Replies

1. 
   forestgirl | Apr 24, 2003 06:52pm | #1

   Here's a link to get you started (there's a publications list at the end with further resources):

   http://www.ianr.unl.edu/pubs/forestry/g60.htm

   The most recent magazine I remember having a kiln article was American Woodworker, it's in issue 94.

   forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl   ;-)

   
   

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   Edited 4/24/2003 11:56:41 AM ET by forestgirl

2. 
   StanleyNiemiec | Apr 24, 2003 07:34pm | #2

   You don't necessarily need heat to dry lumber.  A dehumidifier can also be used as in the drying process heat is used to establish kiln relative humidity conditions.  At a 70 degree (F) temperature, if the relative humidity of the chamber is 48%, the wood will equilibrate to 8.8% MC. 

   Where heat is beneficial is relative to sterilization especially as related to powderpost beetle.  For 4/4 stock, sterilization is accomplished if the lumber is maintained at a temperature of 125 degrees (F) for a period of 46 hours at RH conditions of 61% (9.7% EMC).

   The expense of a kiln is generally associated with satisfactory instrumentation that will be accurate enough to control both temperature and relative humidity, and making sure that there is sufficient air circulation within the stack (good fans and baffles).

3. 
   JohnWW | Apr 25, 2003 01:18am | #3

   I'm reading between the lines here, but I think the problems that have cropped up in the work already done are due to not designing the pieces to expand and contract with seasonal changes in the relative humidity of the air.  Drying your wood in a kiln whether at home or in a commercial unit won't solve your fundamental problem. 

   Drying the wood out to a low moisture content in a kiln won't prevent the finished piece from reabsorbing moisture during a damp spring and summer that I'm guessing is common in Ireland.  By midsummer the wood will probably be back up around 10 or 12%, when the heat goes on in the winter the furniture will again dry out down to under 5%.  This will go on forever, wood will never stabilize, no matter how it was dried before it was made into furniture.  Finishes that seal the wood will slow the process down but no finish will prevent the wood from changing with the seasons.  In the environment you are in you must design and build your pieces to move with the seasons without self destructing.

   Hope this helps, John

     

1. 
   rwobee | Apr 25, 2003 01:45am | #4

   John, you are certainly correct about designing the work to allow for seasonal movement; the pieces I referred to were done before I got involved in the project. To be more specific, I am going back to Ireland for more work soon, and I know the wood has been stored without a thought to its workability when I arrive. So, I'm trying to figure out a way to at least bring the MC down to the point where its roughly in the middle of the swings the climate in Ireland will throw at it. I think 8-9%, maybe abit lower, as the weather there is typically more cold, with heating systems going for 8 months of the year. I'm hoping for a simple kiln that can be assembled by the people already there so the wood is ready to use when I arrive. It's tough to get anything in a hurry over there, which is why a simple design using commonly available parts is important. Any ideas?

   Thanks for the reply, Russ

1. 
   StanleyNiemiec | Apr 25, 2003 02:10am | #5

   If the wood currently has a MC of 16-18%, you should be able to establish a kiln schedule and dry it to 8-10% in two to three weeks.

   Every time somebody raises the issues of drying lumber and/or building a kiln, I try to remind them to consider the value of that material and what it would cost to purchase it.  With that as a basis, it becomes worthwhile in my opinion, to make the appropriate necessary investments so that the quality of the resultant product is first rate.  

   A good kiln is a good investment and if properly constructed and operated, it will provide you with an on-going source of good quality materials at very reasonable prices.  Like with the purcahse of good tools, a good kiln is a good investment. 

1. 
   crt2cu2 | Apr 25, 2003 03:33pm | #6

   Niemiec1,

   You certainly are more astute than I regarding wood drying via kilns and such. And I very much appreciate your postings. Lately though I have read a bit somewhere about drying wood in freezers. Could you enlighten me with any knowledge you have about this approach to stabilizing wood? Thanks

   sawick

1. 
   StanleyNiemiec | Apr 25, 2003 05:07pm | #7

   As a Wood Technologist (MS Penn St. '79), I am familiar with most processes for drying wood.   Drying wood is based on the principle of controling the chamber relative humidity and air circulation.

   Temperature is a component of relative humidity based on the fact that warmer air can hold greater amounts of moisture than cold air and warmer temperatures facilitate a higher rate of water evaporation.

