Here are some pics I thought I'd post for anyone interested in seeing lumber go through what it does to get it ready to be made into something you'd find in your home. Some of you may remember this lumber in pics I posted when loading it onto a trailer. The walnut and maple trees were cut, then the logs were sawn into boards, and then we loaded it onto the trailer where it sat for a few days waiting to get into the kiln. Here are some pics of it coming out of the kiln completely dried.
This wood is walnut and maple, and is dried to 6% moisture content. This type of kiln used is a dehumidifier. There are different ways to dry wood/lumber. In each of the different ways the wood is stacked the same... stacked with small narrow strips ("stickered") between each layer so the air can circulate over, under, and around each edge. Air flow is critical so the wood dries evenly and also so mold growth is not happening while you wait.
1). Air drying
This method is free, but "you get what you pay for". The lumber is stacked and usually left outside or in a large barn/storage building. This is definitely the slowest method possible. It will take a min of a year to get it even close, but will still need to dry... usually a couple-three years can be the wait expected if choosing this method. It is still not in the best of shape after waiting years on it, although it can be cut, worked, and used for projects, the wood still retains more moisture than if dried in a kiln. Air drying is not the best way to dry lumber because 1), it takes a few years on it to be ready to rotate into the "workable" stock, and 2), it also has a higher moisture content than kiln dried lumber. This is because wood cells (shaped similar to the shape of a football) will get a hole poked into them when kiln drying which causes the cells to break which then makes them release moisture. The cell is no longer able to retain water/moisture like a vase would no longer hold water if a hole were drilled into the bottom of it. Air drying does dry the wood and get the overall moisture content down to a "workable level", but some of the cells do not get punctured and will retain more moisture... not a good thing after it's turned into a piece of furniture (or whatever).
2). Solar kiln
The best choice if available. It dries the wood slowly (longer than a normal kiln) which is better for the wood. Slow changes are always best, like when we've talked about ivory for knife handles... humidity changing slowly is OK, rapid changes like with overnight shipping are not good for the material and usually result in cracking.
3). Dehumidifier
A good way to dry wood with few cracks, and still have it fairly quickly. This load was in this type kiln for 18-19 days, not so long to wait.
4). What is commonly called a "pressure cooker". This type kiln dries very quickly, about a week, and because of the speed it most generally produces lots of cracks, checks, and less than the desired grade when finished. Usually found in high production type facilities, they generally cut around the bad spots and use what they can. They are willing to get a smaller yield just because of the shorter wait time.
Our two youngest sons, Daniel and Andrew, are standing in front of one of the kilns to give you an idea of the overall size. Track on the inside floor and wheels on the carts allow for easy loading and unloading once a load has been dried. More rails (or track) are then placed in front of the kiln so the rack or cart can be pulled out for inspection, and loading onto a trailer or truck. A shot of the digital therm, and a a close up shot of checking the moisture content. This lumber was dried down to 6% content. It will need to sit in the shop for a few days before "working it" so it can have a chance to acclimate to the moisture inside the shop. It's always a good idea to let the wood adjust to where it's going to be when working it like if you were laying a hardwood floor... you'd want to bring the wood into the house where it's going down, and let it sit there and adjust to the temp/humidity in that room for a week or before working with it opposed to just taking it off the truck and nailing it fast.
You can see some of the boards have quite a curved to them (like the bottom of a rocking chair). This is due to imperfections in the wood. Knots will cause the wood to shrink up around them and usually result in a wide crack right through the knot itself. This shrinkage will cause the wood around that area to pull in thus resulting in the extreme curve in a few of the pieces. This lumber will then be planed smooth, and to a constant desired thickness, once it has had time to adjust nicely to it's new environment.
I hope you found this interesting and I didn't put anyone to sleep.
Best,
~dale
P.S. I believe some of this may find it's way into the canoe project.
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