The Thermal Modification Process

What is Thermally Modified Wood?

VikingWood™ is a natural, chemical-free material which is treated under extremely high temperatures (400oF+). Sugars are cooked away leaving a safe, green alternative to chemically preserved wood.

Under this extreme heat, the hardwood is “thermally modified,” permanently altering the wood’s chemical and physical properties. The thermal modification process reduces the equilibrium wood moisture content down to a very low range of 5 to 6%.

The VikingWoodTM Thermal Modification Process

AHC Hardwood Group installed the first North American pressurized closed thermal modification system at our facility in Cleveland, Georgia in 2016. The closed-system pressure vessel provides thermally modified lumber for use in applications where a green alternative where stability is crucial and decay resistance is desired.

What Makes Closed-System Thermal Modification Different?

Using a simple and accurate control strategy, this system keeps the wood near hygroscopic equilibrium during the entire treatment cycle. Also known in the lumber industry as “EMC,” equilibrium moisture content is defined as the point where wood stops absorbing moisture from or releasing moisture into the surrounding air. At this point, the wood is said to have reached hygroscopic equilibrium. For thermally modified wood from a closed system, the resulting wood is at a constant 5% moisture content.

Why is Equilibrium Moisture Content Important?

For anyone working with wood on a regular basis, EMC is important for a number of reasons. Wood expands and contracts with moisture content depending on the average moisture content of the region where the wood is located. When wood is exposed to a wet environment, such as exterior applications, wood will cup, warp, and degrade without specific exterior treatments, such as thermal modification.

How Is a Pressurized Closed System Better for Thermally Modified Wood?

Since the system is closed and pressurized, the system does not allow the wood to go below 5% moisture content. In some other system types, the wood is dried to almost 0% and then reabsorbs moisture after the treatment is completed. The pressurized system doesn’t allow that fluctuation, which reduces the treatment stress on the wood. This allows for a more stable product, and as a result, reduces the potential for cracking and splitting.

The pressurized closed system improves the wood’s properties, resulting in increased dimensional stability and increased decay resistance, while creating a chemical-free wood that repels moisture.

What Species Are Offered in Thermally Modified VikingWood?

VikingWood thermally modified lumber is offered in poplar, ash, red oak, white oak, soft maple, eastern white pine and southern yellow pine. Other species may be available upon request.