Modified momentum

19 April 2014

The market’s light bulb moment for the potential of thermally-modified US hardwood is just around the corner, writes Neil Summers of Timber Dimension, which is working with the American Hardwood Export Council to test and validate the material’s performance.

Thermal modification to alter the properties of timber, making it more suited to outdoor use, was previously the domain of softwoods, but it's now being applied increasingly to North American hardwoods too.

Small innovative projects supported by the American Hardwood Export Council (AHEC), like the US tulipwood Infinity bench designed by Martin Gamper, have already demonstrated how the process can be used to great effect. And, while there's always a degree of scepticism and uncertainty over the performance of anything new, I now believe the 'light bulb' project highlighting its value is just around the corner.

The focus of Timber Dimension's work with AHEC this year is on helping dispel remaining doubts, with a range of testing programmes planned so specifiers can be confident that thermally-modified US hardwoods will meet highest performance expectations.

Durability and strength
We have already established the issue of durability, which is key to the longevity of a species used externally. Independent testing at CATAS laboratories in Italy showed that a durability rating of class 1 (very durable) can be achieved for ash, tulipwood, red oak and soft maple when processed at 212°C.

Initial coating trials with Teknos also show that a thermally-treated substrate provides a dimensionally stable surface for coatings and more work will be done this year to confirm these findings. Leading supplier of penetrating oils, Owatrol, will also conduct exploratory trials with the material.

We also know that thermally-modified tulipwood can be successfully engineered into laminated sections with the use of MUF and PU glues, making it an ideal material for high quality window scantlings. At the Fensterbau exhibition in Germany, several manufacturers expressed interest in using the product.

Testing is also on the agenda to confirm thermally-treated hardwoods' strength properties and how the treatment process reduces bending strength. Evidence suggests around 20%, but this is not species specific.

There are many examples of high quality thermally-modified timber flooring on the market too, demonstrating how the process improves hardness properties, and our aim is also to evaluate this.

Market acceptance is further underlined by Howarth Timber deciding this year to stock and promote thermally-modified ash cladding and decking, a move which group marketing and product manager Neale Brewster said was designed not only to provide the customer with something that performed, but that would also satisfy their desire for products that stood out.

AHEC has also joined the Timber Decking and Cladding Association to widen knowledge of US thermally-modified hardwoods for this type of application, and to play an active role in the organisation.

And for anyone wishing to know more about the product and its markets, the eighth Thermally Modified Timber workshop takes place in Dresden from May 22-23. For more details go to

Thermally-modified tulipwood - Take 11
The American Hardwood Export Council's project to highlight the durability, versatility and aesthetics of thermally-modified tulipwood has more than proved its point.

The initiative started at design magazine Wallpaper's Workspace Exhibition last year, where the striking Octopus structure, designed by architect Adam Khan and fabricated by joiner/maker Adam Kershaw, formed the backdrop for different home-workplace concepts.

They used a blend of light, unprocessed tulipwood and the dark heat-treated material to demonstrate its looks, machining and manufacturing properties. Their creation went on to tour Europe, forming an exhibition stand in various configurations, latterly at Ecobuild in London in March, where it provided the set for the Wood Awards display.

Then, in its most dramatic reinvention yet, the Octopus was totally remodelled, with the wide boards cut down to slats, to form the juice bar for Wallpaper's Handmade show, held as part of the Milan Design Week earlier this month.

The exercise has won over yet another architect to the possibilities of heat-treated US hardwood in London-based Carl Turner, who designed the bar and worked with Adam Kershaw to create it.

"We were approached by Wallpaper to create something for Handmade and were introduced to AHEC to choose the material," said Mr Turner. "We liked their previous showcase projects with designers and we also enjoy working with wood, plus the idea to recycle the Octopus appealed to our environmental ethos."

The design idea, he added, was to get away from the traditional concept of a bar as a solid barrier, so the tulipwood slats were glued and slotted together in an open frame.

"We also mixed natural and heat-treated to create a camouflage effect, and used heat-treated exclusively for the bar top as it's stain resistant," said Mr Turner. "The timber worked beautifully and oiled up well." His practice, he added, would now put tulipwood in its portfolio for future projects.

"We also designed the bar in a modular format so it could be turned into other objects," he said.

"So hopefully the tulipwood will get another 11 outings."

Gamper bench in treated red oak, soft maple, ash, yellow birch and tulipwood
The Octopus structure at Ecobuild, remodelled as the juice bar for Milan Design Week
The Octopus structure at Ecobuild