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Use sharp tools
As the heat treatment makes the wood more brittle, we recommend the use of sharp tools when working with the wood. We also recommend that one always pre-drill when using screws or nails close to the edges to avoid cracking.
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Rust free nails and screws
Thermowood has a slightly lower pH value than untreated wood which can lead to discolouration. To avoid this we recommend the use of rust free nails and screws such as stainless steel.
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Gluing
Tests from using glue on Thermowood show that it can be used in the same way as on any other type of wood with the exception of PVA glue. As this glue is water based it requires a much longer pressing and curing process. When using PU glue it is necessary to use extra amounts of water as Thermowood has lower moisture levels than other wood.
Strength
The strength and solidity are lower in heat treated wood which is why it is not suitable for constructions requiring a certain stress grade in the wood.
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Resistance
The biological resistance to degradation, also known as the natural resistance, varies enormously between different types of wood. Because of this there are three standards used in classifying wood. EN 350-1 is of particular interest as it shows the natural resistance of the heartwood in hundreds of commercially interesting types of wood.
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|
Class 1 |
Class 2 |
Class 3 |
Class 4 |
Class 5 |
|
Teak |
Western Red Ceder |
Siberian larch |
European larch |
Ash |
|
Merbau |
European Oak |
Douglas Fir |
Spruce |
Beech |
|
Jarrah |
Thermowood® |
Walnut |
Pine |
Maple |
Source: Luleå Technical University
The table above only includes wood free from chemicals. Pressure impregnated wood uses other classifications developed by the Nordic wood preservation council (NTR – Nordiska TräskyddsRådet). When comparing pressure impregnated wood and Thermowood it has been noted that Thermowood has the same or even better resitance.
