meter may disclose the basis used.

Destructive methods for determining moisture content require a sample of wood for testing. Drilling a hole through the slab near the area where the moisture content is sought and collecting the resulting dust can provide a sample for testing. The sample could then be used following one of the standard methods for determining moisture content. Since these destructive methods take some time and equipment and are probably more involved than most wood worker would like, it is not very practical.

A non-destructive method can be used but this method relies on the Density of “dry” wood. Since Density is Weight divided by Volume and the Volume of wood changes with its moisture content, it will only give approximate (maybe good enough) moisture content of the entire piece of wood. I found the Density of various “seasoned & dry wood“ at:

http://www.engineeringtoolbox.com/wood-density-d_40.html

As used in both calculations of moisture content below:

Volume = Length X Width X Thickness of a piece of wood. I would think error in the Volume measurement is reduced if the surface of the wood has a low moisture content; otherwise the Volume would be larger than the corresponding Volume if the wood is dry; making the Volume unreliable in the calculations below. This assumption relies on the belief that the surface moisture content is a good enough indicator of low moisture content in the center of the wood.

Weight of the Wood = the Weight of a piece of wood with a given measured Volume, as used when multiplying “Volume X Density”.

Weight of the Wood = Weight of Water in the Wood + Dry Weight of the Wood.

The formula I derived corresponding to moisture content using the GREEN BASIS is:

Moisture Content (GB) = ((Weight of the Wood – Density X Volume)/Weight of the Wood) X 100%

And for the OVENDRY BASIS:

Moisture Content (OD) = ((Weight of the Wood – Density X Volume)/(Density X Volume)) X 100%

Therefore, measuring the volume and weight of a piece of wood thought to be relatively dry and plugging the measurements into the formulas may give a good non-destructive approximation of the overall moisture content of the wood.

View Steveayerse's profile

Steveayerse

4 posts in 231 days


#4 posted 04-24-2016 07:30 AM



I am still a little confused about moisture meters. Most pin type say measurement depth is only a sixteenth or an eight of an inch deep or so. I want to know what the moisture is in the middle of a two inch slab or a turning block that could be six to eight inches thick. How does a moisture meter tell me that? Thanks for any input on this.
Tom

- Woodcut1

Hello woodcut1, I have recently posted about moisture meters in my blog, because I recently had an experience testing many of them, so I think it may be useful for you: Here is my blog post

-- Read my personal blog and learn from my mistakes and success about woodworking!

View Wildwood's profile

Wildwood

1887 posts in 1602 days


#5 posted 04-24-2016 12:29 PM

Think moisture meters can give you ball park MC percentages whether buy pin or pin less. Bought a General tool & instrument pin meter from Lowe’s several years back for less than $10.00 when that meter a darling of all woodworking message boards. Up until few months ago could buy that meter for $30 now see it selling for $80. Buy what ever you can afford but do read user reviews first!

http://www.lowes.com/pd_546043-56005-MMD5NP___?productId=50102606&pl=1&Ntt=moisture+meter

Ball park moisture content percentage gives you a starting point and where you must get to before building with your wood. Knowing average MC% based upon where you live and whether building for inside outside important. See page 5 and figure 13-1 and table 13-2 on the same page.

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr190/chapter_13.pdf

Whether kiln dried or air dried wood will always seek a moisture content based upon relative humidity inside or outside. While air drying out side will get you down to a certain moisture content based upon where you live might have to bring it in the shop or indoors to obtain workable MC before working.

If kiln dry wood but leave outside for a day on a rainy day may find need to let it rest awhile inside. Because not dealing with old growth wood rough cut one day and finish cut after glue up or couple days later base on components.

Forget 1” per year rule of thumb!

-- Bill

View pintodeluxe's profile

pintodeluxe

4859 posts in 2281 days


#6 posted 04-24-2016 08:05 PM

Just trim an inch or two off the end of a board to get a core moisture reading with a pin style meter. I prefer pin style meters because I am usually measuring rough lumber, and pinless meters require you to plane a section of lumber smooth for accurate results.

I use a Lignomat Mini E/D. It gives consistent readings. The previous meter I had was a cheap-o and would vary by 5-7% in the same spot.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View jdh122's profile

jdh122

879 posts in 2285 days


#7 posted 04-24-2016 09:51 PM

I have a cheapo pin meter, no idea if it gives really accurate readings. But I just take a piece of wood that I know is in moisture equilibrium in my shop (ie one that has been there for a long time) and take a reading on it. Then compare that to the piece I want to know the moisture content of.
Never thought about trimming a bit off the end, that’s a good idea…

-- Jeremy, in the Acadian forests

View Woodcut1's profile

Woodcut1

34 posts in 291 days


#8 posted 04-25-2016 12:12 AM

Thanks everyone for all your thoughts and formation concerning moisture meters.I learned a lot on your blogs and links to information sites. I like the idea of measuring known dry wood in your shop and then measure the wet wood and track it from there. I am not sure you can crosscut lumber and measure it that way because pin type moisture meter does’t measure end grain accurately. I suppose in many cases you can use the destructive method and a point in the wood where you know you will be cutting at that point. This is all good for demensional lumber drying and working with that wood. As far as I can tell it looks like for thick woodworking blanks it is just as easy to use the weighing method.
Thanks again,
Tom

View Steveayerse's profile

Steveayerse

4 posts in 231 days


#9 posted 04-25-2016 02:47 PM

I am glad that we can help you! Have a nice day!


Thanks everyone for all your thoughts and formation concerning moisture meters.I learned a lot on your blogs and links to information sites. I like the idea of measuring known dry wood in your shop and then measure the wet wood and track it from there. I am not sure you can crosscut lumber and measure it that way because pin type moisture meter does t measure end grain accurately. I suppose in many cases you can use the destructive method and a point in the wood where you know you will be cutting at that point. This is all good for demensional lumber drying and working with that wood. As far as I can tell it looks like for thick woodworking blanks it is just as easy to use the weighing method.
Thanks again,
Tom

- Woodcut1


-- Read my personal blog and learn from my mistakes and success about woodworking!

View pintodeluxe's profile

pintodeluxe

4859 posts in 2281 days


#10 posted 04-25-2016 04:08 PM



Thanks everyone for all your thoughts and formation concerning moisture meters.I learned a lot on your blogs and links to information sites. I like the idea of measuring known dry wood in your shop and then measure the wet wood and track it from there. I am not sure you can crosscut lumber and measure it that way because pin type moisture meter does t measure end grain accurately. I suppose in many cases you can use the destructive method and a point in the wood where you know you will be cutting at that point. This is all good for demensional lumber drying and working with that wood. As far as I can tell it looks like for thick woodworking blanks it is just as easy to use the weighing method.
Thanks again,
Tom

- Woodcut1

As far as your concerns about measuring end grain with a pin style meter…
Lignomat recommends making a fresh cut in the lumber and measuring end grain for core moisture content on boards 5/4” and thicker. I usually work with 5/4 rough lumber, and this is my standard practice. I find very similar readings in end grain, and long grain (both side and edge readings).

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics

HomeRefurbers.com