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Thread: Looking for more advice on kiln drying...

  1. #1

    Looking for more advice on kiln drying...

    Hey gang....

    I milled about 2000 BF of lumber over the weekend.

    Ash, elm, cherry, birch, beech, and maple. Heavy on the maple.
    It's all on stickers now.
    I've got 2 kilns available to me, locally....and only these 2.

    Kiln #1 wants me to air dry it for 2 or 3 months, then he'll take it. He charges 30 cents/BF. He has a DH kiln.

    Kiln #2 wants it to air dry for 5 months, then he'll take it. He charges 16 cents/BF. He's Amish, and heats the kiln with wood.

    Both take it to 6%

    I want to go with kiln #2, but I'm being given some advice elsewhere that leaving maple on sticks that long will degrade it. I'm being told to find some other kiln operator that will dry my wood from green, or from a high moisture content, since these woods dry easily from green.

    Thoughts?

  2. #2
    Join Date
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    Allow the lumber to air dry for at least 3-4 months prior to kiln drying(variables here: where you are located(high humidity area), how much air flow has access to the lumber and also how much moisture has access to it).

    I allow all my lumber(that is kiln dried) to air dry for the period stated. This allows as much moisture to evaporate, so that you don't "shock"(case hardening(dry on the outside..wet on the inside) the lumber when you place it in the kiln to wet. You can never be to safe here...if you canbe patient, give it a few extra months.

  3. #3
    Join Date
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    were the stickers dry or green ?

    folks up here also heat kilns with wood and seem to do a fine job. most want to have the stock air dried for a few months to lower the total amount of water driven off. But I am not a kiln expert. I would say go with #2 unless you are in a big hurry. BTW what did he say about quick drying and the chance of degrading the lumber?
    lou

  4. #4
    The stickers were all kiln dried.

    One person told me: "The maple and white ash will produce the best color being dried from green and greatly reduce the chance of gray/sticker stain."



    This may be true, but neither kiln will take my stock green.

    Dr. Wengert from Woodweb writes me:
    "I vote for neither kiln and would look for someone that would take it at a high MC...high MC propobably means that they have a kiln with enough heat and venting and spray. Note that if you air dry first, you will likely not have any drying stress (casehardening), so the kiln will not have to use a conditioning (steaming) period. When drying green, casehardening is likely and so conditioning is required to remove it."


    As I only have these 2 kilns as options....I hope air drying maple for that many months won't leave me with junk.

  5. #5
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    [QUOTE=Dee Dee Martin]The stickers were all kiln dried.

    One person told me: [font=arial][size=2][color=#000000]"The maple and white ash will produce the best color being dried from green and greatly reduce the chance of gray/sticker stain."


    In general, it is not wise to cut any whiteish colored wood when the humidity level is high. This can produce a grayish over tone to the surface of the wood(this gray color is a mold). Stickers being wet can causes this where the stickers cross. Most of the time these stains will not come out completly.

    If the lumber is exposed to higher humidity levels, you could have a problem with discoloration. If not exposed to high levels of humidity, you should be fine(meaning...if you store in a clean basement or garage with descent air flow).

    I would not have any of my lumber...even low grade material...placed directly in any kiln without air drying. Cherry and walnut that I own rarely see a kiln...all maples, oaks, ash and poplar will go to the kiln.

  6. #6
    Have you considered building a kiln yourself? I built one about 5 years ago, at my last house that was solar powered, and only required 2 fans placed in it. they were on timers. The overall size wasn't too big, and it would dry 600 BF of cherry in about 45 days in the summer and 65- 70 days in the winter. I don't think I spent $400 total on the whole project including paint, and plexiglass for the roof. In the summer time it would hit temps of 180+. Worked very well at drying and killing the insects.
    "When we build, let us think that we build forever." - Ruskin

  7. #7
    Join Date
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    As stated by Donnie and others, air dry first.

