- Drying time is unknown. It can take months or even years.
- During drying, the wood dries at an uncontrollable rate. It becomes prone to checking and cracking, devaluing the wood.
- Finally, wood pieces that are air-dried or dried in a standard kiln will warp.
To solve all of these issues, milled wood of all shapes and sizes are placed in a vacuum kiln.
The kiln is a simple-looking, reinforced metal container about 6 feet wide x 6 feet tall x 20 feet long. Once the wood is placed inside, a vacuum pump begins to remove all the air from the chamber. With the wood being subjected to vacuum, water vaporizes off extremely quickly maintaining the integrity of the wood.
However, there is another challenge in applying a vacuum: temperature drops dramatically. And when temperature drops, it becomes harder and harder to pull the water out of the wood.
So, the solution is simple, right? Simply heat up the kiln. Well, not so fast! Simply heating up the kiln won’t work because heat wont transfer across a vacuum. The kiln under vacuum becomes like a giant, reverse-thermos: it keeps the cold in and the hot out.
But there is a way around this: heat the wood up inside using electromagnetic radiation – which does travel across a vacuum. As scary as the term might sound to some, electromagnet radiation includes frequencies like radio waves, microwaves, infrared radiation, all things we encounter daily.
The vacuum kiln of The Heartwood Mill uses radio waves to heat up the water molecules in the wood. Now with the wood under vacuum and being heated up by radio wave, the process of creating crack-free, un-warped wood takes a matter of days instead of months or years.