Stability
Finnforest ThermoWood® is more stable than untreated softwood, being similar to teak. The changes that occur within the timber during heat treatment make it less able to absorb or lose moisture. The equilibrium moisture content is reduced by some 50% which increases its stability. This reduces the potential for twist, warp or cup. Cupping is reduced up to 90% according to testing of Finnforest ThermoWood®.
Durability
The improved durability of Finnforest ThermoWood® makes it an excellent material for exterior products. It has high resistance to most decay fungi.
Finnforest Thermo-D corresponds to class 2 in resistance against decay (EN 113, EN 350-1, EN 350-2) . For the best performance, ThermoWood should be installed in above ground conditions; ThermoWood is recommended to be used in use class 1-3 (EN 335-2:2006).
Although ThermoWood is not resistant to the biological growth of algae on its surface, it does not cause any structural damage as these organisms get their nourishment from the surrounding air. However, in many cases they are considered to be an aesthetic problem. Their growth can be prevented by using surface treatments.
Moisture content
Finnforest ThermoWood® has a moisture content of 6±2% (65%RH) when packed at the manufacturing unit. This level will change according to atmospheric conditions. The equilibrium moisture content is only half of the corresponding value for untreated pine.
Density
The material density of ThermoWood is approximately 10% lower than that of Nordic pine.
Thermal properties and pH level
The thermal conductivity of Finnforest ThermoWood® is reduced by 20-25% compared with normal softwoods. The pH level of ThermoWood is slightly decreased when compared to untreated wood.
Emissions
ThermoWood has a characteristic odour, which is caused by changes that occur during heat treatment. Although the products have a characteristic odour, no harmful compounds are released into the air. The Total Volatile Organic Compounds (TVOC) values are significantly lower than those for untreated softwoods due to the evaporation of most of the terpenes during the heat treatment process.
Colour
The colour is similar to some tropical hardwood species. The colour of Finnforest ThermoWood® is based on the treatment temperature, which is constantly monitored during production. When ThermoWood is exposed to UV light, it will lose its colour and turn silver grey unless protected by a pigmented surface protection.
Resin-free
Heat treatment removes resin from the timber. As a result, there is no resin leakage or ‘bleed’ through the surface coatings. This combined effect with improved stability can mean reduced maintenance.
Strength
The strength properties decrease during the heat treatment process. The ‘flat-wise’ bending properties of Finnforest Thermowood® can be regarded to be similar to the C16 strength grade structural timber defined in EN 338. Since the influence of knots is more significant in thermally modified wood than in untreated wood, it is safer to use the C14 level values for edgewise use in light structural applications (Helsinki University of Technology HUT statement, 2005). This information applies only to Finnforest ThermoWood® products and quality specifications. This information is not valid for other manufacturers’ products. ThermoWood is not recommended to be used in load-bearing structures.