Problem Drying walnut

[Charles]

I have been drying lumber for a long time and can never figure out why thick walnut gives me such a hard time. I am currently drying 700 bd/ft of 10/4 x 28 x 120" . it was air dried to 16% in the center . I have a Delmhorst 2000 with a slide hammer probe. Kiln Dry bulb was set to 120f and wet to 90
I insert stainless pins into the lumber that reach the center of the slabs at the same spacing as the Delmhorst pins and attach wires to run to outside of the kiln so I can take moisture readings
I can get 1/2% moisture drop per day so second day we are at 15 1/2 MC third day 15% etc. 
But when I get to about 10% everything stops . I watch my wet side and keep the compressor running at 80% of the time. The MC inside the kiln is about 22% . What I have done is raise the dry at 5 deg. increments over a few days with the compressor shut off and will get a .75 MC drop in the slabs per day. Doesn't make sense but thick walnut is the only lumber I do this to. 
Anybody else 

[Southside]

I have some to do that is at 15% right now, 8/4 so I am interested to hear what the recommendations are.  

[YellowHammer]

Thick walnut stalls. When it does, I will run the kiln temp to 150 and hold it for a couple days, then vent the moist air as it cools then hit it again with the compressor.  Most times it will go down then.  

[Southside]

No chickens?  :D

[xlogger]

I have been drying lumber for a long time and can never figure out why thick walnut gives me such a hard time. I am currently drying 700 bd/ft of 10/4 x 28 x 120" . it was air dried to 16% in the center . I have a Delmhorst 2000 with a slide hammer probe. Kiln Dry bulb was set to 120f and wet to 90
I insert stainless pins into the lumber that reach the center of the slabs at the same spacing as the Delmhorst pins and attach wires to run to outside of the kiln so I can take moisture readings
I can get 1/2% moisture drop per day so second day we are at 15 1/2 MC third day 15% etc.
But when I get to about 10% everything stops . I watch my wet side and keep the compressor running at 80% of the time. The MC inside the kiln is about 22% . What I have done is raise the dry at 5 deg. increments over a few days with the compressor shut off and will get a .75 MC drop in the slabs per day. Doesn't make sense but thick walnut is the only lumber I do this to.
Anybody else

Charles, I'd like to know more on how you do your pins and wiring, maybe pictures if possible. I have look at the Kil-Mor on Delmhorst  site and would not like paying that. Also on the meter what temp do you use, inside wood temp or outside air, I would think inside but not sure.
thanks for help, ricky

[K-Guy]

Thanks for answering for me Yellowhammer.

Southside

Sacrificial animals are only a last resort. I recommend buzzards. :D

[tule peak timber]

K-Guy, Fowl remarks aside,,,,,,I have been finishing off loads at 155 with the vents open for a week to remove that last bit of moisture.Should I follow another method ?

[K-Guy]

@tule peak timber 

If it's working, I'm not going to say it's wrong but you may want to follow the schedule till it locks up and stops drying. Then put your heat to 140° till the moisture starts to move again, at that point cool the kiln down to 120° and finsh the load. It might be more efficient and quicker.

[tule peak timber]

Thanks.  Rob

[YellowHammer]

No chickens?  :D

There are always chickens.  It just depends on how they are being utilized.    Sometimes I prefer them fried.  :D
Other times,....well, ask Jake about that.   :D :D

[scsmith42]

@tule peak timber

If it's working, I'm not going to say it's wrong but you may want to follow the schedule till it locks up and stops drying. Then put your heat to 140° till the moisture starts to move again, at that point cool the kiln down to 120° and finsh the load. It might be more efficient and quicker.

Stan's recommendation is what I've done successfully in the past.

[GeneWengert-WoodDoc]

From DRYING HARDWOOD LUMBER, page 102.  
What To Do When Drying Apparently Stops
What can be done when drying seems to stop in the middle of the kiln run? Drying will never actually stop if the EMC of the kiln atmosphere is lower than the core MC of the lumber, but the drying rate is extremely slow. To correct this problem of "slow drying," the dry-bulb temperature can be slightly increased (perhaps 5°F (2°C)) during the intermediate stages of drying. Higher increases are not recommended because of the risk of degrade. If a kiln operator decides to increase temperature above 30% MC, the operator should make sure that the kiln controller is properly calibrated.