    I would be concerned about drying mixed woods in the same lift (stack of wood.) There is no way to control the drying levels. softer and porus woods such as cherry and red oak will dry at a faster rate than tight grain woods such as maple, birch and beech. Either one species doesn't reach the 6% level or the other is too dry and moves all over the place once used in projects.

    Another question is how do they control rate of moisture loss. The kiln has to be ramped up in temp so the moisture loss is limited. Too fast a loss in the beginning will result in unstable boards. Thus I would run from any operator that leaves the kiln at a constant temp and moves lifts in and out as they dry. NOTE" this is acceptable for dimension lumber as it is only dried to 12-14%.

    Weight on the top of the lifts? Many attempt not to do this as it reduces the height room in the kiln. But, the cost is that the top 4-5 rows of boards will bend and twist in the kiln.

    Proper sticking is a must. If stickers are not at 1-1/2 ft intervals placed EXACTLY on top of each other the boards will dry wavy as the weight of the wood and stickers above will cause the boards to bend and dry as bent wood.

  8. #8
    Guys,

    No room to build a kiln.

    I said nothing about weight on the lumber, in the kiln. Only while air drying, which I understand to be appropriate.

    Stickers are properly placed.

    Donnie, thanks for the input. Good responses.

    The stack is 90% maple. My kiln operators have years of experience, and many happy customers. I suspect they know what they are doing.

    Thomas, you say "too dry". If my maple gets dried to 6% in the kiln, my cherry that's mixed in, will go even lower. I never knew that could be a problem....

  9. #9
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    I have heard that diffrent species of wood will dry at varying rates...and it makes sense we you consider the make up of the diffrent woods species. However, that has not been my experience when air drying lumber. I have stacked diffrent species together and found that they acclimated equally. To this I can not explain why, frankly.

    As far as putting weight on top....don't worry about it. If the boards are stacked properly you need not concern yourself with this. Think about it...if a board is going to twist/cup or whatever...it's going to do it....no matter what you put on top. It may not do it while it dried out, but whatever tension has built up will eventually release.

  10. #10
    Donnie, I'm not so sure that's true.

    I've seen lumber that's air dried with no weight on top, and the top layers end up quite the twisted mess. Lumber dried with a great deal of weight on top, come out much better....and remain so, all the way thru manufacturing.

    No?

  11. #11
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    Quote Originally Posted by Dee Dee Martin
    Donnie, I'm not so sure that's true.

    I've seen lumber that's air dried with no weight on top, and the top layers end up quite the twisted mess. Lumber dried with a great deal of weight on top, come out much better....and remain so, all the way thru manufacturing.

    No?
    It has been my experience that weight is not needed. True, the fibers of the wood will shrink as it dries(obviously). However, what cause boards to tweak wildly is built in tension...either relased when the log was cut or that has become more pronounced as it dried. If the board wants to move...it will...no matter what.

  12. #12
    De De,


    There are two types of moisture in wood. kiln drying takes out the moisture that is trapped in the cells of the wood. The free moisture is why you air dry before placing in the kiln, most freshly cut wood is somewhere around 26-30% moisture contenet. To place it in a kiln at this time would remove the moisture too fast and degrade the wood. Air drying allows this moisture to be removed and at night gives the wood drying a break and actually adds a small amount of moisture back into the wood allowing it to relax a little. Solar kilns as mentioned do somwhat the same thing. It acts like a kiln during the day and gives the wood a little "breather" at night. For some really good articles about solar kilns you may wnat to visit www.theoak.com where there are a couple articles about it. Also, different woods dry at different rates with oak being the hardest to kiln dry without degrading. They are a lot of charts detailing this on the net.

  13. #13
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    Dee Dee,

    I've been following the conversation on WW but didn't throw my two cents in over there. Wengert knows his stuff but he has a hard time relating to small operations. He thinks in terms of huge stacks going into huge kilns and can't really relate to situations outside of that world. Small scale operators just can't afford steam stress relief systems for their kilns!

