Replies

1. 
   Rennie | Sep 15, 2006 06:41pm | #1

   The current issue of American Woodworker has a very good article on building a solar kiln.

   Rennie

   A man is a fool if he drinks before he reaches the age of 50, and a fool if he doesn't afterward.
   Frank Lloyd Wright

1. 
   Qara | Sep 17, 2006 04:16pm | #15

   Renny,
   a solar kiln is of no use, unfortunately, at a latitude of 48 degree.
   Qara

2. 
   frenchy | Sep 16, 2006 01:28am | #2

   qara,

    What are you asking?  It sounds like you'd like to do it and want permision?

     I hope that doesn't come off as smart azz. If so I apologize..

     Small Kilns work and there are countless versions of them.. part of the kiln drying process is learning though..

      You need to dry slow enough to not case harden it or cause other problems..  yet everybody wants their wood right away..

       I found that I can achieve the same effect simply by putting wood indoors during the heating season.. I can fully dry wood down to 7/8/9%  in as little as 45 days depending on the species of wood, the way it was sawn and  a whole handful of factors..

        I like the drying process, there is a challege getting wood quickly ready without degrading it.  start with cheap wood and practice on stuff you won't mind losing.. then go to the prized woods..

    

    

1. 
   Qara | Sep 16, 2006 05:19pm | #3

   No, I need no permission to build a kiln. I build one.
   I pretty much know the theory.I know of various problems of case hardening.
   What I have not seen is actual examples of small kilns and a discussion of manual viz. automatic operation (apart from an obvious price difference). There is a great many things to measure in order to optimize the drying process, but you need not measure them all.To keep the lumber in the shop during the heating period restricts the working time to that period in my case, since later the outside temperatures become relatively high and the humidity is close to 100%. My shop is in the basement. I use a dehumidifier, basically to protect the tools, but this means the lumber stays only reasonably dry if it was that way to start with, but would not dry down from 15-18% to say 7-9%.
   The only way out is to store and dry the lumber in a place at an equivalent low air humidity, which your shop seams to be during the heating season.
   Here comes the kiln. Other solutions, as yours (I also have used so far), are quite unsatisfactory.
   Quara

1. 
   frenchy | Sep 16, 2006 05:47pm | #4

   Qara,

    I'm glad you didn't take offence to my last post, just now rereading it it could have been easily taken wrong..

          I live in Minnesota and during the heating season the moisture from wood drying is a great benefit.. I don't know where you are.  I also have enough room that I can dry in the house without a wife tripping over it..

          My take on Kilns is that if they are indoors they take up more space than just the wood does and if they are outside they are never large enough..  A friend has a whole barn as a Kiln.  big 30 x50 foot place and right now it's so packed full of wood he's recieved over the years that he's now resorted to storing it outside under tarps..

      He slow dries the wood over the winter and by summer it was ready.

     The method he uses is a scrap woodburner in the basement and the smoke slowly works it's way out pipes under the floor. 

     Actually it's not really packed.  In the the part of the barn away from the entry  is neatly stacked and the aisles are virtually empty.  However near the entryway it's jammed to the rafters full of wood on stickers and in the aisles there are mounds and mounds of wood just laying there.. wood that he was going to get to some day but apparently the around-to-it's haven't shown up yet.

       My guess is that he has around 100,000 bd.ft. stored there..

       Anyway I'd guess it really depends on how much wood you want to dry and how much you want to store..

    

    

    

    

1. 
   Qara | Sep 17, 2006 12:54pm | #10

   frenchy,
   my fist remark is that I started this discussion with sufficiently general, I intended not to narrow down the discussion in the beginning. So, many interpretations were possible, don't worry about the first sentence in your contribution!
   I agree in many points with you.I live in the Black Forest it rains a lot, the heating period is long, but really cold weather is only in January.
   I have not so much space in the shop or in the house to keep enough dried wood for the year.
   Air drying is good, if it is done carefully. Drying in a mild climate, as the technologists say. Apart from the fact that I never reach low wood moisture, the condions in the stack are often very inhomogeneous. A friend of mine kept some walnut in a shack in the mountains for years, nothing was below 13% but there were pieces as high as 19%.
   One has to reshuffle the stack occasionally.You mention discoloration of kiln dried wood. This comes, to my knowledge, from the initial humidification in the drying process to remove inhomogeneity and/or remove mild case hardening. Stains are left in wood like oak, maple or walnut and the surface becomes dull.I don't know if it can be avoided completely.
   There is more in the forum later.
   Qara

1. 
   mufti | Sep 17, 2006 01:44pm | #12

             Just for interest, I have had Ercol furniture which, not being needed or of value, I have recycled. I read somewhere that in order to eliminate movement the firm carefully kilned their timber to a low m/c, held it there and then took it up to a high m/c, then brought it down again before use. I do not know how many times this was done, but the end result is tables with breadboard ends which do not move and no warping.

