ERC moisture content scale

[kelLOGg]

I have a Protimeter Pin type moisture meter and the booklet that came with it has no scale for ERC (or juniper) so I opted to use that for western red cedar. I don't trust my readings for ERC: I put air dried RO, WO and ERC in the kiln almost 2 weeks ago and the RO reads 9.6, WO 10.5 and the ERC 12. (measurements were taken at the core). 
The oak readings look reasonable but the ERC is not. There must be a hundred or more species listed in the booklet and the scale to use. What is the best substitute for ERC? 

The ERC is for a customer who is building indoor cabinets and needs it airdried and it is taking far longer than I expected.

[doc henderson]

I would get a sample and do an oven dry calculation, if you can spare a small chunk.  does it feel light when you pick up a board.  do you have access to a pin-less meter to compare.  I know my wagoner has a density setting for ERC.  I guess a less dense wood could have a higher MC at a given RH by definition.  since MC = wt. of the water/wt. of the dry wood.  so same amount of water but a smaller bottom number (denominator)  gives a higher MC.  @GeneWengert-WoodDoc 

[GeneWengert-WoodDoc]

ERC has many common names including aromatic cedar, juniper, eastern juniper, and more.  

If you do an oven test, drive the pins 1/4 of the thickness, not to the core.

[kelLOGg]

Doc,
I'll look into the oven dry method. A gas fired oven sounds risky - maybe a microwave? In the past I neighboring sawyers let me use their meters but I try to restrict travel now.

Gene,
The booklet has none of those other names for cedar :(.

What's the idea behind driving pins in 1/4 way. Seems like the midpoint would be better.

[btulloh]

A microwave oven is the best thing to use, but don't use the one in your kitchen.  You can usually pick one up for free or close to free.  It's best not to do it in the house because of the fumes that can come off the sample you're drying.  A small kitchen scale is cheap and accurate enough for weighing the dried sample.  

[GeneWengert-WoodDoc]

A microwave can be used, but you need a carousel trey and then use med low lower to avoid smoking the moisture section.  Drying time can be 20 minutes or so.

The 1/4 depth gives the average, which is also what the oven test uses.

[kelLOGg]

btullah, I was wondering about a kitchen scale. Thanks.

Gene, I can see that a 1/4 depth gives the average. I was trying to go for the target MC% at the toughest spot to reach. I guess that is unnecessary effort. Thanks.

[btulloh]

If I remember correctly, the resistance measurement for a given species correlates to specific gravity.  There are plenty of charts around that will give you the specific gravity of every species on earth. Find ERC in that chart and then find a species that is listed for your meter that has the same SG.  Bingo, you've got the mc correction you need to get an accurate reading. 

[doc henderson]

@kelLOGg I used a small electric convection oven, think pizza oven.  you want it at just above boiling  (217°F).  the scale I used is the same as I used for the pinewood derby cars I made my son.  used to get them on amazon and measure in grams or ounces.  the calculation seem tricky because you are looking at a ratio of weight of the water to the weight of the dry wood.  so MC can be greater than 100%.  @GeneWengert-WoodDoc has the calculations in the drying hardwood lumber article.  you get the wet of a small chunk.  record the weight and label the pieces if you are dong more than one piece.  keep drying until it stops loosing weight.  the final weight is the dry weight of the wood.  take the wet wt. minus the dry weight and that is the weight of the water.  now divide the water weight by the dry weight and there you go.  The reason for the depth of the pins.  you can measure surface, average or core MC.  the difference is the depth of the pins.  1/2 way through the board is core, so 1/4 is average and surface is surface .  If wet to dry. the board dry weight is 1/2 the original weight, the wood was at 100% MC.  If you get the weights, post them so we can see what you got, and compare it to your readings.  ERC is very forgiving as well so your client will prob. be ok.  specific gravity is just density relative to water.  I agree with looking that up or density and find a like correction factor.  a digital scale should work.  the old spring type not so much.  

[GeneWengert-WoodDoc]

For many years, the pin type moisture meter used throughout the country On US species e was only one calibration and that was for Douglas-fir.  Except for Southern pine, the corrections for most species were insignificant.  This is true for aspen (low density) through hickory (dense).  

[kelLOGg]

btullah, black gum and elm have the same densities as ERC (35 lbs/ft^3) and their scales give almost the same MC% for ERC as does the western cedar scale (10.8 to 11%). My cedar is just not drying :( whereas the RO and WO are - they are down to 7.9 and 8.6%. I'm using the same pin for each species. Its getting to be a drag to open the kiln and reinsert the pins in each species. I talked to the ERC owner and we agreed to let it keep "drying" a few more days. Fingers crossed but ...

