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Kiln drying after air drying

Started by SDM, July 11, 2007, 04:57:44 PM

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SDM

can air dried lumber be later kiln dried....any time limits , problems etc?

thanks, Shawn

jim king

Shawn:  The more you air dry or pre dry the better results you will have in the kiln and less degrade.

If you got the time sticker and air dry everything to 20% or less.  (My experience)

Dodgy Loner

Welcome to the forum, Shawn.  Like jim says, not only can you kiln-dry after air-drying, it's often preferable to kiln-drying only.  Personally, I air-dry everthing, because I don't own a kiln.  The important thing is to bring the wood down to the equilibrium moisture content, regardless of how you go about it.
"There is hardly anything in the world that some man cannot make a little worse and sell a little cheaper, and the people who consider price only are this man's lawful prey." -John Ruskin

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alsayyed

Hello fallas it is very interesting topic. Are you people telling me or should some one explain this to me. If I have placed wood under the shade and no matter how much wind is blowing  through or is circulating between the wood slabs will be perfect for drying or removing the MC%.
Because from my experience I have placed some wood under the shade and know it is almost two months and still have 12-15 MC. How long dose it takes when slabs exposed to the air drying influence.

DanG

Alsayyed, the general rule of thumb for air drying hardwoods is about one year per inch of thickness.  For most softwoods, it is much shorter.  In any case, if you achieved 12 to 15% in two months, you've done very well.  I would expect shorter drying times in your climate. :)   Your wood may be as dry as it is going to get without a kiln.
"I don't feel like an old man.  I feel like a young man who has something wrong with him."  Dick Cavett
"Beat not thy sword into a plowshare, rather beat the sword of thine enemy into a plowshare."

alsayyed

DangG thank you for replying so i am lucky. sometimes here in Qatar very hot air is blowing so when it blows this the reason why the wood dried quck. even sometimes I have got 8-9 MC so I should be happy and what I am doing is correct. thanks again for your clarification very nice

Tom

Be sure to take your moisture readings from the center of the timber.  It takes a long time for the moisture to reach the outside.  Readings from the outside surfaces will be inaccurate relative to the entire piece.

alsayyed

Quote from: Tom on July 12, 2007, 10:51:35 AM
Be sure to take your moisture readings from the center of the timber. 
this is a new information to me Tom thank you. My meter dose not go deep like if i have 2 inch it will not give exact reading. but if it is 3/4 i will give good reading. My meter is called Delmhorst instrument, it has to small pins which is about 1/2 in length.

Tom

that is a good meter.

When you reach the final phases of drying, you can cut a board in two(or cut the end off) and measure the center if you need to justify your moisture content.


WDH

Some species do not air dry without a lot of degrade because of the uncontrolled conditions in air drying.  Also, some white woods like maple, hackberry, etc. can quickly develop a gray oxidation stain that penetrates the wood and turns it a grayish color.  These woods do better if they are put in the kiln immediately after sawing.  Because the variables in air drying are very difficult to control, air drying is more succeptible to drying degrade than if immediately kiln dried.  Some species like oak are persnickety, and take a long time to dry correctly in a kiln.  These slow drying/difficult to dry species sometimes benefit from pre-air drying to an extent on stickers before going into the kiln.

Some of this might not be right, but it is what I have gleaned from research and reading.  I do not have a kiln, so I am sentenced to air drying with all the inherent uncontrolled variables.  Fortunately I have had pretty good luck with air drying.  I have some soft maple air drying on stickers since December, and I am eager to see how it turned out.  Currently, the moisture meter reads 12 - 15%.  I have not sampled the interior of the stack yet (important to do as I have learned from the hard school of drying knocks ::)).
Woodmizer LT40HDD35, John Deere 2155, Kubota M5-111, Kubota L2501, Nyle L53 Dehumidification Kiln, and a passion for all things with leafs, twigs, and bark.  hamsleyhardwood.com

scsmith42

Alsayyed - Delmhorst makes great meters.  You can order longer pins for yours from them (such as 1" pins).  Most people get the insulated pins.

SDM - Ditto WDH's comments. 

re Air drying then kiln drying, yes this is commonly done, but for economic rather than quality reasons.

What I have been told by the folks at Nyle (and Dr. Wengert) is that with 4/4 to 8/4 lumber, you will have the highest quality and least degrade losses if you log and end seal on day 1, mill on day 2, and get into the kiln on day 3.  Anything beyond this will increase degrade.

From my own experiences, the best results that I've seen are when the lumber goes from log to kiln as quickly as possible.  I think that this is because I can closely regulate the drying process from green to 25% MC, which is where the bulk of degrade is caused.  I use a low temperature Dehumidification Kiln.  When I KD lumber that was air dried first, I see a lot more wet pockets and it does not seem to dry as consistently as lumber that entered the kiln very green.  Getting a good end sealer on your logs as quickly after logging also helps reduce degrade.

Hope this helps.

Scott
Peterson 10" WPF with 65' of track
Smith - Gallagher dedicated slabber
Tom's 3638D Baker band mill
and a mix of log handling heavy equipment.

alsayyed

Quote from: scsmith42 on July 12, 2007, 10:22:22 PM
Alsayyed -  Hope this helps.

Scott
Off course this is helping too much. with this forum every bit of information is very helpfull to me and to the other newly joint.
i thank everybody and I appreciate your knowledge.

alsayyed

Don_Lewis

I do disagree with the statement that you should ALWAYS air dry first for best quality. There have been a lot of studies proving that  some species such as the Oaks, give much lower yeilds if air diried first. Also some species, such as Hard Maple should never be air dried except in cold weather. But many people do air dry and then kiln dry. In most cases it is a necessity but generally you will lose more to degrade than you save in energy costs.

Also, the best pin meters to use with a kiln are ones with insulated pins and you push them 1/3 of the thickness, not halfway. Uninsulated pins are for shop work and not good for kiln drying operations.

glalonde

What is a good sealer for log ends before KD?

scsmith42

Most folks use Anchor Seal.  You can buy it from Baileys.

Scott
Peterson 10" WPF with 65' of track
Smith - Gallagher dedicated slabber
Tom's 3638D Baker band mill
and a mix of log handling heavy equipment.

Tom


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