   I guess they effectively eliminate the elasticity of the wood cells whist preserving the essential strength of the wood, usually ash, elm or the like. We can not do this but I profit by the recycling.

2. 
   Qara | Sep 17, 2006 04:10pm | #14

   mufty,
   I know that at the end of the drying schedule the wood is brought up to higher moisture content, to the one it is used finally. This is to archive a uniform moisture content over the thickness of the wood.
   Wether this process is done repeatedly, i.e.increasing and decreasing the moisture content, is unknown to me, but interesting.Concerning elasticity I heard that bow makers dry their bows to low values before the bows are used. Elasticity only comes with dried wood.
   Qara

2. 
   frenchy | Sep 16, 2006 05:54pm | #5

   Qara,

        You mention a point I don't think most people really understand.. If you slow dry wood without additional heat or dehumidifing all you really need to do is check for dryness.. the faster you dry wood the more careful you need to be and the more you need to check stuff.

    Air drying in the right climate is really the best method in my humble opinion.. if you look at air dried black walnut you will see much more vivid colors and grain.  Kiln dried walnut may as well be brown stained wood in my humble opinion..

      I have only rarely seen case hardening, honeycombing, or some of the other ills of Kiln drying with air dried wood. Yet it's a constant threat with Kiln's

    

3. 
   JohnWW | Sep 16, 2006 06:11pm | #6

   Quara,

   I'm not sure that I follow you on bringing wood into the shop to dry and being restricted to the winter. 

   The wood never has to be reduced below the point that it is at equilibrium with the air in your shop, so if the equilibrium point for the moisture content is at 12% in your shop in the summer, there is nothing gained by trying to get it any lower, in fact it will only create problems if the wood starts to absorb moisture as you work with it.

   John White, Shop Manager, Fine Woodworking Magazine

1. 
   frenchy | Sep 17, 2006 12:45am | #7

   JohnWW

    You're right to a degree. I've been carefully told that the "water" in wood needs to be removed completely for the wood to be stable.  He called it Bonded water. another words the water in the wood cell.

         Once that has been removed the moisture that wood absorbs has a nominal effect on it compared to the original water seeking to escape..

     Now commmon sense tells me that some original bond water must remain or we'd get to 0% moisture.   

    I agree that it sure seems foolish to draw moisture down below what the wood will normally be in, yet wood that I've gotten to 4 or 5% moisture (winters sure get dry up here in Minnesota)   and then allowed to raise to the moisture in the house normally is sure a great deal more stable than wood I start to use as soon as it approaches  12 or 14%.

          

1. 
   DonaldCBrown | Sep 17, 2006 01:36am | #8

   "Now commmon sense tells me that some original bond water must remain or we'd get to 0% moisture. "I guess there are many versions of common sense, but your discussion confuses me.Water in the cell cavity is called free water in the wood technology literature. Once the cell cavity has been emptied, water remains in the cell walls. This water is called bound water, which may be what you are calling Bonded water. But please note that bound water is NOT in the cell cavity. With no water in the cell cavity, but with the cell walls saturated, wood is at what the wood guys call the fiber saturation point. The wood will begin to shrink only when some water leaves the cell walls.Wood can, indeed, be dried to zero percent moisture content. The minimum dimensions of a block of wood are achieved at zero moisture (oven dry) and are the reference for determining shrinkage at points between zero moisture and fiber saturation point.There's nothing original here. I am simply repeating the basic criteria for discussing wood drying contained in Bruce Hoadly's "Understanding Wood."

2. 
   SgianDubh | Sep 17, 2006 01:44pm | #11

   Donald, I see it slightly differently. Free water is the water that is to be found in the sap conducting vessels (tracheids) of the wood. In hardwoods (angiosperms) these are the mostly live xylem cellular 'pipelines' from root to leaves- the sapwood. In gymnosperms these are primarily the long thin walled sap conducting tracheid cells where liquid is transferred from one cell to the next very rapidly via osmosis-- the cell walls at each end of these cells are extremely thin, barely existent I'd say.

