Improving the service life of UK-grown softwoods for commercial applications is often seen as the Holy Grail – particularly when it’s for applications such as ground contact use. Preservative treated spruce is used extensively in the UK but there have been concerns about its service life in safety critical ground contact (Use Class 4) applications.
Against this background, a joint TRADA and BRE research project into the natural durability of the heartwood of commercially important softwood species from different geographic regions of the UK has just been completed. Evaluation of the data is in progress, with final results due in the summer.
The study investigated if geographic origin could influence natural durability and if the information could be used to predict the service life of incised timber. Incising (making slits or pinholes in the timber surface) is not currently widespread in the UK, largely because the benefits have not yet been shown to justify the initial outlay on equipment.
Incising is sometimes criticised for reducing the strength of timber, but this strength loss is not believed to be significant for many end uses and the increased preservative penetration can extend service life to a degree that far outweighs the initial loss of strength.
Baseline data will be used to help evaluate and quantify improvements in service life performance provided by incising and pressure treatment.
It is hoped that, by researching this particular area, it will be possible to more accurately predict service life of timber products and possibly underpin greater confidence in extending service life predictions of incised timber in Use Class 4 service conditions.
"A better understanding of the natural durability of UK softwoods from laboratory tests, connected to the ambition of the Wood Protection Association (WPA) field trial of incised posts, will enable more accurate performance classification of treated UK softwoods in ground contact," said Dr Ed Suttie, director of BRE Timber.
"This will provide a solid foundation of evidence for confidently translating into service life predictions for the incised timber product in Use Class 4 applications."
The research was based on laboratory-based EN 113 trials to determine provisional natural durability ratings. The trial focused on three refractory timber species, whitewood, Douglas fir and hybrid larch, taken from five different geographic regions – Scotland (east and west), Wales and England (north-east and south-west).
TRADA and BRE plan to compare data from this EN 113 trial with data from the forthcoming full-scale field trials of incised UK softwood being proposed by the WPA.
Commenting on the research, Dr John Williams of TRADA Technology, said: "TRADA and BRE share a common desire to encourage the wider and appropriate use of UK-grown softwoods, particularly where added value can be generated.
"The practice of incising prior to preservative treatment for Use Class 4 is already starting to open up new markets for UK softwoods, providing a reliable product for the customer," he said. "This is a huge opportunity for UK grown softwood products. Moreover, this work can form the foundation for less reliance on imported products. The UK needs to find value added uses for this timber. A process that can demonstrate compliance for Use Class 4 provides an opportunity for wider uptake and consumption of UK timber resources."
The research outcomes are predicted to help ensure UK timber can become the material of choice for applications where comparatively high levels of treatment for ground contact are required and to enhance confidence in the use of preservative treated timber in safety critical ground contact applications.
