Effect of damage to polyurea coatings on metal losses from ammoniacal copper zinc arsenate treated Douglas-fir pile sections

IRG/WP 19-40867

M J Konkler, J J Morrell

Metal-based preservatives remain the most widely used treatments for protecting wood in soil or water contact. While these treatments are highly effective, one drawback is a tendency for small amounts of metal to migrate into the surrounding environment. The greatest risk in this regard is copper because many organisms are highly sensitive to this metal. While post treatment practices can reduce migration risk, even these small amounts can be problematic in some applications. Coatings have long been used to prolong the useful life of various products and could be useful for preservative treated products used in aquatic applications. We assessed the potential for a polyurea coating to reduce the potential for preservative migration in saltwater immersion, then progressively damaged the coating to expose increasing percentages of formerly coated wood. The polyurea coating completely eliminated metal losses from the wood. Removing increasing amounts of polyurea resulted in increases in metal losses over time. My results demonstrate that coatings can largely eliminate the risk of preservative migration, but they must be maintained to avoid excessive metal migration.

Keywords: ammoniacal copper zinc arsenate, best management practices, polyurea coatings, Douglas-fir, copper toxicity

Conference: 19-05-12/16 Quebec City, Canada

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