Durability of light organic solvent preservative (LOSP) treatments for softwood glulam

Treatment options for outdoor above-ground (H3) glulam of Pinus radiata and P. elliottii were examined. Beams were treated with azole LOSP to retentions of ∼40 L/m3 or ∼70 L/m3 either before or after gluing. TBTN-LOSP and CCA were included for comparison. Test specimens were exposed for four years outdoors in the wet tropics at Innisfail or in an accelerated field simulator (AFS) in horizontal or vertical orientation. Decay was 2.5 times faster at Innisfail than in the AFS. Glulam treated before gluing generally performed better than glulam treated after gluing, whether vertically or horizontally exposed. One exception was horizontally exposed specimens in the AFS, perhaps as treated wood is not lost upon dressing when treated in final form. Nevertheless, as glulam failure mostly occurs at ends, treatment before gluing provides better protection of individual laminates, especially important when beams are docked to size. End grain protection can be improved by resealing, and copper naphthenate was more effective than zinc naphthenate.

► Softwood glulam was treated with LOSP before or after gluing.
► Glue-bonds inhibited LOSP penetration when treatment occurred after gluing.
►  Glulam treated before gluing was more durable and improved protection for ends.
► Resealing cut ends with copper or zinc naphthenate improved performance.
► Decay was 2.5 times faster in the wet tropics than in an Accelerated Field Simulator.