The stages of creating thermowood and its unique properties – from the Vikings to Timbera Group

The ancient Vikings were masters at building wooden ships that could withstand the harsh effects of salty water thanks to their unique methods of wood treatment. Modern thermally modified wood, as we know it today, was developed by the Finns in the 1990s. The Vikings didn’t have modern technology, but they came up with their own thermal treatment methods. One of these involved heating the wood over an open fire, which reduced its moisture content and increased its strength. This allowed them to build ships that could endure salt water and serve them faithfully on long sea voyages.

The ship built around 900 AD still has parts of its wooden hull preserved to this day.

The process of creating thermally modified wood

So, what steps does wood go through before it earns the title of thermowood? These processes completely eliminate the negative effects of the environment.

1. First, the wood is steamed in a special kiln at about 100°C for a long period. Drying continues until all the moisture is removed from the wood.
2. Next, the process uses a natural thermochemical reaction with superheated steam at temperatures of up to 240°C – without adding any chemicals.
3. At these high treatment temperatures (180–240°C), hemicellulose (wood sugars) breaks down. Combined with the low equilibrium moisture level, this removes the conditions needed for fungi and microorganisms to survive – essentially destroying the very cause of biological damage in wood. Polysaccharides decompose, and the resulting thermowood no longer provides nutrition for them.

As a result of molecular changes in the wood structure – mainly from cellulose depolymerization and increased crystallinity – the wood becomes stabilized. Its chemical resistance improves, and dimensional stability is ensured. In other words, thermal modification protects the wood against deformation, such as swelling and shrinking, when exposed to changes in humidity and temperature.

At Timbera Group, we most often work with ash and pine. Ash develops a natural dark tone throughout the material, while pine takes on a warmer, honey-colored shade. Depending on the treatment temperature, the color palette ranges from natural wood tones to deep brown.