[btulloh]

That's interesting.  Dealing with mixed loads is way out of my experience, but I hear it's problematic from the veterans.  Seems to me the cedar would be losing mc faster than the the WO and RO, but I'll just have to leave that discussion to the veterans.  I hope it all works out, and it's an interesting thread to follow.  

From my past experience with ERC, I'd think that 10% will be ok even for cabinet use.  After it sits in the shop and stabilizes it's probably going to be somewhere around that anyway.  On another subject, I haven't heard anyone talking about setting the pitch in ERC, but it seems like it would be a good thing to do.  

[btulloh]

I am curious about that scale that Doc mentioned.  The little kitchen scales are good for weighing the oven-dried sample, but mine maxes out at 5lbs and is not that useful for some of the kiln samples.  @doc henderson can you maybe provide a link for that scale you've got?

[doc henderson]

I will get a pic, but got it on amazon.  most oven dried samples should be small like several hundred grams, or about 10 ounces.  I think the pic in the drying hardwood lumber is a 4/4 board, cut 1 inch long and the width of the board.  so hopefully some wood can be sacrificed.  if not carry on.  the scale is a small one that would fit in your pocket and runs on AAA batteries.

[btulloh]

It's the kiln sample that has some weight to it and is a couple feet long.  The kitchen scale, or even one of my reloading scales is perfect for the oven sample.  Doc,don't worry about the link, I thought you were talking about a larger scale.

[doc henderson]

great,  yea the reloading scale is great, just cut a small sample to weigh, dry and re-weigh.  to use the bigger sample, you would need and original weight with a known moisture, and re-weigh the same way to see the MC loss.

[btulloh]

You might want to re-read the part about the oven dry method. 

[doc henderson]

ok.  I have been up all night.  I would recommend using a small chunk to compare the current mc reading you are getting with an oven dried sample.  I thought you were wanting to use the larger board?  

[btulloh]

You might want to re-read the part about the oven dry method.  

[btulloh]

Stay safe, Doc. These are unusual times. 

[GeneWengert-WoodDoc]

The resistance of wood using needles is given in Yanle 1 of the following report.  If you look at hardwoods, you will see that highest resistance is in Tupelo and aspen, yet they have a big density difference.  The lowest resistance is from ash, and basswood.  Aspen and basswood are close in density but far apart in resistance.

Unfortunately, these data do not have ERC?  The Delmhorst species correction table has ERC and cherry very close.

https://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr06.pdf

The pinless meter is very sensitive to density of the wood, but density does not affect the pin meter.

Note also that ERC and western red cedar are not  closely related as they are different genus

[btulloh]

This is a bit of overkill for this thread, but since we were discussing the oven dry method I'm going to add these links.  

The first link is to the VT Solar Kiln plans which has a good but concise description of using the oven-dry method for monitoring the mc of a kiln load.  This is a good and complete explanation of the process and is written in a way that most will find useful.

The second link is to a publication by the Forest Products Laboratory of the US Forest Service.  It is thorough, detailed, provides background information, and an elaborate description of the same process described in the VT Solar Plan document.  Enter at your own risk! Don your PPE and be prepared for eyes glazing over.  But it is thorough.

VT Solar Kiln Plan  - the oven-dry method is covered on pages 5 and 6.

USFS FPL Chapter 6 - Kiln Samples - the main course can be found on pages 120-124, with appetizers on pages 117-124, and desert on pages  125-137.  (This chapter begins at page 117 of the entire document.)

So there are the links to process of using kiln samples and the oven dry method for monitoring mc in a load.

===

Generally most of us use pin meters to monitor the mc, which are more convenient.  The oven dry method is almost as convenient after the initial preparation.  I found it to be a valuable learning experience to use the oven method a few times.  It also gives a good idea of how well your meter is performing, and also let's you know if you're using the pin meter properly, since methodology is important  with meters.

My opinion on drying moisture samples (for us home users) is that the microwave oven is the best way to go.  Using a conventional or convection oven takes up to 24 hours (or more) to complete the drying of the moisture samples.  Without having a purpose-built oven with proper safety features, I wouldn't want to use the conventional oven method personally.  Your risk tolerance may vary.  A microwave will do the same job in an hour or less.  It also should be attended, but there's always something to do in the shop to pass the time.  With either type of oven, you really don't want to do this in the house because of the smell and fumes that can be produced.  No doubt your wife would agree with this.  Strongly, in most cases.

