Whether you are milling for yourself or for a customer, you should make proper stacking a priority. Wood continually exchanges moisture or water with its surroundings, although the rate of exchange is strongly affected by the degree to which wood is sealed. However, the United States Division of Agriculture Forest Service and others are conducting research in solar drying for Third World countries located in the tropics. Tom, there are many of us who mill our own lumber and air-dry it, without using a kiln.
If you get the water content down to some percentage as measured by a probe and it feels dry to the touch, you can seal it on all sides and then it shouldn’t matter how much water is in the wood since it will be sealed in. You also want to avoid over drying or drying too fast. Left in the woods through at least one season of dry winter air, the logs would lose their live wood moisture content in excess of ambient humidity (about 20%) through evaporation in warm weather and, more slowly, via sublimation after a frost. It is illegal to burn anything except untreated wood and manufactured firelogs.
In general it is better to have wood a little shorter than ideal rather than longer, first because it is no fun trying to jam too-long pieces into the stove in January and second because shorter pieces are easier to handle and quicker to dry. Wood products used outside but protected from direct precipitation will stabilize with the surrounding environment at about 12% MC in the humid southern states, but may stabilize to as low as 6% MC in the arid Southwest. But I suppose that firewood could get very dry by natural seasoning in desert conditions. Rate of drying largely depends on climatic conditions, and on the air movement (exposure to the wind).
Kiln operators and quality control personnel deploy hand-held wood moisture meter products to conduct as many spot-checks as needed to verify the mill’s kiln-drying efficiency. Also, the weaker cell structure of lower density wood reacts more favorably to the stress of drying rather than resisting and checking. Originally, pre-dryers were used in areas where the normal air drying season was fairly short, but their use has spread to other areas of the country.
It works by blowing warm air to the Trocknungsbox, where the wood chips are dried on pitched and flat grates that have a drying capacity approximately 10,000 cubic meters. If you have time and are willing to sacrifice some wood, you can take a piece cut off part and dry it out in the oven. For most woodworkers, running their own kiln to quickly dry lumber may be impractical or excessive. Bow – A form of warp, bow describes a deviation flatwise from a straight line drawn from end to end of a board. Drying the wood in the sun is faster, but it weakens the wood and makes it more likely to crack.
FSP for most wood species falls in the range of 25 to 30% MC. It becomes increasingly hard to remove water from wood after reaching the FSP. The drying time is affected by the amount of moisture in the air, the air temperature and the thickness of the coats. The EPA test method requires wood with a moisture content between 16 and 20 per cent (19 – 25% dry basis) and when the wood is outside this moisture band, the stove’s emission rate goes up. So even the best wood stove’s performance will suffer if the wood is not in the right moisture range.
Not surprisingly, this can result in drying problems, most commonly twist—where one of the corners of a board is raised up out of the plane of the other three corners. I decided that sawing off the part of the end grain that has the fast drying cracks was better because I would have to saw off that part anyway if it had the end grain sealer in it. However, it is a question as to how much has to be sawn off to remove the sealer impregnated end, or remove the unsealed cracked end grain. Ideally, wood is dried to that equilibrium moisture content as will later (in service) be attained by the wood.
B, below)—floor, roof, front, back and sides—that can be built in the comfort of your shop (Photo 1). Insulation in the walls and floor helps the kiln retain heat, which helps speed the drying process. To accomplish this in a shorter period of time, or in more humid environments, a dry kiln must be used to dry the wood. The Oregon Cooperative Extension Service publishes free plans for a great little solar dryer suitable to their cool and foggy weather.
Much like the pith itself, juvenile wood is very unstable, and has an elevated rate of longitudinal shrinkage; this increased shrinkage rate pulls against the mature wood and causes it to contract and deform either along the face of the board (bow), or along the side of the board (crook). Figure on cutting enough stickers per board course to lay them every 2′ along the length of the boards. With a few months of hot weather, even wet wood dries to a cracking dry state, perfect for winter burning.
The theory goes that its cylindrical form causes a chimney effect, in which air entering the holz hausen is drawn upward by the heated mass of wood in the center, speeding the drying effect. The relative humidity inside the kiln — or anywhere — is calculated using these two measurements. If you need further information regarding the drying of lumber or other wood products, contact your county agriculture Extension agent or a forestry or agricultural engineering specialist at the University of Kentucky.
This drying method is well suited to the needs of timber companies, which have to dry timbers of varied species and thickness, including refractory hardwoods that are more liable than other species to check and split. If the relative humidity is 0.50, then using the Hailwood-Horrobin equation the moisture content of the wood at equilibrium is about 7.4%. The time to reduce the lumber from 85% moisture content to 25% moisture content is then about 4.5 days. The process of artificial or ‘oven’ drying consists basically of introducing heat.
Although the analysis was done for red oak, the procedure may be applied to any species of wood by adjusting the constant parameters of the model. The great amount of energy that must be expended to drive the water out of wood. Build furniture from 8% wood and put it in a 14% enviroment and you have all sorts of problems. Because wood is a hygroscopic material (meaning that it readily takes up and retains moisture), it is impossible to prevent moisture from entering dry wood. The moisture content of wood used in interior applications typically ranges from 6 percent to 10 percent in Missouri.
B). Attach the front panel and the roof (Photo 7) and set the vents (Photo 8). Your green wood is on its way to being kiln-dried. The only practical way homeowners can do this is to allow the sun and wind to dry the wood for them. Incidentally, several small pieces of wood will dry more quickly than one large piece; there is no reason why the sample should not be cut up – as long as this is done before it is weighed. Wood is often sold wet and green — right off the stump — or aged for just a few months. This occurs naturally, and it occurs throughout a wood product’s lifespan even after it has been harvested and kiln-dried for human use.
Permissible drying degrade; because aggressive drying schedules can cause timber to crack and distort. It’s important not to rush the drying process too quickly, but once a wood pile has safely reached EMC, it may be necessary (especially during humid summer months) to bring the MC down even further for a specific project. If the wet” lumber weighs 4,700 pounds per thousand board feet (lb/mbf), and the dry lumber weighs 2,300 lb/mbf, then the water removed weighs 2,400 lb for every mbf of lumber. If the oven temperature is too high, some of the wood components can be driven off.