ThermoWood For Hot Tubs
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The manufacturing process of ThermoWood is based on the use of high temperature and steam. No chemicals are used in the treatment. The process improves dimensional stability and biological durability of wood. Another improvement is in the insulation properties of the final material, the process leads to a reduction in thermal conductivity. Due to the high treatment temperatures the resin is removed from the wood.
The ThermoWood treatment process is patented and the trademark is owned by the Finnish ThermoWood Association.
The process can be divided into three phases:
1. Temperature increase and kiln drying: The air temperature in the kiln is raised at a rapid speed using heat and steam to a level of around 100 °C, thereafter the temperature is increased steadily to 130 °C and drying takes place. Steam is used as a vapour membrane to prevent cracking of the wood. The steam also facilitates chemical changes taking place in the wood. At the end of this phase the moisture content is reduced to almost zero.
2. Intensive heat treatment: During the intensive heat treatment phase the air and wood temperature is increased to a level of between 185 – 225 °C. The peak temperature depends on the desired end use of the material. When the target level is reached the temperature remains constant for 2 – 3 hours. Steam is used to prevent the wood from burning and cracking and it also continues to influence the chemical changes taking place in the wood.
3. Cooling and moisture conditioning: The temperature is reduced using water spray systems. Conditioning and re-moisturising takes place to bring the wood moisture content to a workable level over 4 percent.