For me, one of the pleasures of woodworking is being able to dry your own wood. Not only does it save you money, but I also enjoy being involved in the process. The whole purpose of drying wood is to get the moisture content of the wood down to a point where the wood is more stable, and often somewhere between 8 and 14 percent.
There are a few different ways of drying wood. Stacking your wood up and letting the air flow around the wood is, of course, the oldest, and still very popular today, but if you want to accelerate the drying process you could use solar, dehumidification and high heat drying such as with a kiln. All of these are methods that work when drying wood.
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Outdoor air drying is a very common, and of course the cheapest way of drying wood, but for most of us, air wood is still too wet for furniture making and the longer it dries out o doors, it does not get any drier. If you are building fences, sheds, houses and other similar forms of construction, outdoor air-dried wood is just fine.
Most woodworkers who are making furniture are looking for a moisture content of between 8 and 10 percent. The reason for this is because when the wood is assembled and finished and put into a house, the moisture content of the wood generally stays around this level so there is minimal wood movement. This varies depending on where you live and what the average humidity is in your area. Where I live, and many others, drying wood outside is common, but the wood will seldom dry below about 12 percent at the very least, and more likely it only dries to 14% and can creep higher as wetter, winter weather descends. The only way to get wood that has been air drying outside, drier than 12% - 14%, is to either bring it indoors until it dries to around 8% or 9% which can take many months depending on the species and thickness of the wood.
The next best solution is to have, or make, some sort of a dryer, or kiln to help speed up the dying process. For most of us, there are only a couple of options, either a dehumidification or solar dryer. The other option for some, is to take their wood to someone who owns an actual wood kiln, which is like a big stove, where the wood is headed up for a certain length of time and this is what drives the moisture out of the wood.
Solar wood dryers are probably the most ideal dryer because they heat up during the day and cool off at night which helps to moderate the wood as it is drying, and except for the cost of building the solar drier, they are free to operate. The problem with solar is they only work well where there is sufficient sunlight during the day, if not they can be harder to regulate. A simple solar dryer or solar kiln is basically something like a one-sided greenhouse, south facing, that you can stack and sticker your wood in, and allow the air to circulate through the wood. As the wood heats up moisture is released, then at night as the wood cools, the moisture in the wood tends to even out, then the next day again as the wood heats and the moisture closer to the surface is released, then during the night the wood again regulates it'self and the cycle continues.
Dehumidification dryers have their own advantages and disadvantages. They, first of all, require a dehumidifier machine which costs money (new they are currently between $150 to $250 for a model suitable for a dehumidification dryer) and they require electricity to run.
Making your own dehumidification kiln or dryer is easy. It's basically a large wooden box, preferably somewhat insulated and it should be well sealed and with an easy access door, and you will need it to be someplace where you can run electricity to it. The box it'self can be made from inexpensive sheet products, like plywood, or OSB (oriented strand board) and can be made any size, but it's best to try and keep it large enough to accept the wood you want to put in, and somewhat the same size as the sheet goods you are using will help reduce cutting the wood needlessly. The frames are often 2x4 common lumber, half an inch and sheeted with sheet product such as OSB. You will need easy access to put wood into the dyer and take it out, and you will also want to, from time to time, open the dyer to check on the process and the moisture content of the wood.
It would seem that making a small, compact box would be more efficient, but in reality, a somewhat larger one is actually better. You need a box big enough to get your wood into and remember it needs to be well stickered once it's in your kiln, but also you need room for the air to move around the wood and around the inside of your drier. It is advisable to have some sort of a small fan inside your drier that helps to move the air around. You will get quicker, more consistent results when you can move the air around inside your drier.
Wood for your Kiln
You can dry any hardwood or softwood in your dehumidifier kiln, but hardwoods need to dry slower to help reduce cracking and checking and require closer monitoring. ALL WOOD that goes into your drier needs to be end-sealed, and it should be end-sealed with a recommended product. Latex paint, even several coats of it, does not always end seal properly and you can end up with cracks in the ends of your boards often requiring the ends to be cut off and wasting a lot of good wood.
Wood can be rough cut or plane, and my experience is that there is very little difference in drying time-based on surface condition. Thicker boards take quite a bit longer to dry, and should be dried slower. Unless there is a reason to go to a 4-inch thick board, 2-inch thickness is better in terms of speed of drying.
It's best to use the driest wood you can for "stickers", those are the thin strips of wood that we place between the boards. Wet stickers can telegraph lines into your boards as they dry which when it happens, leaves a permanent, mild discolored line across the board. A thickness of the stickers should be at least 3/4 inch, and one inch is better.
If you have the time, it is ideal, to allow any wet or green wood to air dry outside, for as long as possible, but even a few weeks can make a big difference. Cover your wood on top but leave the sides open as best you can. Basically, you want to keep rain and snow off the wood, but leave the sides open to the air. Do NOT wrap your wood in a tarp, this will trap moisture in and often builds a surface mold that is neither healthy nor advantageous. Air drying to start with will help reduce your costs of running the dehumidifier and will help to dry your wood slowly and to help to reduce checking and cracking in the wood.
You can put wet or green wood direct from a mill into your dryer. If you do this, you will want to make sure the dehumidifier is turned on very low and you probably will only want to run the dehumidifier either every other day or even every third or fourth day. There is a LOT of moisture in wood and green wood will very quickly fill up the reservoir in your dehumidifier, so you may want to add a hose to the tank to drain the water off externally ... but let his water drain into another pail so you can monitor how much moisture is coming off your wood.
What to do with Dried Wood
Over time your wood will dry down to a moisture content you want. When this happens it's time to take it out of the kiln and store it somewhere. If you want to keep it dry, storing it in an unheated shed or barn is going to allow the wood to absorb moisture from the outside air and there is every chance that it will revert back to the same moisture content as wood that is dried outside under cover. Wood is constantly releasing and absorbing moisture depending on what the content of the wood is and the content of the air around it so even if your wood has been dried to 8% unless you store it that way, it will can easily move back up to around 12% to 14% over months buy re-absorbing moisture in the air.
No matter what method you choose, the only real accessory you will really need is a wood, moisture meter. I have found them all to be reasonably accurate no matter what price they sell for. If you are looking for a good quality meter, one that you can use for drying your own wood and that you can take and use at any wood store for checking the moisture content of the wood, the ideal meter is a pinless one like the Wagner Orion 920, Yes it's costs more, but if you want accuracy and your wood dealer does not want you poking holes in their wood to check the moisture content of their wood, a pinless is the only way to go.
Yes, there are less expensive meters, and having any kind of a meter is better than nothing, but if you want a finer accuracy and a quality meter with a 7 year warranty, there are definely one to look at.
There is a lot to cover in kiln drying of wood and making various dryers and kilns, far more than can be covered here, but consider this a primer in making your own drier ... and saving a few dollars by drying your own mill selected wood ...
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Copyright Colin Knecht