Regarding cross-laminated timber (CLT), one of the frequently asked questions is: "How about the glue?" The boards in CLT are glued together by a layer of polyurethane. It does not emit gas, but if it is not there and we have solid wood, so much the better, and there are fewer concerns about health hazards, flammability or end-of-life issues.

We have shown Holz Thoma held together by pins, but Craig Rawlings of Forest Business Network pointed out something completely different to us:

It is welded wood, and researchers from TMI Ltd and the University of Cambridge's Building Innovation Laboratory have developed "a sustainable process that uses linear friction welding to quickly connect wood elements".

TMI is a welding industry association that has been using friction welding in other materials and started to apply it to wood in 2019. They claim that "the process has many potential benefits, including environmental factors, because the connection does not require any other materials to add wood."

This small video shows two small pieces of wood being rubbed together. A few seconds later, there is a plume of smoke and a piece of solid wood. The Cambridge University press release stated: "This technology has the potential not only to be applied to planed/sawn timber, but also to CLT (Cross Laminated Timber)."

According to the press release, Dr. Darshil Shaw from the University of Cambridge likened it to rubbing hands:

Some things may be more difficult to control; it seems that as the fragments get larger, vibration and compression require more energy. In CLT, the circuit boards are placed in layers at 90 degrees to each other; this is essential to make it stable. After asking Dr. Shaw a question, he told Treehugger:

Dr. Shaw also told Treehugger that the process is indeed effective in the 90-degree direction, but "the bonding performance is relatively weaker than in the parallel direction." There are also challenges in obtaining machine time; TWI's welding machines are almost exclusively used in the high-performance aerospace sector. "Therefore, we are breaking new ground with this technology and its application in completely different fields... This brings challenges!

Therefore, it may take a while before we use welding CLT for construction. In the meantime, here is a longer webinar on the process:

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