    I own a small sawmill/lumber operation. I air dry (shed dry, actually) my lumber before using a DH to finish off. As mentioned, I try not to cut light colored woods in the heat of the summer, but when I have to, I re-stack the pile about two weeks later making sure the stickers are not aligned in the same spot again. This really cuts down sticker stain, and I haven't experience a noticable loss of brightness as Dr. W. warned you of.

    In my opinion, you're faced with a time vs. money option. If you want the lumber quickly, go with option one. I think his price is very fair.

    If you don't need the lumber soon, the Amish kiln is the better value. Actually, it's a steal. Personally, I admire the Amish for their hard work ethic, but I am not a big fan of their quality. I also have a hard time with their rate structures, which is a deal for consumers but a pain as a competitor, but this is just sour grapes talking here.

    As an aside, does anyone know how the Amish get air circulation in their kilns if they can't use electric fans?

    As far as weight, I have had a few unweighted stacks dry fairly well, and a few weighted stacks that still moved, but on the whole, the more weight, the better the odds of flat lumber.
    Last edited by Brad Smith; 07-27-2005 at 5:18 PM.

  14. #14
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    Yes different woods dry at different rates.

    If you are air drying this isn't critical, some Cedar will be dry in 6 weeks, some oak may take 6 months. But after 6 months your mixed stack is all air dried. Just meant your cedar sat in the stack doing nothing for 4 months.

    In a kiln however different schedules are used for different woods, drying something like oak too fast will cause checking or case hardening. While pine is almost impossible to dry too fast. Mixing woods means you can only dry at the slowest schedule and you run the risk of overdrying the faster drying woods.

    Air drying then finishing in a kiln is a valid drying method for many species of wood, and is even prefered for some. On the plus side the wood spends less time in the kiln = lower kiln cost. Kiln operation is less critical than at the beginning of the drying cycle where most problems are caused. Taking the wood from 15% mc to 8% mc is relatively simple. Downside is.. it takes 2-6 months of air drying time, and some species are more dificult to air dry than others. So long as you can successfully air dry the maple without much degrade, then taking it to a kiln to finish drying is a good option. Most of the degrade will occur in the first few weeks. Mould / Stain if it dries to slow, checking if it dries to fast. Once the outside of the wood gets down to 20% mc then the wood is pretty safe in a stack (unless bugs decide to eat it )

    Both option should work,
    Option 1 will get your wood dry faster.
    option 2 is cheaper because your wood will be dryer = less kiln time ( plus the guy is Amish )
    Kilning from green is good if it's done properly, but takes longer in the kiln as the initial drying must be slow and the conditions controlled more precisely than the later stages. If the local kiln guys are achieving good results it's hard to fault how they are operating.

    Weight on the stack? Often it's not needed, but you can reduce warp and cupping by putting a LOT of weight on to of the stack. I think the recommended amount is about 4" of solid concrete I try and plan my air drying stacks so the unstable wood is on the bottom, and top it with more stable material. It does help.

    Cheers

    Ian

  15. #15
    Join Date
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    Amish drying

    Hi Brad,
    Been a while since I was ove at your mill(I think your mill).
    There is an Amish kiln setup over by Perry. They use convection to move the air. The top of their kilns are completely vented. The one there has the wood stacked on beams about 3-4 ft above the floor. the warm air is piped in just below the beams. It then rises through the stickered wood and out vents at the top. They use baffles to force the heated air through the spaces left by the stickers. They let the stove burn down overnight to "Relax the wood."or as Jacob puts it-I need to get some sleep.

    Kinda neat operation as much of the stovewood is the slashing, limbs, large knots they cutout and other waste products from the mill. They let the stove burn down over night to "relax the wood."This is what reduces the energy cost to nill. The one near Belfast uses kid power to cust and split large limbs wolf trees and the like as they dry for other sawyers.

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