THERMOWOOD HANDBOOK INTERNATIONAL THERMOWOOD ASSOCIATION (ITWA)
THERMOWOOD HANDBOOK INTERNATIONAL THERMOWOOD ASSOCIATION (ITWA)
This handbook by the International Thermowood Association provides detailed information on ThermoWood products and processes, serving as a resource for various stakeholders. It combines theoretical insights, laboratory results, field testing, and practical advice, with regular updates as new data emerges.
Background: The ThermoWood process, developed in Finland, enhances wood stability, insulation, and decay resistance through heat treatment.
Process Overview: It involves three phases: drying, heat treatment, and cooling with moisture conditioning, adaptable for different wood species.
Changes in Wood Structure: Heat treatment alters wood properties, reducing swelling and shrinkage, improving durability, and changing color.
Standard Treatment Classification: ThermoWood is classified into Thermo-S (stability) and Thermo-D (durability) classes.
Quality factors include wood species, timber quality, and moisture content, with specific requirements for raw materials.
The process uses specialized equipment, focusing on energy efficiency and environmental considerations.
Heat treatment results in chemical and physical changes, enhancing durability, weather resistance, and color.
Guidelines cover industrial processing, health, and safety considerations.
Applications include construction and furniture, with maintenance and safety guidelines provided.
Proper practices are essential to maintain quality.
Addresses common inquiries about ThermoWood products and processes.
Lists relevant standards for wood treatment and durability.
Outlines standards and tests for wood durability, ensuring treatment effectiveness against environmental factors.
Details grading systems and quality requirements for commonly used wood species.
Describes the drying, heat treatment, and conditioning phases, emphasizing energy efficiency and environmental friendliness.
Highlights improvements in stability, durability, and resistance to weathering.
Analyzes the effects of heat treatment on wood, focusing on component degradation and physical changes.
- Cellulose and Hemicelluloses: Degrade differently, improving stability.
- Lignin: More heat-resistant, undergoing significant changes above 200°C.
- Extractives: Evaporate easily, contributing to weight loss.
- Density: Reduced due to mass loss.
- Strength: Generally lower, with significant bending strength decrease above 220°C.
- Modulus of Elasticity: Not significantly affected.
- Compression Strength: Improved at higher temperatures.
- Hardness: Slightly increased with higher temperatures.
- Equilibrium Moisture Content: Reduced, enhancing stability.
- Screw Holding Strength: Affected by density variations.
- Impact Bending Strength: Reduced compared to untreated wood.
- Shear and Splitting Strength: Reduced at higher temperatures.
Not recommended for load-bearing applications without further testing.
Heat treatment significantly reduces swelling, maintaining form better than untreated wood.
Lower water permeability compared to kiln-dried wood.
Reduced by 20-25%, suitable for specific applications.
Classified in fire class D, similar to untreated wood.
Shows resistance to decay, with higher temperatures improving resistance.
Resistant to certain insects but not termites.
Retains lower moisture content after exposure, with surface mould growth possible.
Discusses moisture levels and effects of sunlight exposure, recommending UV-protective treatments.
Affects color and surface characteristics, with higher temperatures resulting in darker wood.
Better resistance with appropriate coatings, emphasizing surface treatments.
Guidelines for handling, machining, and gluing, emphasizing sharp tools and dust management.
Minimizing water content in adhesives is crucial, with specific recommendations for different adhesive types.
Recommendations for adhesives and machining, emphasizing pre-planing and adhesive application.
Guidelines for using screws and nails, considering decreased strength.
Comparable to untreated wood, with recommendations for coatings and treatments.
Preliminary tests show good results with fire retardants.
Successful use of heat-treated wood, with recommendations for tools and adhesives.
Emits fewer VOCs, with dust management recommended.
Emphasizes dust management and proper tool use.
Stable for treatment, reducing cracking and flaking.
Recommendations for maintaining color and preventing greying.
Suitable due to hygienic properties, with recommendations for sealing.
Maintenance intervals vary, with recommendations for cleaning and inspection.
Similar to other woods, with recommendations for dust management.
Recommendations for storage and waste treatment.
Addresses common questions about ThermoWood's properties and applications.
Catalog excerpts
nova wood INTERIORS & EXTERIORS THERMOWOOD HANDBOOK INTERNATIONAL THERMOWOOD ASSOCIATION (ITWA)
Open the catalog to page 1
Preface This handbook has been produced by the members of the International Thermowood Association. When new products and methods of production enter the various markets, it is very important to offer as much information as possible concerning the product and process so as to raise and maintain the level of knowledge as efficiently as possible. Therefore, we hope that this handbook will act as a good information source for specifiers, end users in industry, construction companies, timber merchants, etc. The aim of the handbook is to present a good mix between theoretical material, laboratory...
