1st time drying white oak in the L53 kiln

[blackhawk]

This is my first time drying white oak in my Nyle L53 kiln.  It is all 10/4 thick slabs, 26-30" wide and 10' long.  I am getting steady drying but it is slow.  It has been slower than 10/4 walnut slabs that I dried a few months ago.  I am at 122° and 22%RH in the kiln, so my kiln environment is setting around 4.2% EMC.  I am only getting 0.3 to 0.4 drop in EMC per day.  I have a wind meter and I am getting good flow through the stack.  My compressor never kicks on because the kiln air has stayed dry over the past 10 days.  I've actually had to throw some water on the floor to keep the humidity up a few times. 

Is the 0.3 to 0.4% EMC normal for 10/4 white oak?  I attached a graph of my actual moisture content of the lumber.  I have seven Lignomat PK probes in my lumber in different areas that I read with my meter daily.

[doc henderson]

I do not have a kiln, but oak goes slow and the thicker the wood, the slower.  if you are making steady progress that sounds good.  If you push too hard, you may get more degrade.  at the MC you are at, surface moisture and therefor airflow becomes less important.  what is your target MC.

[doc henderson]

Looking at your graph, you have, and continue to make steady progress.  Your individual probes follow there own path.  this may be the actual MC in that spot or other wood characteristics at those probe areas.  the lines are all parallel.  The highest and lowest lines remain the same and the spread remains about 7%.  so, the different areas the probes are in are at different MCs but drying at the same rate.  If these probes are all in different boards, you could double check the dryer boards with a pin less meter, and poss. remove them early.  If you make the kiln less aggressive with a higher EMC, it will take longer, but the wetter wood could catch up without over drying the lower MC boards.  How many bord feet are in the kiln?  the thicker wood has farther for the core moisture to go.  Are you in possession of a schedule for this thickness of white oak?  I have no experience but am a vigorous student of this art! 

[doc henderson]

at the current rate, it may take 30 days to dry the 19% to 7% if it continues to dry at the same rate.  it may slow as it gets drier.  I would double check the wood with a pin less. but your probes appear to be very consistent.  Are the pins in wood that represents the whole board?  not in a knot or denser area?

[doc henderson]

@GeneWengert-WoodDoc @YellowHammer @customsawyer @K-Guy 

[doc henderson]

so, the scale in the Nyle L53 manual show 4/4 WO at 2.5% MC loss per day.  for 6/4 and 8/4 there is a multiple of 0.6 and 0,4 respectively.  that puts 8/4 at 1% MC loss per day.  I did not see an estimate for 10/4 but it might be 0.2 and that would be 0.5% MC.  I doubt the multiple continues at the same increment because that would make 12/4 have a multiple of 0.  so, 4/4 dries at a max of 2.5%/day.  6/4 dries at 1.5%/day.  8/4 dries at 1%/day.  I think your rate of 0.4 is safe and steady.  I would continue as you are but may take some time.  If you have more than 1000 BF, that could further slow things.  How much water is pulling from the wood per day?  in that case if one of one or two of the slabs are at your EMC say of 7%, you could pull those and finish the rest at a faster rate.

[doc henderson]

I texted Doc Wengert.  he is doing well, getting chemo.  He continues writing articles monthly.  he sent me some info I will try to post here. 

[blackhawk]

I am running the T3-C1 kiln schedule adjusted for my DH kiln from the USDA Hardwood Drying manual.  I want to get the slabs down below 10%.  I have probably about 500 bf in the kiln.

[doc henderson]

I hope others with more experience will chime in.  you are making good progress, maybe just slower than you want.  to reach 10% should be about 7.5 days for the wettest wood, and 4 of the probes are under 10%, I think.  If the compressor is not on, you could bump the temp a bit.  it does not look stalled.  are the 7 probes in 7 different boards?  If so, you could consider taking out the dry wood.  Do you have this sold or do you know what it will be used for?  Thanks.

[doc henderson]

at 600 bf, looks like you have about 10 to 14 slabs in the kiln depending on if you consider 2.5 inches to be 2 or 3 bf per square foot.  

[YellowHammer]

10/4 white oak is TOUCHY!  I just took a load out of 9/4 and I treated it with kid gloves for the whole process, and still face checked a few boards.  White oak is extremely easy to honeycomb (you are adding moisture from what I read, so be careful) and even easier to face check.  If you push it, you will ruin it, unless you like cracked wood.  I would consider 0.5.% per day OK, but even that is a little fast for my taste, but I am concerned with the wide MC spread on your graph, I would be worried about surface checking on some of the boards, just from that. 

In additional, keep your temps down, but I think you are already beyond that point, because slightly higher temps will significantly weaken the wood and will lead the checks.  Don't forget white oak is waterproof, so that same structure makes it slow to dry. 

Thick white oak, air dried, is sure to surface check, as even the rate of air drying, here in Alabama, will cause it to exceed its allowable moisture removal rate.  With a kiln and thick white oak, the idea is to slow the drying down, even more than air drying, and control it.

[blackhawk]

Yellowhammer - I have only been averaging about 0.3-0.4% loss per day.  I am at 122°F now.  Should I be cooler than that?

