The Thermal Wood Process

The thermal modification of wood is a Finnish technology that has been used successfully in Europe for about 15 years.    It is a proven technology.   Vikings used the heating of wood to help waterproof their boats.   Native Americans used heating to harden their arrows.   The concept is not new, with increased technology it is now practical to produce TMW on a consistent and commercial scale.

Thermally Modified Wood

Thermal modification of wood involves heating wood to a high temperature while at the same time protecting it with steam.    The process uses heat and water vapour to produce environmentally-friendly modified wood products.   These products are free of any impregnation substances.Thermal modification impacts several wood properties and changes them permanently.

  • The dimensional stability of wood significantly improves in conditions where the moisture level varies.
  • Thermal insulation properties of thermal wood are superior to those of non-treated wood.
  • The effect of thermal modification is such that wood becomes decay-resistant.
  • Thermal modification does cause a slight reduction in the strength properties of wood.
  • Thermal modification can be applied to the wood of nearly all tree species.

Stellac® kiln technology

Thermally Modified Wood

  • decay- and fungus-resistant for long-term outdoor exposure
  • superior dimensional stability for better-performing joinery and flooring
  • darker colors with improved homogeneity throughout the timber, to substitute exotic species
  • minimized resin, for ease of maintenance and finishing
  • 100% free from chemicals, environment-friendly

Superior decay resistance

We use Stellac® kiln technology to produce the thermally modified wood.  In classifying Stellac® Thermally Modified Wood (TMW), they have taken as guidelines the European Standards covering natural durability.   In short, this mean that the Stellac® process improves decay resistance by decreasing moisture content and minimizing the nutritive sources for decay and fungi.    As a result, Stellac® is the only company that is able to thermally modify the timber to fulfill the criteria defined in the EU standards relating to natural durability.

The timber processed by Stellac® technology has 5 classifications: T5 (lower level – 190 C), T4, D3, D2 and D1 (higher level – 250 C) where for instance, thermally modified spuce and pine in classes D2 and D1 fulfill the criteria defined the EU standard’s for hazard classes 4 and 5.

With Stellac’s® precise and unique process control system, you will enjoy a high level of flexibility and produce products that meet the highest of requirements and expectations when it comes to durability.

Durability tests made with Spruce (Picea abies) and Pine (Pinus Sylvesteris) show that untreated wood loses its mass by 70% where Stellac® Modified Wood at D2 level loses its mass only 5%.   At D1 level, wood processed with Stellac technolgy remains 100% intact.

Matching colors with your needs

Stellac® enables you to achieve a wide range of color tones using a single wood species.   With Stellac’s precise process control system, you will enjoy a proven homogeneity of colors within each kiln load; meeting your highest quality requirements, load after load.

No more resin-related issues

Wood resin is dried out during the Stellac® process, giving you an excellent base for further processing, such as coating.

100% free from chemicals

The Stellac® process uses no chemicals, all the wood produced is 100% wood, no additives, chemicals or other substances.

The Stellac Thermal Wood Modification technology consists of a 5-step process.

During each stage, your raw material is monitored and protected, and the fully automated process control system ensures that the end-product meets your requirements and expectations: high-quality products, maximized yield and consistency of color.

Preparation.

During the Initial Heating(1) and Preconditioning & Drying(2) phases, Stellac brings the temperature above water boiling point, preparing your wood for Thermal Modification. To ensure successful results without defects such as checks, your wood is dried in a gentle and accurately controlled environment.

Modifying your wood.

As your wood has been relaxed by eliminating internal stresses during the Preconditioning & Drying phase, we are now ready for Thermal Modification(3). Depending on the final application and your requirements, the kiln temperature will be raised to up to 250 C (482 F)

Relaxation.

As your wood has been exposed to harsh temperatures, it needs to be relaxed carefully in order to avoid splitting and other defects. During the Conditioning(4) phase, the correct moisture level is restored, appropriate to the final application of the wood. Before being removed and further processed, the timber is taken through the gentle Cool Down(5) phase, in order to ensure a long-lasting, high-quality end product.