Exposure of CCA and ACZA treated parallel strand lumber to marine borer attack in northeastern and southeastern waters of the United States of America

IRG/WP 06-30400

B Goodell, P Merrick, J Jellison, Y Qian

Southern pine and Douglas fir Parallel Strand Lumber (PSL) panels were treated with chromated copper arsenate (CCA) or ammoniacal copper zinc arsenate (ACZA), respectively and exposed in a marine environment in Massachusetts (northeastern USA coast) for 7 years. Similarly treated panels were also exposed to a site on the Atlantic coast Florida (southeastern USA) for the same period. In the northern site, untreated PSL was also tested and performed well in comparison to untreated solid pine wood and displayed no delamination. Treatment with 16 kg/m3 (1 lb./ft3) or greater of either wood preservative provided adequate protection of the panels. ACZA treated samples displayed significant mass losses over the 7-year exposure period even though no marine borer attack of the higher retention samples occurred. Internal and external evaluation of the samples after 7 years indicated that external evaluation accurately estimated the conditions inside the samples when limited degradation was present. However, as degradation progressed, the data suggest that internal degradation may be more extensive than indicated by the external ratings, at least when shipworm damage was most prevalent. In the Florida site, extensive degradation of control panels and panels treated to lower preservative retention was observed, but PSL panels treated to higher retentions performed well. Overall, the PSL panels when treated with appropriate levels of preservative performed very well in the marine environment.

Keywords: parallel strand lumber, CCA, ACZA, marine borers, gribble, shipworms, degradation

Conference: 06-06-18/22 Tromsoe, Norway

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