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What is thermowood?
Thermally Modified Wood: A Scientific Analysis
Thermally modified wood, also known as Thermowood, is the result of an advanced process that fundamentally changes the physical and chemical properties of wood. This process, developed by VTT in Finland, provides a scientifically backed method to enhance the durability and stability of wood without the use of chemicals.
For outdoor applications, thermally modified wood offers a unique combination of durability and dimensional stability.
The Thermowood Process: A Scientific Approach
The Thermowood process is divided into three crucial phases:
- High-temperature drying: Heating to 130°C to reduce moisture content to nearly zero.
- Thermal modification: Heating to 180°C (Thermo-S) or 212°C (Thermo-D) for 2-3 hours, during which significant chemical changes occur.
- Cooling and reconditioning: Controlled cooling and moisture regulation to a final moisture content of 4-6%.
This process results in structural changes at the cellular level, leading to improved properties.
Mechanical Properties
The thermal treatment affects the mechanical properties of the wood:
- Modulus of elasticity and strength: Slight decrease in bending and compressive strength due to structural changes.
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Hardness: Increased Brinell hardness:
- Nova-Ash: 30.5 N/mm²
- Nova-Pine: 15 N/mm²
- Nova-Iroko: 40 N/mm²
- Nail and screw holding capacity: Approximately 20% decrease, to be compensated with stainless steel fasteners.
Physical Properties
Thermal modification leads to significant changes in physical properties:
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Density: Varies by wood species:
- Nova-Ash: 595-629 kg/m³
- Nova-Pine: 362-404 kg/m³
- Nova-Iroko: 576-650 kg/m³
- Moisture content: Reduced to 4-6% after treatment, with an equilibrium moisture content of 10-12% at 95% relative humidity.
- Thermal conductivity: 20% reduction, with Nova-Pine achieving a value of 0.099 W/(m K).
Chemical and Biological Properties
The thermal treatment induces significant chemical changes:
- Durability: Increased resistance to fungi and insects due to the breakdown of hemicellulose.
- Emissions: Characteristic odor from volatile organic compounds (VOCs), which are lower than those of untreated wood.
- Fire resistance: Classified "B-s1, d0" according to EN 13501, further improved with fire retardants.
- Color change: Darker due to caramelization of sugars, with natural graying from UV exposure over time.
Applications and Processing
Thermally modified wood is particularly suitable for:
- Facade cladding: Excellent dimensional stability and weather resistance.
- Decking: Ideal for outdoor furniture due to increased durability.
- Saunas: Improved moisture resistance and insulation properties.
- Frames and doors: Reduced warping and improved insulation.
When processing, consider the following:
- Use of sharp tools due to increased hardness.
- Need for pre-drilling when fastening.
- Recommended use of MUF, polyurethane, or epoxy adhesives.
Maintenance and Durability
Thermally modified wood requires minimal maintenance:
- Regular surface treatment can slow graying and extend lifespan.
- Recommended ground clearance of 4-6 cm for decking boards.
- FSC and PEFC certified, sourced from sustainably managed forests.
Conclusion: Scientific Innovation in Wood Modification
Thermally modified wood represents a significant scientific breakthrough in sustainable wood processing. With its unique combination of enhanced durability, dimensional stability, and environmental friendliness, it offers a superior alternative to traditionally treated wood in many applications.
Discover the possibilities of thermally modified wood in our collections:
Experience the scientifically proven benefits of thermally modified wood and create sustainable, high-quality outdoor spaces.