ThermoWood® heat treatment process has been developed and patented by VTT Technical Research Centre of Finland. The process can be divided into three phases: Phase 1 - Temperature increase and high-temperature drying Using heat and steam, the kiln temperature is raised rapidly to a level of around 100 ºC. Thereafter, the temperature is increased steadily to 130 ºC, during which time the high-temperature drying takes place and the moisture content in the wood decreases to nearly zero. Phase 2 - Heat treatment Once high-temperature drying has taken place, the temperature inside the kiln is increased to between 185 ºC and 215 ºC. When the target level has been reached, the temperature remains constant for 2–3 hours depending on the end-use application. Phase 3 - Cooling and moisture conditioning The final stage is to lower the temperature by using water spray systems; when the temperature has reached 80–90 ºC, re-moisturizing takes place to bring the wood moisture content to a useable level, 4–7%. Key Properties: 1. Density. The ThermoWood process reduces the density of wood by about 10 % on average. 2. Strength Generally the strength of wood has directly related to its density. The ThermoWood process slightly lowers the density of wood and therefore will somewhat effect the strength as well, but weight-strength-value can be practically unchanged. Bending strength Material treated at temperatures below 200 °C does not experience a significant loss in bending strength. A clear reduction in horizontal bending strength can be found in material treated at temperatures above 200 °C. At this stage it is recommended that ThermoWood is not to be used for horizontal load bearing structural usage. Compression strength The Compression strength is mainly dependent on the actual density of wood. According to tests it is has been found that the ThermoWood process has no significant effect on the compression strength values. Splitting strength The ThermoWood process can cause some reduction in the splitting strength depending on treatment temperature, the reduction increases as the temperature goes over 200 °C. Screw holding strength The screw holding strength has a strongly related to density. The screw holding strength is mainly affected by the varying densities of different wood species rather than from the ThermoWood process. It was found that material with a lower density has better results when narrower pre-drilled holes are used. 3. Surface Hardness The ThermoWood process has limited effects on the Brinell hardness properties, variance is more related to the density and the wood species being used. 4. Equilibrium moisture content The ThermoWood process leads to a reduction in equilibrium moisture content. When treated at the highest temperatures the equilibrium moisture content can be 40-50 percent lower compared to untreated wood. 5. Stability Because of lower equilibrium moisture content and the changes in the chemical composition of the wood, the chance of this wood warping, shrinking or expanding will be significantly reduced. In some cases the reduction in dimensional movement can be as much as 40-50%. 6. Permeability The ThermoWood process reduces the water uptake of wood; the levels may differ depending on the original wood species. 7. Thermal properties The tests have shown that the thermal conductivity of ThermoWood is 20 - 25 percent lower compared to untreated wood, thus giving improved insulation performance. 8. Biological durability Standard tests (EN 113, ENV 807) made in laboratory conditions have proven a significant improvement in biological durability. Improvements in biological durability are a result of the removal of natural food sources in the wood and also changes in the chemical and structural composition. Levels of resistance to fungal decay increase as higher temperatures are used. ThermoWood is recommended to be used in hazard classes 1 to 3 in accordance with EN-335-1 without the need for any further chemical protection. The treatment is throughout the wood piece and is not subject to leaching problems. 9. Weather resistance As with most materials, ThermoWood is unable to resist the effects of ultra violet radiation. As a result, over a fairly short period of time when exposed to direct sunlight, the colour changes from the original brown appearance to a grey weathered colour, although the original colour can be brought back by sanding. In addition the ultra violet radiation can cause small surface shakes to occur. Natural effects of rain and sun will cause some early wood to be removed from the surface, especially on un-coated boards, this occurs with all wood material over time. It is highly recommended to apply a pigment based surface protection to prevent colour changes and other natural effects of the weather.