   I do not see any particular advantage to freeze drying wood  --  yes water does still evaporate directly from ice (the triple point of water) but to dry wood properly you still need to control the chamber RH and you still need to circulate air. 

   The drying of wood requires a large amount of energy input  --  specifically to break the chemical bond between the water and the wood.  To freeze dry wood, you would use a large amount of energy to reduce and maintain the wood at below ambient temperatures and in doing so would drastically reduce the rate of evaporation.  As such, it does not seem to me to be a viable technology.  There may however be recent research in this area that I am not aware of. 

2. 
   JohnWW | Apr 25, 2003 05:24pm | #8

   If you only need to lower the moisture content a few percent, and you have two or three weeks to do it, the easiest thing to do would be to bring the stock indoors to a heated area.  Ideally, you could have the wood stacked and stickered in the same environment that it will be in when you start working on it.  If you dry out the wood to a moisture content below that of the shop area, it will only start reabsorbing moisture and shift dimensions while you work on it, causing endless problems with fitting.

   Boards 1" to 1 1/2" thick will stabilize fairly quickly once they come indoors, to prevent end checking have someone paint the ends of the boards with a sealant (old paint will do) or just stick duct tape on the board ends. 

   Sticker the stack with tall stickers (1 1/2 inches tall) and get the bottom of the stack well off the floor at least 6 inches, especially if the floor is at all damp.  Cement blocks with 2x4's laid across them make a good foundation for the stack.  All the base 2x4's need to be on an even plane to avoid bowing the stock.

   A small fan to keep the air moving around the stack will speed the drying out process.  Placing a dehumidifier in the room will also help but may not be necessary and could over dry the stock or dry it too quickly leading to "case hardening" where the outer dry wood shrinks around the still moist inner core causing damage to the wood.  You can only dry the wood as fast as you can get the moisture in the center of the plank to migrate to the boards surface. 

   Use very dry sticker stock to prevent mold from staining the boards where they touch the stickers.  The stickers and the base 2x4's can be fairly wide apart, every 3 feet or so and should line up vertically to prevent bowing the boards as they dry.  Placing additional weight on the top of the stack will sometimes help to control warpage.

   If the stack is wide, restacking it after the first couple of weeks, to move the inner boards to the outside, will help to speed the process and further even out the wood's moisture levels. 

   Have fun, John

    

   Edited 4/25/2003 3:14:58 PM ET by JohnW

4. 
   Dale | Apr 26, 2003 08:13am | #9

   A trick I learned years ago from Sid Boone, FPL if wood MC is below 20% MC put the lumber in your attic as you would in a drying stack.  I've knock down white oak from 20 to below 7 MC in less than two week during July in Okla.  Of course don't overload your attic.  It ain't easy work but poor folks have poor ways, : ' >.......Dale

1. 
   rwobee | Apr 26, 2003 05:29pm | #10

   Thanks to all who suggested solutions, but I dont have an attic, the jobsite is 40 kilometers from the shop, so storing lumber inside wont work, and the setup there is of a temporary nature (the shop was set up for just this project, and will be dis-assembled after we're done), so investing in an expensive kiln is also not going to fly. I'm thinking a plastic sheet - covered tent with a small fan driven electric heater on one end and a de-humidifier on the other,something that would lower the MC 4-6%. most of the boards are 6/4 and 8/4, and fairly wide. Has anyone ever rigged up something like this? would the heater exacerbate the incoming air,since warmer air holds more relative humidity? Anyone?

1. 
   fdampier5 | Apr 26, 2003 11:52pm | #11

   sounds like it should work except!  I'd lose the heater..

      Do NOT!  repeat do NOT!  dry to quickly..  that will lead to case hardening and case hardened wood is junk!

     One point.  make the plastic go all the way around. effectively sealing the wood inside.. There is too much moisture to be pulled out of the ground for you to ever get ahead of it..

     figure out a way to dump the water out of the dehumidifier outside, and no don't evan think of doing it by hand.. Way too much water involved.  hook a hose up or something..

    when I do mine I have to do it by hand but in two hours the bucket in the dehumidifier can be overflowing..  at times I hate my bucket brigade!

   Edited 4/26/2003 9:27:35 PM ET by frenchy