There’s not much that any of us can do about strong sterling and cheap imports of Baltic and Scandinavian timber. But there is something we can do about another of our key challenges: finding new markets for our home-grown timber. Traditionally the bulk of home-grown timber is sold to the construction industry rather than the higher-value joinery markets. However, a recent study has shown how advances in technology might allow us to address some of these issues and produce a product that could be attractive to the joinery industry.

The study was commissioned by Scottish Enterprise and the Forestry Commission on behalf of the Scottish Forest Industries Cluster, an industry initiative set up to increase the value of forestry to the Scottish economy (TTJ January 26). They asked researchers from the Centre for Timber Technology and Construction at BRE to look at sitka spruce logs, boards and battens from mills in Scotland and to assess the feasibility of re-engineering them for use in joinery products.

Suitable material

Researchers sorted material according to growth rate and found that between one- and two-thirds of material would meet current BS joinery standards with respect to growth rate. Excluding butt logs would significantly increase this percentage. The exercise was carried out manually but suitable scanning technology could potentially be used to automate this process.

The next step involves removing knots, also known as defect cutting. Choices need to be made as to what sizes of knot can be tolerated and whether knots on edges should be removed. The BRE team mapped the knot patterns on falling boards and battens and used a computer model to calculate how much knot-free timber could be recovered by defect cutting for a range of different specifications. Recovery rates ranged from 55-90%, depending on the specification, however, a realistic scenario of removing all edge knots and face knots larger than 10mm diameter produced recovery rates of 70-80%. Knot selection can be carried out automatically by computer scanning using commercially available technology.

Following defect cutting, sections of board or batten can be reassembled by finger-jointing using green gluing.

Laminating technology

Once dried, boards can be planed and laminated to the required final specification. Laminating technology means that lower grade knotty falling board material can be used for internal sections, further increasing recovery rates.

Previous research on coatings for joinery has focused on Norway spruce rather than sitka. This has shown that spruce is more resistant to water absorption than pine. Although this makes preservative treatment more difficult it means that, if the preservative barrier is breached, spruce is more resistant to water penetration.

In the late 1980s and early 90s, JELD-WEN UK Ltd researched the use of Norway spruce in window manufacture and found little difference in product performance from pine. They found several differences in the raw material such as longer fibres, greater levels of abrasion and harder knots, which necessitated changes to the settings of blocks and cutters. However, these were far from insurmountable and, by the early 90s they were making several thousand spruce windows per week. In doing so, they were following the example of the Germans and Dutch who make significant use of whitewood in their joinery products.

Next step

In November last year, a group of Scottish sawmillers met joinery manufacturers and BRE researchers to discuss the findings of the study and to consider how best to take things forward.

Two main sets of questions were identified. The first was the need to assess the levels of investment that would be required for re-engineering and to compare these with potential price premiums. The second focused on the need to build and test products made from Scottish sitka spruce. Mills agreed to supply material for the manufacture of windows that BRE will then test.

It is amazing that, until now, there has been almost no contact between the UK’s sawmilling and joinery sectors. This project is an excellent example of what the Scottish Forest Industries Cluster is about – encouraging different sections of the timber industry to work together for their mutual benefit. The prospect of good quality joinery products from home-grown timber is an exciting one. Watch this space.