One really good reason to use the oven dry method is if you really want to determine the initial mc of your lumber if it is >30% mc, since meters don't provide useful readings at mc much above 30%.  Most of us air dry first before running a load in the solar kiln, so not a big issue.  I do want to try this with a load of SYP right off the saw, but so far haven't had the opportunity.  Not essential - just a matter of curiosity for me.

A final note:  You can check the mc of a load by removing a board from the pack and cutting a moisture sample, and use the first phase of the process (preparing moisture samples).  This would be inconvenient at best for monitoring progress, because you would have to remove another board and process another moisture sample every time, but it could be used to confirm the mc at the end if you were in doubt.  

So anyway, the links are there if anyone is interested.

[doc henderson]

I re-read all the oven dry stuff and agree with what you have posted and myself as well.  @btulloh 

[kelLOGg]

This AM the kiln finished the sterilization cycle; the oaks came out reading in the mid 6% range and the ERC finished at 10.1% as measured on the WRC scale. I don't trust the ERC numbers but I am sure my customer won't have bugs in his kitchen and that the lumber is dry enough for indoors. 

I am going to look into a microwave oven for MC determination so I have a backup plan if this confusion repeats itself. There's a lot of good info on this in this post and the FF in general. Thanks for all the responses.

[Cedarman]

If you overdry ERC (5 to 6%) you will see side bend in your boards and planing will be a nightmare.  I have used a pinless Wagner meter for 25 years.  Air dry is 12%.  Summer can get to 10 to 11 if sitting in a shed.  We dry with heated air from outdoor wood stove and get to 8 to 10%. Up to 8000' at a time.  Never get temp over 90 to 100  degrees.  When sawing cedar logs that have set for a few weeks you will notice that you do not get pitch on your sawblades.  So pitch in cedar is not a problem even in air dried wood.  ERC shrinks the least of our species, so drying to 10% will yield good manufacturing results.
If you heat ERC too high you will boil the oils off and there goes your aroma.
Notice if you flat stack your dried wood you will see a white fuzz between boards.  Look close, you will see crystal needles. Condensed cedar oil.  Evaporates on exposure to air.
Once you do the microwave tests and find the true MC, then compare to your meter reading, you will know the fudge factor and have confidence in how much your meter is off from true reading.
I like the pinless because I can quickly scan a board and see the wide variations from sapwood to heartwood, knots and from board to board. A board while drying can be 12% MC heartwood and 20% in the sapwood. I am looking for equalization between sapwood and heartwood.
Takes about a week to 2 weeks to dry from green to 8 to 10%.
Never mix with other woods, so don't know how drying is affected in this situation.

[GeneWengert-WoodDoc]

PUt your meter on the cherry scale and see what readings you have.

[D6c]

Experimented with doing microwave drying of ERC samples yesterday.  The old microwave I have probably has hot spots worse than newer models but it does have a turntable.
First samples I set the power on 50% and 10 min to start.....waaay too hot....turned them black and just about set them on fire.
Second try at 20% power was still a little hot and made one darkened spot.
Third try at 10% power worked ok.....I heated it at 10 min intervals to check for overheating.  Gets pretty hot at first but as moisture gets lower the wood temp drops.  Ran it for an hour total, checking weight 2-3 times, then another 10 min to see if it had stopped getting lighter.

Using my old reloading scale for now, but a digital scale with a larger capacity will be needed.
Moisture calculation on the two samples averaged around 11 1/2%.

I cut the samples out of the center of a board and saved a kiln sample and sealed it's ends.  (used clear silicone since that's what was handy)  Weighed the kiln sample on my postal meter and put it back in the kiln.

In reading Cedarman's post above I'm probably letting the kiln get too hot.  A couple of days it's gotten to 125°.  In a solar kiln I can see it will be hard to keep the temp down this summer if it's getting that hot already this spring.

[doc henderson]

to keep the kiln cooler you can cover part of the glazing, and or open the vents more.

[GeneWengert-WoodDoc]

For measuring ERC with a pin meter, are you using the black cherry scale?

[kelLOGg]

Gene, my customer picked up his cedar before you posted your recommendation so I'll experiment with my own ERC. 

[kelLOGg]

I opened the kiln and inserted the pins in a piece of my air dried ERC. On the cherry scale I measured 12.6% MC and on the western red cedar scale I measured 11.7%.