Kiln Drying 101

Kiln101

A kiln is an amazing tool to have if you’re interested in cutting and drying your own wood. Not only does it give you control over the condition your wood is in, but if you’re feeling especially crafty you can even build the kiln yourself.

As with any tool, the kiln is only as effective as you allow it to be; if you don’t understand how it works or how to use it properly then you’re not going to get the results that you want. To that end, here are some basics to keep in mind when learning how to use a kiln to dry your own wood.

How Do Kilns work?

The basics of a kiln are pretty simple: A heat source makes the air inside of the kiln warm and dry, pulling moisture from the wood that you place inside. As more water is removed from the wood, the wood will shrink and become harder and less flexible. This is why wood is dried before being used for construction or woodworking projects, as you don’t want wood that will bend or shrink after you’ve used it.

It can take up to two weeks or longer to dry wood in a kiln, depending on both the temperature and the moisture content of the wood. Both the internal and external moisture content is checked after drying, and if the two are out of balance then more drying time is needed.

Temperature Considerations

A lot of wood kilns use relatively low temperatures compared to other heating equipment, with many woodworkers drying their wood at around 100 degrees Fahrenheit (though this may range as low as 90 degrees or as high at 110 degrees.) This is done for two reasons. The first is that too high of a temperature can damage or warp wood by drying it too quickly; the outside will dry and shrink while the inside of the wood is still moist and flexible. The other reason is that the temperature has to be maintained over time and it is much easier to hold a kiln at around 100 degrees for weeks than it is to hold it at a much higher temperature.

Kiln Insulation

The better a kiln’s insulation is, the easier it is for the kiln to hold heat over time. The type of insulation used depends a lot on the size of the kiln and the materials it’s made of; some kilns used by lumber companies are large enough you can drive large trucks into them, so their insulation needs are quite different than what would be used on a small home kiln.

Regardless of the size or the insulation used, it’s important to insulate from all six sides. Insulation at the bottom of the kiln and on the door is just as important as other parts of the kiln as any wall lacking proper insulation will make it harder to maintain a consistent temperature.

Air Flow

Having good airflow within a kiln is vital to even drying. Depending on the size of the kiln and where the heat sources are located, some of this airflow is accomplished by the natural rise of hot air and it sinking back down as it cools slightly. The kiln needs to be large enough that wood can be stacked or otherwise organized to allow for airflow between pieces of wood, however; without this flow, it will take significantly longer for the wood to dry and it may not dry evenly.

Insect Concerns

The temperature and the type of heat source used in a kiln can sometimes kill insects that have burrowed into wood or laid eggs on it, but that isn’t always the case. Homemade kilns that rely on light bulbs for heat, especially, often lack the heat intensity required to kill insects.

Even larger kilns aren’t guaranteed to kill all of the bugs, particularly if there’s a larger amount of wood being dried. If insects are a concern, it’s important to be aware that with some kilns, you may need an additional solution to get rid of them.

Have you ever worked with a kiln before? What was your experience like?

WoodworkingTalk.com

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