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LOSP for glulam, when should the treatment be applied?
2011 - IRG/WP 11-30555
Treatment options for outdoor above-ground (H3) exposed glulam of Pinus radiata and P. elliottii were examined. Beams were treated with azole LOSP (containing a zinc tracer) aiming for retentions of 35-40 l/m3 or 70-80 l/m3. Treatment was conducted either before or after gluing. TBTN LOSP and CCA were included as comparative treatments. Test specimens for exposure were cut after treatment, while wafers were also cut for spot testing. Penetration was examined using PAN indicator, with best results for TBTN-treated P. elliottii where image analysis showed 67% mean penetration. The spot test for zinc tracer in the azole-treated glulam was generally ineffective with 15% penetration the highest level detected. Test specimens exposed for two years were given a performance rating from 0 to 8 where 0 is failed and 8 sound. Horizontally exposed untreated test specimens at Innisfail were severely decayed, with the mean rating for P. elliottii 0.4 and for P. radiata 1.4. There was less decay in the accelerated field simulator (AFS). For LOSP azole-treated test specimens at Innisfail, only P. radiata treated before gluing was sound. P. radiata treated after gluing had mean ratings of 7.3 (40 l/m3) and 7.8 (69 l/m3). For P. elliottii, specimens treated to the lower retention (35-40 l/m3) before gluing had a mean rating of 7.9 compared to a mean rating of 7.6 (43 l/m3) when treated after gluing. Going against the trend were the higher retentions in P. elliottii with a mean rating of 6.8 (56 l/m3) when treated before gluing compared to a mean rating of 7.9 (82 l/m3) when treated after gluing, probably reflecting retention level differences. Vertically exposed (like posts) treated test specimens often had more decay. The worst performing vertically exposed glulam was usually treated after gluing. End sealing glulam docked after treatment with CuN or ZnN did not necessarily improve performance. The results to date suggest that treating glulam before gluing will generally give better performance than treatment after gluing.
L J Cookson