Good moisture check method?

[D6c]

How valid do you think this method of checking moisture checking thick slabs might be?
I drilled two pairs of 3/16" holes in a sample, one about 1/4 the thickness, and the other 1/2 the thickness of the wood.

I drove pairs of nails into the bottoms of the holes and centered them in the holes so only the tips are touching the wood,
then used my Delmhorst meter on the nails to get 3 readings.
On the surface with the meter probes and then two readings and depths of the nails.

On this sample I got 8.3%, 9.1%, and 10.1%.....higher moisture readinigs deeper in the wood as expected.

Would this be a decent way to check the oak slabs I have in the kiln?  If so, I figured I'd set pairs of nails in a couple of places
and seal around the nails with a little silicone to prevent moisture from working out of the drilled holes and skewing the readings.
Then I could periodically check the nails to see how my drying is coming along.

How close to the end of the lumber could I place the nails without too much error?  I will probably trim the ends later but don't really want to trim off too much or have holes that are near the middle of the slabs.




 

[Stephen1]

I am going to follow along for sure. I can see siliconing around the nails to keep the moisture .Would the nails skew the electrical function? 

[D6c]

I am going to follow along for sure. I can see siliconing around the nails to keep the moisture .Would the nails skew the electrical function?

That's part of what I'm not sure of.  In my test piece I have two sizes of nails but on the slabs I'd keep them the same.
My thinking was partly that if you can add an attachment like this to the meter without affecting the reading then the nails might be ok.  Electrodes For Moisture Meters | Delmhorst

[GeneWengert-WoodDoc]

There is nothing technically incorrect with your method.

[Walnut Beast]

Your not going to get a accurate reading at the depth you want. They have a coating on the pins and that coating keeps the reading down to the specific point in the wood. So if you use a nail you won't get the reading to the specific point. How I know this. When I called and asked them how do I know when to replace the pins. They said when the coating comes off 🤔

[YellowHammer]

Yes, in order to measure at specific depth, all but the tips of the probes should be electrically insulated.  

[kelLOGg]

What is the conductivity of your silicone? Some silicone rubbers release acetic acid during curing which is a conductor (relative to wood). Do a test by filling 2 holes with nothing but silicone and touch your electrodes to the silicone. If it is an insulator then you won't get a reading and your method will work. If you get a reading select another adhesive/filler that acts as an insulator. 

[customsawyer]

I would get the sliding hammer from Delmhorst with the insulated pins.

[D6c]

I would get the sliding hammer from Delmhorst with the insulated pins.

I may get one but in this case I'm trying to limit the number of holes I make in these large slabs.

[D6c]

What is the conductivity of your silicone? Some silicone rubbers release acetic acid during curing which is a conductor (relative to wood). Do a test by filling 2 holes with nothing but silicone and touch your electrodes to the silicone. If it is an insulator then you won't get a reading and your method will work. If you get a reading select another adhesive/filler that acts as an insulator.

I'll have to check that, or make sure I cover the nail with shrink tubing.

[K-Guy]

Watching these may help.

KilnIQ Episode 3: Moisture Meters - YouTube

KilnIQ Episode 5: Sample Boards - YouTube

[D6c]

Watching these may help.

KilnIQ Episode 3: Moisture Meters - YouTube

KilnIQ Episode 5: Sample Boards - YouTube

I understand about taking moisture readings and using kiln samples.  It's just in this case I can't cut samples out of the middle of an oak slab that's 3 1/2 ft wide x 13' long without ruininig a valuable slab, nor do I want a lot of pin holes from taking moisture checks every couple of days.  Also, from what I read the pinless type meters won't read deep enough to get good readings in a slab that's 3"+ thick.
That's why I was trying the nails so I check moistures at the same locaiton multiple times.

[customsawyer]

I often use the same holes on high dollar slabs with the sliding hammer.

[WDH]

I use the same holes, too.

[Don P]

You could use insulated pins and just leave them in. I've seen big kilns just use nails and clips in the kiln. I'm wondering though whether they need to be insulated to read the higher core moisture. Electrically isn't the pin going to read from the wettest point, which should normally be at the tips in the wetter core? Or, do we care where that easiest electrical path/wettest point is, it just needs to be dry.

[btulloh]

Seems like stainless steel or aluminum nails would be required, especially on oak.  I've used nails in the past without doing anything other than driving them in to a controlled depth and it seemed to work fine.  Confirmed it by the kiln sample oven dry method, which was possible for the stuff I was drying and testing.

I'm no where as experienced as some of you guys so this is an interesting thread for me to follow.

[YellowHammer]

From a thick board standpoint, an edge is just a narrow face.  So I'll drive my pins in from the edge, especially if it is a live edge slab, right through the bark where the holes won't be seen.  That's why it's important to use insulated pins.  

The measurement difference between a thick edge and face is negligible with a thick boards, and as an end of cycle confirmation I will check from the face, in a spot I will cut off later at the end of the drying cycle.

Once the board is essentially dry, the readings, even from the ends, will start to consolidate and come together, although checking from the ends is the least accurate place to measure when the board has moisture in it.  

Of more importance when using a pin resistance meter is the distance of the pins.  However, as the moisture drops most of the errors bands will narrow.  

Not only that but the coefficients of the curve fit equations used in both the meter and kiln controller induce error.  The species and temperature corrections set these equation coefficients.