   Once free water has left wood, all that's left is bound water which means the wood will be between about 23% MC and 33% MC at FSP (fibre saturation point.) The FSP of wood depends on the species and the extractives content typically found in that species.

   I consider all liquid still within the (whole) cellular structure as bound water. In other words it's water that cannot simply drain out-- it must physically pass out of the cell to somewhere else, and this means both the fluid within the cell and whatever fluid is in the cell walls too. Slainte.Richard Jones Furniture

3. 
   DonaldCBrown | Sep 18, 2006 01:50am | #17

   Richard-I bow to your superior knowledge and experience. I was quoting Hoadley in an attempt to clear up the confusion of terms and definitions that had preceeded my post. But I'm puzzled by your image of free water simply draining out of a piece of wood. Is that actually how wood reaches fiber saturation--gravity forcing the water down and out? I, for some reason, imagined a more complicated process involving osmosis, vapor pressure, and other mysterious forces.Another question while I have your ear: If free water is the water found in sap-conducting vessels, then what accounts for the free water in heartwood? I believe the moisture content of freshly cut heartwood (either soft- or hardwoods) is well above fiber saturation. Is that the ex-sap-related moisture that once was involved with nourishing the tree but is now just sitting there?Regards,
   Donald

4. 
   SgianDubh | Sep 18, 2006 03:40am | #18

   One of the few woods where water will simply drain out of the dead heartwood as if the wood was rather like a bundle of drinking straws is red oak, Donald. Red oaks form very few tyloses- the bubble like forms that are created in the dead, inactive, former sap conducting tracheidal tissue of heartwood. Heartwood is dead xylem, ex sapwood. Dead xylem no longer has active cells. The living cellular matter has left the wood, but the cells themselves remain.

   In living angiosperm trees (hardwoods) the living sapwood is akin to the bundle of straws I mentioned. Water and nutrients is conducted upwards via root pressure and evaporative pressure at the leaves. The water at the base of the tree is drawn into the roots and at the top a space is created by water evaporating out of the leaves. Osmosis comes into play when discussing the sap conducting system of gymnosperms-softwoods. Softwoods don't form pipe networks as do hardwoods and water/nutrients are transported via osmosis from cell to cell up the tree, and similarly down the tree via the bast or phloem.

   If you watch a freshly felled tree you can sometimes literally see water exuding out of the living sapwood.

   The answer to your second question is that the old sap conducting tracheidal tissue (heartwood) of both hardwoods and softwoods are still capable of holding water. They no longer actively conduct it, but the spaces are still there, albeit in most hardwoods they are much blocked off by the tyloses that form once the sapwood is converted to heartwood-- red oaks being one of the major exceptions as discussed earlier. Slainte. Richard Jones Furniture

5. 
   frenchy | Sep 17, 2006 04:52pm | #16

   Thanks Donald,

        I own a copy of Hoadly's book and have used it a lot in the past.. Kiln operators all seem to have their own take on the subject matter and offer confusing information.. It's nice to go back to the source..  

6. 
   SgianDubh | Sep 17, 2006 01:44am | #9

   The term you're grasping for frenchy is 'bound' water-- the liquid bound up in the cellular structure of the wood.

   The effect you're describing (regarding movement of wood) is the view expressed by many timber technologists or scientists is that once the wood cells have dried to as low a point as 3% or 5% MC that the cell walls have become permanently distorted by this extreme drying. Even if the wood gains enough moisture to reach fibre saturation point (FSP) the cells will not revert back to their former shape because of the permanent cell wall deformation. Extremely dry wood takes on a permanent sort of set in other words.

   Not all timber technologists agree with this viewpoint, but it's well worth noting. Slainte.Richard Jones Furniture

2. 
   Qara | Sep 17, 2006 02:45pm | #13

   John,
   the wood will eventually leave the shop as furniture, will then be in an environment of equivalent humidity of 7-10 % (in the heating period) and shrink. It is therefore structurally unstable.Wood which had been brought down once to low humidity is structurally much more stable, and it will move less at various humidities down to the one which it had been dried once. This is at least my experience.Quara