The objective of this research was to examine the LOSP treatment options available for H3 exposed glulam of Pinus radiata and P. elliottii. Test specimens were treated before or after gluing with azole LOSP, while some were treated with TBTN or CCA for comparison. They were then exposed at Innisfail or in an Accelerated Field Simulator (AFS) designed to give severe exposure and accelerated results. After 3.1–3.2 years, test specimens were given a performance rating from a scale of 8 (sound) to 0 (destroyed by decay).
The results suggest that treating glulam before gluing will generally give better performance than treatment after gluing.
Decay was more rapid in vertically exposed than horizontally exposed specimens, suggesting that glulam posts need special attention to prevent water penetration. End grain sealants based on copper naphthenate or zinc naphthenate gave improved decay resistance, but on their own were insufficient for post end protection. This suggests that a better approach would be to include barriers (caps) as well, or to use designs where the end is not exposed to rain or can drain away readily.
Glulam manufactured from laminating stock of three species pre-treated with ACQ-D or CA was exposed outdoors in an above-ground field test using a modified post and rail test design. After six years’ exposure, early to moderate decay was found in untreated test units, while those which were preservative-treated were completely sound.