Thermally Modified Wood Started with the Vikings!
Thermally modified wood products are still considered new to us here in the United States. But they’ve been widely used for over 20 years in Germany, Austria, Norway, Switzerland, Japan and Italy for both interior and exterior use. However, it was the Vikings, centuries ago, who apparently first discovered that burning the surface of wood made it more durable and better suited for exterior use.
Vikings Discovered Thermally Modified Wood!
Centuries ago, the Vikings learned to overcome natural wood’s shortcomings by treating it with fire. They discovered that burning the surface of cut wood made it more resistant to the effects of outdoor exposure. Consider this the first instance of wood’s thermal modification for construction purposes!
It was only within the last century that Europeans perfected the thermal modification process. By adding steam to it, this further alters the structure of wood, making it more impervious to rot, mildew, and decay.
What Does Thermal Modification Do to Wood?
Thermal modification is now a highly technical computer-controlled process carried out in specially designed high-temperature kilns. Only heat and steam—no chemicals—are used, which makes the process green.
When hardwood is thermally modified, the process permanently alters the wood’s chemical and physical properties when temperatures over 400˚F are reached. This is very different than the way wood is dried traditionally in a kiln. Kiln drying only reduces the moisture content of the timber (to an acceptable range of 6-8%). The thermal modification process reduces the wood moisture content down to a very low range of 0-5%.
Two of the popular ways to thermally modify wood are in open systems (not under vacuum) and closed systems (under a vacuum). Open systems reduce the moisture content to zero, but cause more stress on the wood and its physical properties. Closed systems reduce moisture content to approximately 5%, resulting in less internal stress. Thermally modifying hardwoods has the effect of drastically reducing the equilibrium moisture content. Put simply, the physical structure of the wood is changed, resulting in changes in the physical properties of the hardwood.
What Physical Characteristics are Different with Thermally Modified Hardwood?
Thermally modified wood produces material with outstanding dimensional stability and rot-resistance because of how it changes the cellular structure of the wood. The cells in wood have their ability to transport water reduced, resulting in a water resistant effect. The sugar content in the wood cells is also reduced, minimizing the food source for mold and fungus. These two physical changes in the wood result in a hardwood product stable and durable enough for exterior applications – much as the Vikings used it.
The color of the wood is transformed, and this color extends throughout the thickness of each board. The color of “medium-treated” wood varies from light to golden brown, while the “intense-treated” wood is a chocolate brown. Because of their stability and color change, thermally modified products are considered an environmentally friendly alternative to engineered and exotic products.
Why is Thermally Modified Hardwood a Great Product?
Thermally modified hardwood is a natural, chemical-free material – a safe, green alternative to chemically preserved wood. The deep rich colored wood is excellent for exterior applications where weather related decay and stability are essential. You can expect years of service with minimal maintenance from this sustainable alternative to tropical imports such as teak and ipe.