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Good-looking wood that won’t rot

Thermally modified wood produced by the Stellac® Process is a sustainable alternative to tropical hardwoods and an ecological friendly alternative to chemically impregnated timber.

The possibility of using heat to improve wood’s capacity to resist decay has been known for thousands of years, and has been scientifically investigated since the 1920s. It was not until around 10 years ago, however, that a way was found to manage the process. Drawing on this work, Stellac has developed the Stellac® Process for thermally modifying wood on an industrial scale.

The reliability of the system’s equipment and the process itself ensure that every batch of Stellac® Wood meets high quality specifications. By managing the start-up of new plants using the technology, carefully monitoring quality, and training operators, Stellac is able to ensure that the product always meets customers’ expectations.

Chemical-free durability

Stellac® Wood’s excellent resistance to decay makes it an ideal, environmentally compatible alternative to chemically treated timber in applications where wood is exposed to high levels of moisture or comes into contact with the ground or water. The darker colour of Stellac® Wood compared to conventional timber, resulting from the chemical changes triggered by the process, also make it a visually attractive alternative.

Although spruce, pine, birch, and aspen have been most widely used in the Stellac® Process to date, it is suitable for all types of timber.

The process takes from 20 to more than 75 hours, depending on the thickness of the material and the type of wood, and exposes the timber to temperatures of between 200 and 250 °C. During this time, the sugars in the wood are decomposed into compounds that cannot be utilised by fungi, and natural protective agents in the wood are released. These changes are permanent and improve wood’s resistance to rot and mould dramatically, making it easy to achieve the highest Class 1 standard of resistance to fungal attack.

Stellac® Wood makes excellent decking and cladding material.

The process also changes timber’s physical properties, reducing moisture deformation, shrinkage and swelling, and water absorption.

Good for the environment

No toxic substances are used in the Stellac® Process, making the production, use, and disposal of Stellac® Wood environmentally benign and keeping the exposure levels of people working with the process to a minimum. Thermally modified wood can be disposed of in exactly the same way as untreated timber.

Stellac® Wood is manufactured using only timber certified under the Pan European Forest Certification Scheme (PEFC) from stands that are managed according to ecologically, economically, and social sustainable principles. In addition to using only PEFC-certified timber, the Stellac® Process also only uses energy generated according to agreed green principles.

A full range

Five grades of Stellac® Wood are available. The premium grades, covering timber that has been processed the longest, are designed for applications where the highest levels of decay and weather resistance are a priority, typically outdoors. The other grades are suitable for applications that call for medium resistance to moisture-related deformation and particular colours. Whatever the grade, Stellac® Wood can be worked and finished just like untreated wood.

The most common applications for Stellac® Wood are cladding, siding, decking, playground and garden furniture, window frames, doors, noise barriers, and jetties and pontoons.

Thermally modified wood can also be used inside – in parquet, wall panels, kitchen units, and sauna interiors. Stellac® Wood makes a good material for everyday furniture, accessories, and decorative goods, and has even found application in musical instruments and boats.

Perhaps the best-known public building featuring Stellac® Wood has been the Finnish pavilion at the Expo 2000 World Fair in Hannover.

The right process

Stellac supplies thermal modification units tailored to customers’ specific needs. Units or combinations of units are available with an annual capacity ranging from 1,000 m3 to 50,000 m3 or more.

Stellac® process systems are available for processing both fresh sawn goods and naturally dried or kiln-dried timber. PC-based software monitors and controls the various stages of the process to ensure that timber has precisely the required final moisture content.

Twelve years of direct contact with the ground have not affected this section of Stellac® Wood at all. The Stellac® Process improves wood’s resistance to decay, as well as its dimensional stability, water absorption, shrinkage, and swelling. Its surface hardness and heat insulation properties are also enhanced.
> Seppo Paavilainen
(Published in HighTech Finland 2008)