Premature failure of treated timber in wharfs in Papua New Guinea, attributed to defects in design
S M Cragg
The performance of timber in wharfs in Papua New Guinea has been monitored for a number of years. Premature failure of wharf structures was found in many cases to be due to defects in design rather than ineffective preservative treatment. Above-water timbers were found to be prone to severe checking followed by decay. Protection for the end grain of pile tops and the limiting of radial checking in them was found to be vital. Removable metal caps and stout metal bands sized to give a snug fit around the circumference of the pile were found to give the best protection. Major areas of decay or marine borer attack were most common where other structures were attached to the piles in such a fashion that the "envelope" of treated sapwood was breached. In order for treated timber to perform satisfactorily in wharfs, care has to be taken at the design stage. Any post-treatment machining should be undertaken with suitable tools and remedial treatment or protective measures will be required. A list of recommendations for the use of treated timber in wharfs in the tropics is given, relating to the preparation of wood, the construction of the wharf and the protection of vulnerable parts of the installed wharf. The question of good and bad design, and its effect on service life of wharf timbers requires further investigation. The author requests colleagues with information relating to this to contact him.