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Standard classification of thermally modified wood

 

The coniferous and broadleaved species have a separate classification. There are two classes of wood treatment. The availability of more than two classes is unreasonable because at the beginning of the treatment and with rising temperature the properties of wood change slowly. And only after the treatment temperature exceeds 200 °C,  the properties can change quickly. The use of more than two classes can cause a risk of mixture of properties of different classes. 215 °C is enough because the maximum value of temperature is not so high to make the impact of the heat treatment and structural properties significant.

The treatment level can be carefully optimized according to the end use because the material supplied to the industrial consumers is thermally modified according to the agreement between the buyer and maker. The wood thermally modified cannot fall under any category according to the standard classification of treatment.

 

 

The wood thermally modified belongs to two standard classes of treatment Thermo-S and Thermo-D.

 

Thermo-S

 

The letter “S” of the word “Thermo-S” means stability. The key property of the end use of the product of this treatment class alongside with the appearance is stability. The average tangent lines of shrinkage and swelling for the thermally modified wood of Thermo-S make 6-8%. The thermally modified wood of Thermo-S is classified as a relatively strong material in accordance with EN 113. Its natural decay resistance meets to the requirements of class 3.

The end uses of the thermally modified wood of Thermo-S are recommended as follows:

 

Thermo-S soft wood Thermo-S hard wood
– structural elements

– treatment in dry conditions

– fixation in dry conditions

– furniture

– garden furniture

– benches for saunas

– door and window components

– treatment

– fixation

– furniture

– flooring

– structures of saunas

– garden furniture

 

Thermo-D

The letter “D” of the word “Thermo-D” means durability. The key property of the end use of the product of this treatment class alongside with the appearance is biological durability. The average tangent lines of shrinkage and swelling for the thermally modified wood of Thermo-D make 5-6%. The thermally modified wood of Thermo-D is classified as a strong material in accordance with EN 113. Its natural decay resistance meets to the requirements of class 2.

 

The end uses of the thermally modified wood of Thermo-D are recommended as follows:

 

Thermo-D soft wood Thermo-D hard wood
– cover

– outside door

– window blind

– ecologic facilities

– furniture for saunas and bedrooms

– flooring

– garden furniture

– treatment

– fixation

– furniture

– flooring

– structures of saunas

– garden furniture
If the darker color is required, it will be better to use Thermo-D.

 

The summary of effects that influence on the properties

of thermally modified wood according to the treatment class

Coniferae (pine and spruce)

Thermo-S Thermo- D
treatment temperature 190 °C 212 °C
resistance to weather conditions + ++
stability of size + ++
strength in bending without changes
darker color + ++

 

Broadleaved (birch and aspen)

Thermo-S Thermo- D
treatment temperature 185 °C 200 °C
resistance to weather conditions without changes +
stability of size + +
strength in bending without changes
darker color + ++