Thermowood, also known as thermally modified wood, is a remarkable and innovative material that undergoes a specialized heat treatment process to improve its properties and performance.
One of the main advantages of thermo-wood is its improved geometric and dimensional stability. The heat treatment process alters the cell structure of the wood, reducing the moisture content and minimizing the wood’s natural tendency to shrink, swell, warp or crack when exposed to changes in humidity or temperature. This improved stability ensures that the thermowood retains its shape and dimensions over time, making it very suitable for outdoor applications where exposure to weather is an issue.
Shows increased resistance to decay and pest attack. Heat treatment changes the chemical composition of the wood, making it less attractive to insects and fungi that normally cause deterioration in untreated wood This increased durability and resistance to biodegradation make it an ideal choice for exterior decking, cladding, fencing and other outdoor applications where long-lasting durability and protection against decay are critical.
In addition, thermowood has improved thermal insulation properties. The heat treatment process significantly reduces the thermal conductivity of the wood, resulting in a material that, due to the reduced moisture content, provides relatively better insulation than untreated wood or other conventional building materials. This characteristic makes thermowood an excellent choice for applications that require energy efficiency, such as exterior cladding, interior paneling or flooring, which contributes to reduced heating and cooling costs in buildings.
It is important to bear in mind that thermowood is not currently used in statically and dynamically loaded structures due to the deterioration of structural properties during processing. Reduced strength and potential crushability due to damage to certain components of the cell structure, as well as the lack of a standardized classification of thermowood for structural applications, limit its general acceptance and use in load-bearing construction.
Specification Thermowool
| Areas of application | Furniture, floors, walls and ceiling panels Windows, facades, terraces, saunas, etc. |
| Types of Wood | Pine; Custom: Poplar, Silver Fir, Ash, etc. |
Additional information
Almost any timber is suitable for the production of thermowood, but there is a difference between thermowood and thermowood. The heat treatment of softwood, which is softer to begin with than hardwood, results in some loss of density due to evaporation of volatiles and resin leakage. In this respect, hardwood is less affected by heat treatment.
Different technologies can be used for the production of thermowood (mainly thermopine), where the role of oxygen, temperature and pressure vary:
- High temperature kiln drying: in this process, the wood is placed in a kiln and heated to temperatures ranging from 160 to 250 degrees Celsius. As the temperature rises, the oxygen present in the kiln reacts with the wood and initiates chemical reactions. Controlled heating helps remove moisture from the wood and triggers chemical reactions that change its structure.
- Pressure process: the wood is heated, usually between 180 and 230C, under high pressure, the pressure itself limiting the amount of oxygen available. This combination changes the cell structure of the wood, making it denser and more durable. By limiting the oxygen, the process helps prevent excessive oxidation or burning of the wood, ensuring the desired modifications are made without compromising its structural integrity. Thermally treated wood is ideal for exterior applications such as flooring and cladding where weather resistance is essential
- Steam process: the wood is heated in an atmosphere of steam, which initially softens the natural polymer in the wood cells. In this first step, oxygen is present. During the next dry kiln phase, the oxygen supply is limited or controlled to prevent burning. The controlled oxygen environment helps prevent excessive oxidation and maintains the desired temperature range of 180 to 230 degrees Celsius.
There are also methods of producing thermal wood that do not completely exclude the use of chemicals. For example:
- The Lowry process involves subjecting the wood to a combination of heat and a chemical solution. Here, the wood is first placed in a vacuum chamber and the air is removed to create a vacuum. A chemical solution, usually a mixture of water and a fire retardant or preservative, is then introduced into the chamber. The vacuum helps the wood absorb the chemical solution more efficiently. Once the desired temperature and pressure levels are reached, the wood is kept in this environment for a period to allow sufficient chemical penetration and fixation.
The chemicals used in the Lowry process can vary depending on the desired properties and applications of the treated wood. Fire retardants, such as ammonium phosphate or borates, can be used to improve the fire resistance of the wood. Preservatives, such as copper-based compounds or borates, can be used to improve resistance to decay and insect infestation.
In addition to its functional properties, thermowood offers an attractive aesthetic appearance. The heat treatment process can darken the color of the wood, giving it a rich, warm tone that adds a touch of natural beauty to any space. This unique visual aspect makes thermowood a popular choice for architectural and design applications where a distinctive and elegant look is desired.
The most common choice of timber for this type of heat treatment is Ash (Fraxinus), Pine (Pinus), Poplar (Populus), Spruce (Picea) and Oak (Quercus)