For fun, run a simple uncertainty analysis by setting pins in the face of a board and cycle through all the species in the meter, then the temperature corrections, without moving the pins, just changing settings.  Then change the pin placement distance.  If you have a kiln controller with moisture readings you can do the same.  The results my surprise you.

If you check the results against oven dried, then you'll know the uncertainty each setting or pin placement can induce into your measurement accuracy.  

[GeneWengert-WoodDoc]

As DonP pointed out, in drying the deeper you go, until you reach the center, the higher the MC.  So, nails or screws can be used in drying if they are not insulated and are not driven beyond halfway.  

You can use a common shiner nail.  Aluminum or stainless is. Ot required for a single use.  More important is to use a smaller diameter nail rather than a spike...maybe 10 penny nail is best.  Spacing between the nails is the same as the meter pins, usually about 2".

The ost useful depth in drying is about 1/4 of the thickness, as this will give the average MC.

There is some concern that heat will travel down the nail or screw.  However, the temperature gradient when drying is quite small, so this is not an issue.  

Remember to correct for temperature.  The kiln dry-bulb is ok, as 20F makes only a 1% MC difference.  Species correction can be made also, but foreign made meters are often incorrect on species corrections.  Most meters do not have accurate foreign wood corrections.

Because a nail or screw will actually split and compress the wood in order to get in, it is always a better plan to pre-drill the hole at about 90% of the nail's diameter or screw's root diameter(not counting the threads). The hole is to a depth 1/4" less than the expected nail depth...the nail tip goes into I drilled wood for the last 1/4".  Note that the wood shrinks in drying so the hole will tighten as the wood around the hole shrinks.

Remember to withdraw the nail or scores at the end of drying.

Pin meters are not too accurate above 30% MC, but you can get an average MC value over 30% MC by driving the pins 1/8 of the thickness; then calculate the difference between the EMC of the air and the 1/8 reading; then double the difference to get an estimate of the difference between the EMC and the 1/4 depth (or average) reading.  That is, Average MC = EMC + [2x(1/8 reading -EMC)].  Make temperature corrections prior to calculating.  Species corrections are also a good idea, if the meter is calibrated for US species.  Some foreign made meters have bogus species corrections.

[K-Guy]

Some foreign made meters have bogus species corrections

Usually they are calibrated for similar European species ie. White Oak in Europe is a species called Sessile Oak and is not the same as our White Oak.

[D6c]

Here are a few nails I made up with shrink tubing to insulate the shank.  I used some small ring shank flooring nails.  I put a couple of pairs in the slabs at 1/4 and 1/2 depth.

I drilled the hole a little oversize and sealed the top with silicone, but it might be better to drill it a close fit to the tubing and skip sealing it. 
All this all might be an exercise if I got the slide hammer pins for my Delmhorst....assuming you can reuse the holes like mentioned above.



 

[Stephen1]

I often use the same holes on high dollar slabs with the sliding hammer.

I was doing that, drive the pins a little farther each time untill I started getting 7 % giver or take. My buddy and I then had a discussion over some brown pops, decided that the hole's was drying out in the vacuum kiln and I was getting a false reading. 
YH if I the side is the same as the face on A 8/4 or 10/4 slab. The Dr, mentions going in a 1/4 of the thickness, on a 30" slab that would mean the probe has to go in 7".  
I was probing from the sides for a while along with probing the centers, never did get a consisitant reading, so I stopped. I might go back to it , now that I am getting dangerous, I have a little bit of knowledge. 

[YellowHammer]

YH if I the side is the same as the face on A 8/4 or 10/4 slab. The Dr, mentions going in a 1/4 of the thickness, on a 30" slab that would mean the probe has to go in 7".  I might go back to it , now that I am getting dangerous, I have a little bit of knowledge.

No, go in as much as would a true face.  

[customsawyer]

I have tried the hammering in the side and found that if you have thick sap wood you will get a dryer reading then if you drive the pins in some heart wood. This was done on SYP haven't done the experiment on hardwood. 

[Stephen1]

I have tried the hammering in the side and found that if you have thick sap wood you will get a dryer reading then if you drive the pins in some heart wood. This was done on SYP haven't done the experiment on hardwood.

I found that also on the walnut, but that was before I realised about the bacterial pockets in the Walnut. 
I will just keep trying and learning.

[YellowHammer]

It's really a trade off of damage to the wood face and accuracy.  Several snake looking fang holes on the face of a bunch of $400 walnut slabs isn't necessary as long as the operator understands the different relationships on where they are taking readings and how they are taking the readings.  

I will always pin the edges on thick boards still in a kiln because testing the face of the top board will give a dryer reading than the ones in the stack.  Also, it's impossible to face check a bunch of boards in the stack because the faces can not be reached.  So from a practical standpoint the only way to check the moisture of half a dozen thick slab in the middle of the stack is either from the end or the edge.  Also, pin holes in the edge can be hidden by the bark.  

When the moisture drops to lower levels, the resistance of the wood becomes high and constant.  So if I pin an edge and it reads 12% then it's too high for me to bother testing the face.  At that level, the kiln schedule doesn't change and a board with a 12% edge isn't on 7% any face.  

I'm not trying to get an exact number when I'n kiln drying, except at the end.  Rather, I'm trying to determine when the general moisture in a pack of wood, or for that matter, an entire kiln load, requires me to go to the next step in the kiln schedule. 

A moisture meter is just one factor to make that decision.  Just like the amount of water dripping from the condensate and other things.