Because they capture the energy of the sun, solar kilns are becoming increasingly popular for the hobbyist or professional woodworker who wants to dry his own lumber, and with good reason; dried wood sold at a lumberyard is expensive. Wrapping planks or logs in materials which will allow some movement of moisture, generally works very well provided the wood is first treated against fungal infection by coating in petrol/gasoline or oil. Apply a non-hardening, silicone caulk to the outer surface of the frame to provide a seal between the plastic and the wood. For this reason, you might find that air drying first is a better procedure, followed by 2 weeks of kiln drying. The significant advantages of conventional kiln drying include higher throughput and better control of the final moisture content.
I have mentioned this stuff before and many of you are familiar with it. For the Anchorseal virgins in the audience, it is a wax emulsion used in the forest industry to seal wet or green wood. This will allow the wood to acclimate to the humidity level INSIDE your home rather than out in a barn. Forget the d/h unit; just use a heat and vent system like a conventional kiln does or a solar kiln does. The key is to build up a thick, obstructing film that will inhibit moisture from escaping at the ends of the board. Elevated temperature – Type of kiln that typically operates with temperatures in the range of 110 to 211°F.
Since I built this kiln I’ve found a company that I can get to roll the angle iron diameters needed for the top and bottom ‘rings’ of a Ring Kiln. The fourth kiln I built in 1985 has twenty five mullite two-inch U-shaped tubes in the chimney. Wood dries from the outside in”; that is, the surface of the wood must be drier than the interior if moisture is to be removed. Eventually, the wood will reach a moisture content that is in equilibrium with the surrounding ambient air and humidity.
Temperatures inside the kiln range from 120 degrees Fahrenheit to 190 degrees Fahrenheit, depending on the stage of drying. Kiln is made from soft bricks and is about 150liters chamber for vessels and it is build from 255 soft bricks. It may be more economical to harvest lower grade trees or even buy the lumber and then sell the veneer quality trees. Given the choice of not having a kiln because you cannot afford one, and building this cheapo but generally reliable kiln, it is an easy choice. The rate at which wood dries depends upon a number of factors, the most important of which are the temperature, the dimensions of the wood, and the relative humidity.
Based on the chosen technology, the control system of wood drying maintains the desired temperature and humidity of air independently. It was expressly designed for kilns with an interior of exterior grade fir plywood. However, if there’s not enough solar panel area, there’s the risk of never being able to dry the wood below 15% moisture content (MC). Cases of wood plugs used to cap off conduit in building projects sit next to the copy lathe that churns them out. Note that there is nothing natural about drying timber in that a tree grows, dies and rots as a normal cycle.
Regarding solar heated kilns: I believe that solar kilns will not work well when the average outside temperature is much under 50 F. Plan on 3 loads per year. Handbook No. 402, USDA Forest Service, 110 pp. (For sale by the Superintendent of Documents, Government Printing Office, Washington, D.C. 20402). The drying of wood is thus an area for research and development, which concern many researchers and timber companies around the world. Just like we do with the more substantial gas and electric kilns that we build here – only much cheaper.
Poor support while drying will cause the weight of the lumber in the upper layers to sag or otherwise distort the lumber near the bottom. Planing reduces face or surface checking and cracking, and uniform thickness helps to prevent warping during drying. I’ve since unloaded the burn only to find that we must have shut it down just a bit too early – only the bottom third of the kiln has carbonised properly and the rest are ‘browns’ as they’re called. You may obtain more detailed information on this subject from USDA Agriculture Handbooks Number 188, Dry Kiln Schedules for Commercial Woods. Kilns can be loaded directly with fork lift trucks or track & trolley systems can be supplied.
The kiln heats when solar energy enters the clear glazing and is absorbed on the black painted interior surfaces. I’ve got a fairly local engineering company who are interested in getting the sides cut and bent so there’s now a vague chance I’ll make a full 6/7′ diameter kiln next year – don’t tell the wife – on the drive at home. When deciding on kiln size, consider the maximum capacity of the kiln in board feet to be 10 times the roof area in square feet.
In total, this lumber, with the addition of a little 4/4 poplar, made up nearly 1,000 bd. ft. Now it’s not a good idea to dry wood of different species in the same batch, let alone wood of differing thickness. Bob’s system uses the wood waste generated by his sawmilling business to heat the kiln, he can dry 6000 BF of lumber in about 100 hours using only the waste from his woodmizer, the system was cheap to build and most of the lumber for it was cut on his sawmill, the basis for the system is a non pressurized boiler.