Today we go inside the solar kiln. A cool 52 outside when I took the pictures, but 74 inside.
Let's start out with a rough isometric sketch of our kiln. Here it is below:
When you build your kiln, you are building in the same manner as building a small house. You use conventional 2x4 stick framing to build the walls. Insulate well in the cavities. I used regular batten insulation, but you should use 3" thick insulated sheets to avoid any moisture problems that might seep into the wall cavity. I used CDX plywood for the inside of the wall, and the outside of the wall too. I used 2x8s for the flooring joists. You want to insulate the floor too. My kiln is only 4' wide x 10.5' long. It holds about 300bd ft of lumber. Three hundred feet of oak weighs in at around 1500lbs. I've been in ones that you could easily walk into. A bigger kiln may need 2x10's for the floor.
The inside of the wall should be made so it will not allow water to pass through into the insulation. It can get pretty damp inside the solar kiln when a "green" load is put in. This humidity is important in the drying process as it keeps the outside of the lumber from drying faster than the inside of the wood. I coated the inside of my kiln with the same material that is used on mobile home roofs. You can buy it by the gallon at Walmart. I first sealed all of my inside seems with caulking though. Slop a coat, or two of this tar on the entire inside plywood part of the kiln. Get the seams really good. Make sure you don't wear your Sunday going to meeting clothes when you do this though, as it is a little messy.
Let it harden up for a day, or so, then paint over it with black paint. The black surfaces absorb the heat. I later had the thought of using adhesive roofing membrane on the inside of the kiln instead of the tar stuff. It might got too soft in the heat though? It would kill two birds with one stone. It is waterproof, and it's already black. I don't think it would work on the floor though as the floor takes a lot of abuse. The weight of the lumber pile would soon make your first layer of stacking sticks part of the membrane!
When you are done with that mess, you want to make the fan wall. I had some black sheet metal I made mine with, but the CDX would work too. I would not recommend the sheet metal on the inside for the walls though because it is impossible to get a perfect seal, even if you caulk the seams. I tried this with my electric kiln with no luck at all. I put my fan wall together inside the kiln with screws. You might want to do the same, or at least use a nail gun. Tempered glass gets really angry when it gets vibrated a lot form pounding. a note on the glass, I used old patio doors, but old windows work too. Just ask any home improvement guy if he would save some for you next time he does replacement doors, and windows. This is what I did, and in no time at all, I was buried in old windows, and doors! Keep the fan wall about 12" from the back wall. This gives the fan some breathing room. Below, is my fan wall.
I use a pontoon fan. Look how rusty that thing is. It has never had a drop of rain water on it either. That is from the moisture from the wood. See the importance of the tar moisture barrier? I also later added the little attic fan that blows across the glass panels, but it isn't really needed. I had it laying around here, so tossed it in. A bigger kiln needs more fans. Air flow is very important in drying lumber.
I laid on my back to get you this picture, below. This is a shot of the fan wall to the back wall of the kiln. The fan sucks in fresh air from the upper vents, blows across the glass to the kiln's front, and through the lumber pile, then out the back (bottom) vents with the moist air.
Here is the inside of the kiln, below.
Next time we will talk about how to actually dry lumber with this thing. Believe me it works, and it works well! You serious woodworkers will save a small fortune in lumber. Cabinet cherry is .55 cents a board foot off of the mill right now. Make your wife happy, and make here some cherry kitchen cabinets, or better yet, make my wife happy, and make some for her.
Thanks for reading everyone
Kevin Koski Dry Kiln Owner and OperatorCurlyMapleWood.com
www.curlymaplewood.com