Open the catalog to page 2
CHAPTER 0. Cover page ... 1 - 0 1.2. The ThermoWood® process in brief .1-1 1.3. Changes in wood structure and chemical reactions .3-1 1.4. Standard ThermoWood® treatment classification .. 4 -1 2.1. Factors affecting the quality of heat-treated wood .1-2 2.2. Sawn timber quality .1-2 2.2.1. General Nordic Softwood timber quality 2.2.3. Minimum requirements for raw material 2-2 CHAPTER 3. ThermoWood® process ... 1 - 3 CHAPTER 4. ThermoWood® properties . ..1-4 4.2.4. Equilibrium moisture content 10-4 4.2.5. Swelling and shrinkage due to moisture. 11-4
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CHAPTER 5. Working with ThermoWood® in industrial plants .1-5 5.6. Industrial gluing and jointing 3-5 5.7. Industrial surface treatment ...6 - 5 5.9. Practical experiences from a Finnish 6.5. ThermoWood® in sauna benches .4-6 CHAPTER 7. Handling and storage of ThermoWood® ..1-7 7.2. Handling of residual and discarded products 1-7 CHAPTER 8.Frequently asked questions and answers . ... 1 - 8
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1. Introduction 1.1. Background It has been known for centuries that burning the surface of wood in open fire will make it more durable in exterior use. Even the Vikings used this method in outdoor structures such as fences. Heat treatment of wood was scientifically studied by Stamm and Hansen in the 1930s in Germany and by White in the 1940s in the United States. In the 1950s, Germans Bavendam, Runkel, and Buro continued research into the subject. Kollman and Schneider published their findings in the 1960s, and Rusche and Burmester in the 1970’s. More recently, research work was carried out...
Open the catalog to page 5
ThermoWood® process Figure 1-1. Diagram of the production process When the temperature is raised or lowered, a special adjustment system is used in order to prevent surface and inside splitting and checking. Customised adjustment values are used for different wood species and dimensions. The raw material can be green or kiln-dried wood. If the process is begun with green wood, the wood can be dried in a very fast high-temperature drying process. The method is suitable for softwood and hardwood species. However, the process must be optimised separately for each wood species. For more specific...
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1.3. Changes in wood structure and chemical reactions As a result of the heat treatment process the wood structure is re-formed, the following pictures show how the structure differs between normal untreated pine and heat treated pine. Figure 2-1. Untreated pine Figure 3-1. Heat-treated pine Heating wood permanently changes several of its chemical and physical properties. The change in properties is mainly caused by thermic degrading of hemicelluloses. Desired changes start to appear already at about 150 ºC, and the changes continue as the temperature is increased in stages. As a result, swelling...
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1.4. Standard ThermoWood treatment classification Softwood and hardwood species have a separate classification since their properties clearly differ. There are two classes of heat treatment. Having more than two classes is not reasonable since wood properties change slowly at first as the temperature increases. Once the treatment temperature exceeds 200 oC, the properties change rapidly. Using more than two classes would generate a risk of mixing properties of different classes. 215 oC is sufficient as a maximum temperature value yet is not so high that the effects of heat treatment on the wood’s...
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Recommended end use applications for Thermo-D class heat-treated timber: Thermo-D Softwood - cladding - outer doors - shutters - environmental constructions - sauna and bathroom furnishing - flooring - garden furniture Thermo-D Hardwood End use applications as in Thermo-S. If a darker colour is desired, Thermo-D should be used. Summary of the effects of the ThermoWood process on wood properties, by treatment class Softwoods (pine and spruce) Thermo-S Treatment temperature Weather resistance Dimensional stability Bending strength Colour darkness Hardwoods (birch and aspen) Thermo-S Treatment temperature...
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Wood preservatives. Determination of the protective effectiveness against Lyctus Brunneus (Stephens). Part 1: Application by surface treatment (laboratory method) Wood preservatives. Determination of the toxic values against Anobium punctatum (De Geer) by larval transfer (Laboratory method) Wood preservatives. Determination of the preventive action against recently hatched larvae of Hylotrupes bajulus (Linnaeus) (Laboratory method) Wood preservatives. Determination of the toxic values against Hylotrupes bajulus (Linnaeus) larvae (Laboratory method) Wood preservatives. Accelerated ageing of treated...
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Paints and varnishes. Coating materials and coating systems for exterior wood. Part 3: Natural weathering test EN 927 – 4 Paints and varnishes. Coating materials and coating systems for exterior wood. Part 4: Assessment of the water-vapour permeability EN 927 – 5 Paints and varnishes. Coating materials and coating systems for exterior wood. Part 5: Assessment of the liquid water permeability EN 12037 Wood preservatives - Field test method for determining the relative protective effectiveness of a wood preservative exposed out of ground contact - Horizontal lap-joint method ISO 5660 – 1 Fire tests;...
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2. Raw material 2.1. Factors affecting the quality of heat-treated wood 2.1.1. General The quality of raw material has a significant effect on the quality of the final heat-treated wood product. In principle, all wood species can be heat-treated. However, the parameters used for the process must be optimised separately for each wood species. 2.1.2. Wood species In Finland, the species used for heat treatment are pine (Pinus sylvestris), spruce (Picea abies), birch (Betula pendula), and aspen (Populus tremula). In addition, some experience has been gained in the treatment of Radiata pine (Pinus...
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