Can you elaborate more on being careful about adding moisture?  I have been doing that to keep the EMC environment in the kiln at least 4%.  When the driest boards hit 6%, I planned to raise the EMC in the kiln to 6% so nothing gets drier than that.  All of these slabs came out of the same log and were air dried in the same stack. I have been perplexed why those two in my graph are so much higher.  I kept my probes away from knots.  I guess that I must have just hit a wet pocket in those two or they could have been from the bottom of my air dry stack.  They may not have air dried as much being closer to the ground even though I keep my stacks 10" off the ground.

[doc henderson]

It seems you are doing pretty well.

[scsmith42]

You're doing fine.  It's important to take your time with thick WO.  Do you have both shell and core probes installed?  If so, what is the delta between them?

When my RH% drops too low in the kiln, I'll turn on my fogging system to keep the RH% around 35-40%.  This will slow the drying rate a bit but will help narrow the delta between core and shell MC%.

I just finished up a load of 16/4 red oak last week.  Came out fine.

[customsawyer]

I don't dry much oak, so will step aside and let YH and SCS lead you. Maybe Stan will chime in here in a bit.

[YellowHammer]

Adding too much moisture, too quick, to the kiln atmosphere or the surface of the boards, will in some cases wet the outer fibers of the case enough to make it swell and since the core is in the process of drying and shrinking, then the swelling case will literally pull the core apart, and crack from the inside and they may not even be visible form the outside of the board.  That's called honeycomb, although it doesn't look like honeycomb.  Take a piece of thick foam board and just pull it apart, that's what these failures look like.  Some species are more prevalent than others to do this, and in my experience, white oak, basswood, persimmon, and sassafras to name a few, and generally it happens in only the thicker sizes, and especially if the board width get over 8 or 9 inches wide, because the stress has no where to relieve itself, so the inner fibers of the board fail.

If you take a chop saw to an otherwise unblemished piece of thick stock and you have internal cracks that look like tearing and ripping, then that's honeycomb.  It's also a real good way to get a bad reputation with customers, selling thick stock that looks good on the outside and then they take it home and hit it with a saw and it's blown apart inside.  We get many of our competitors customers that way.

I would advise to not dry anything to 6%, there is a Yellowhammersim that says "Once the cookies are burned, they are burned and you can't do anything about it" which means once you get wood too dry, simply raising the MC won't fix it.  I personally dry to 8%, then sterilize to 150F for 24 hours, and that will equalize and bring the final moisture content to a dead on 7%.  Once you get to 6% bad things start to happen, boards will deform more and machinability goes down.  So you will need to adjust your WB/DB to asymptote to that level, which will let the other boards catch up and so will also reduce your spread.  That's one treason your spread is so large, your depression steps are too drastic and too far apart.  Increasing resolution on both will help prevent that.  Also, we are talking about 1% moisture levels so you have to be able to measure them accurately, which you see to be able to do.  As I mentioned, drying thick white oak is not easy, but since it doesn't really sticker stain deeply, that constraint can be ignored for the most part.

[blackhawk]

You're doing fine.  It's important to take your time with thick WO.  Do you have both shell and core probes installed?  If so, what is the delta between them?

I have one pair on the same board as core and shell.  It is reading 9.4% on the shell and 12.8% in the core.  10/4 thickness.

[blackhawk]

That's one treason your spread is so large, your depression steps are too drastic and too far apart.  Increasing resolution on both will help prevent that.  

By depression steps, are you talking about the steps in the T3-C1 kiln schedule that I am using?  What do you mean by increasing resolution?

[doc henderson]

I think he is talking about the RH being so low (wet bulb depression), and resolution means bringing all the lines closer together and near the same MC.  I bet things will turn out fine.  Thanks for the ride.

[scsmith42]

Good advice from Robert above about sterilizing at around 8%.  With thick slabs, I usually start it around 9%-10% because I usually add an extra day to the sterilization cycle  in order to ensure complete penetration  (with thick slabs that is).  

Seriously, you'd doing fine.  A 3% delta between core and shell on thick oak is about right.  .3% MC loss per day is also about right.   The variances across your load are a little bit unusual but some variance is normal.

I'd keep it at 120F and stick with the .3 per day MC% loss.  You may need to add some RH% now to slow down the faster drying wood a bit and let the higher MC% lumber catch up.

[blackhawk]

Good advice from Robert above about sterilizing at around 8%.  With thick slabs, I usually start it around 9%-10% because I usually add an extra day to the sterilization cycle  in order to ensure complete penetration  (with thick slabs that is). 

Seriously, you'd doing fine.  A 3% delta between core and shell on thick oak is about right.  .3% MC loss per day is also about right.  The variances across your load are a little bit unusual but some variance is normal.

I'd keep it at 120F and stick with the .3 per day MC% loss.  You may need to add some RH% now to slow down the faster drying wood a bit and let the higher MC% lumber catch up.

Scott - Thanks for the help.  I have been slowly increasing the relative humidity in the kiln to get the kiln EMC back up to 8%.  I didn't want to shock it. I have a homemade mist system that is controlled from the L53 that does pretty well.  I'll just need to be patient and let all the slabs equalize.  This white oak is tougher to dry than walnut.