This durable and environmentally friendly cladding and decking is ideally suited to Australian conditions.

Australia’s harsh environment and voracious insect life means most of the timbers in our market are either chemically treated or naturally highly durable. The former category of products often comes with concerns regarding disposal, and the latter is often from old-growth forests, which may come with sustainability concerns. Which is why it’s good to see a new thermally modified wood brand enter the fray.

Thermally modified wood is produced using chemical-free heat treatment, with no addition of pesticides or fungicides at any stage of the process. While the basic idea has been around for a long time, the Technical Research Institute of Finland developed a sophisticated process that is suitable for both hardwoods and softwoods – allowing a range of sustainable timbers to be used.

This technology has been perfected in the product range from Estonian company Thermory, the leading international supplier of thermally modified wood products for exterior and interior uses. Their product is now available from local suppliers InStyle Timber Products and Australian Timbers.

The process is seemingly simple, but highly effective. Timber is slowly heated in special kilns to approximately 215°C, while controlling the moisture content through means of steam. Under the influence of these high temperatures, the chemical and physical properties of wood undergo permanent change, with every fibre modified. The end phase of the process is cooling down and re-moisturising the timber to the normal equilibrium moisture content, suitable for machining, installing and using.

Thermo-treatment changes wood’s chemical composition. The depolymerisation of lignin under the influence of high temperature reduces the length of the wood’s natural chains of cellulose, so most of the wood sugars are cooked out, eliminating the food source for bacteria and insects.

The side effect of this process is a change in the colour of the wood through the entire thickness of each piece. The colour becomes more saturated and homogeneous, emphasising the natural grain and increasing the aesthetic quality of the timber. The large batch sizes possible in the specialist kilns allow for consistency across an end-user’s project and can be tailored to optimise results for a particular timber.

More than just an attractive appearance, the main effect of thermal modification is a significant increase in biological durability. Thermo-treated wood does not require any chemical protection from rot: bio-damaging agents are destroyed and the treated product has significantly lowered moisture absorbency. According to Thermory’s rigorous external tests, thermally modified hardwoods (e.g. American and European ash) gain durability class 1 (over 25 years’ service life outdoors), and thermally modified softwoods (e.g. Scots pine and radiata) have class 2, which means 15-25 years of carefree lifespan outdoors.

These qualities have seen Thermory timbers replace tropical hardwoods in much of the outdoor timber products market. Not only does thermally modified wood match tropical hardwoods in durability, it outplays them in sustainability and dimensional stability. Equilibrium moisture content of Thermory wood is reduced 50% compared to untreated wood, and this difference remains after years of exposure.

Swelling and shrinkage of wood strongly depend on the absorptive qualities of the wood and for Thermory wood it is reduced 5-10 times for hardwoods and 2-3 times for softwoods. Thanks to its high resistance to heat and moisture, Thermory is long-lasting in applications where timber can fail – around pool areas, at waterfronts and in rooms with high humidity.

Left untreated, the timbers will fade naturally, or a UV protectant oil will preserve the natural colour (the products take coatings well). In addition to being highly durable, the low equilibrium moisture content decreases thermal conductivity, so a Thermory deck will always be cooler on hot summer days than any other deck.

The Thermory range is now coming into Australia, with a selection of popular timbers including ash, spruce and pine, available as cladding and decking in a range of colours and finishes. One of the most exciting cladding products is Ignite, which delivers a shou sugi ban (charred) look without smudging onto the clothes of passers-by, while Drift gives a recycled timber look. Decking products come with a set of easy and adaptable installation options you can select from according to your need.

Products are also suitable for interiors. The removal of resins and formaldehydes and zero chemical content makes Thermory ideal for applications with sensitive environmental concerns, such as family homes, schools and various care facilities.

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Image: The thermal process makes the timber colour richer and more consistent, and highlights the beauty of its natural grain.