Ten-Year Performance of Stakes and Decking Treated with Copper Azole Type B and Alkaline Copper Quat Type D (Carbonate)

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Abstract Development of wood preservatives typically involves laboratory tests using mycelial inoculation and field tests with through-treated small-dimension pine sapwood samples. These preservatives are then commercialized for use also on refractory wood species in Canada and the western United States. A field test was established at two locations in Canada to assess performance of stakes and decks of three species, both untreated and treated with a range of retentions of copper azole type B (CA-B), and two species treated with a range of retentions of alkaline copper quaternary carbonate formulation (ACQ-D). The decking was inspected after 10 years of exposure. CA-B– and ACQ-D–treated boards were generally in excellent condition except at preservative retentions well below standard. Decay was extensive in boards without treatment at both test sites. At one test site, decay was also extensive in preservative-treated white spruce at low retention treated without incising and without end coat. The difference in performance between boards with and without end coat illustrated the beneficial effect of end-cut preservative. At the ground-contact retention of 3.3 kg/m3 CA-B, stakes of all three species were predominantly sound after 10 years of exposure at both sites. ACQ-D–treated stakes at retentions around 6.4 kg/m3 were sound at one test site, but some stakes showed slight to moderate decay at the other site. Moderate decay was found at retentions below this. Both preservatives were effective against termite attack, but very severe decay and termite attack were present in untreated control stakes of all three species.