[YellowHammer]

It's rare for me to dry any walnut completely without having to give it the double hit.  Even on 4/4 I've discovered wet spots in spots in boards where the rest of the load was dried.  So even individual pockets can stall when the average of the board won't.  Of course, incomplete drying causes all kinds of quality issues down the road, so whenever I'm drying walnut, I'll stop at an average of 8%, go into a sterilize cycle, and where most wood will continue down to my target 7% on the sterilization cool down and rest cycle, it's not unusual for walnut to actually rebound upward, generally a percent or so.  I assume that's the stalled areas releasing their moisture, so I do the double hit and it will come down nicely and evenly the second time around.  So I plan for an extra three days cycle time on any walnut, whatever the thickness.  I've got 3,200 bdft in the Nyle right now that is misbehaving as expected and undergoing that exact process.  With walnut, no big deal, that's just what it likes to do.  With all the issues buying, sawing, stacking, trimming and dressing walnut, it's one of the most aggravating and high load species to process correctly, and I wouldn't do it except it people buy it as fast as I can produce it. 

[GeneWengert-WoodDoc]

We do indeed see this "high MC and no drying" situation especially with walnut, as YH indicates.  Much of the time, it is due to the bacteria that get into the stem of the tree- - a topic we have covered before.  Heat and patience will help eliminate this issue.  If you think it is bad with American walnut, you should see how bad it is with tropical walnut...we had some 8/4 that air dried a year and kiln dried for a month and the core was still around 45% MC.

If we apply too much heat too early (the MC is too high in the core), then we will see fine hairline checks (you might also call them honeycomb) in the wet core regions, so a small amount of heat is better than a big jump in temperature.

Note that two coats of Anchorseal end coating are critical to prevent end honeycomb.

[tule peak timber]

I've been up since 3 reading about drying walnut. I need to make some changes.....

[Charles]

Walnut is out and this is what I did to get it to move in moisture
I was bumping the temp up 5 degrees at a time till I got to 130f the compressor had little effect on lowering the MC  I had the compressor on for 8 hrs then off for 8 MC moved more with the compressor off. Once I got to 130f with the compressor off I started to see better movement, I left it for a day with  the compressor off and moved to 135f and again seen acceptable movement, then to 140 and by that time I was reading between 7 & 9 % mc MC inside the kiln was 18% (very low) When the lumber had cooled after opening the kiln my final reading was between 7.2 & 8.7 at the center of the lumber and no water pockets 8)
So next time i'm gonna do what yellow hammer does and go straight to 150 then cool to 120 hit the compressor again. I think that my be a little quicker than my way

As far as the pins go I push my meter into the lumber to get a couple of small holes then hammer in very fine stainless finishing nails (the smallest I can find) so they reach the center of the lumber, I put a small plastic washer over each nail and attache an alligator clip to each nail that is soldered on to number 18 wire. these wires then reach outside the kiln when the door is shut. I have them in order from top to bottom recorded on a sheet so when I check them I can tell if everything is drying the same. I have a remote thermostat to record inside temp of the kiln and I use that to set my meter 
thanks for all the response and glad to see it wasn't just me

[YellowHammer]

Each wood species has its own personality.  Walnut is just cranky.  

[xlogger]

Thanks Charles I might try that. I'm going to put some walnut in solar kiln today 8/4 slabs. I got this logs a few weeks ago and they have been cut for about two years and I just cut them up a week ago. I didn't even check the MC, maybe after a couple months with hot weather coming now I'll check and see if they are ready for the Nyle.

[xlogger]

I guess I should of ask a question on my last reply. Wondering on those who have solar kiln and use them to put walnut in find it works better than air drying before putting in DH Kilns?

[Stephen1]

As a new kiln operator , I think I will follow along. 
I have 8/4 and 12/4 walnut 36" in the V kiln now. After 9 days it is still dumping a lot of water each day. 
I am going to open this afternoon and check moisture as I have another 1000 bd ft coming tomorrow. It might have to wait a bit. 

[tule peak timber]

As a new kiln operator , I think I will follow along.
I have 8/4 and 12/4 walnut 36" in the V kiln now. After 9 days it is still dumping a lot of water each day.
I am going to open this afternoon and check moisture as I have another 1000 bd ft coming tomorrow. It might have to wait a bit.

I for one will be most interested in your experience with the thick walnut.

[Charles]

Thanks for all the answers guys. They have been a great help for me

[Stephen1]

The new load of walnut  arrived 1500 bd ft of live edge, 1" all the way up to 3".
I pulled a load of walnut 2" and 3" and Elm out of the kiln. 
I checked the moisture and tried to compensate for the temperature of the wood. I had readings of 10.1% all the way to 39%
I let the wood cool over night. I had readings of 9% - 19% 
I used the hammer probe for the 1st time. 
What does everyone do about the probe holes in the wood? will they close up? Do you use the same holes each time? Do you use new holes? 

[WDH]

Delmhorst told me that you can use the same holes for subsequent measurements. 

[GeneWengert-WoodDoc]

Oftentimes you can go into the lumber from the side and not the face.  This eliminates holes. 

 The old holes often have surface drying and should not be used.  Also, the depth is 1/4 of the thickness.