Ability of polyethylene and polyurea caps to exclude moisture in pole tops

Water is essential for fungal wood decay. Maintaining wood moisture contents below the fibre saturation point limits fungal degradation. Where unachievable, preservative treatments are used, but may become compromised by post-treatment cuts, especially on the top of vertically oriented poles or timber. The application of water-shedding caps is one method to limit moisture entry into the exposed end grain of utility poles. This study evaluated the ability of polyurea and polyethylene caps to prevent moisture ingress into pentachlorophenol-treated Douglas-fir poles over 172 or 210 months, respectively. Water exclusion was assessed by measuring the moisture content in the heartwood portion of increment cores taken directly beneath pole tops over the study period. Inner heartwood moisture contents of non-capped poles were above the point where fungal growth could occur more frequently than in poles capped with either treatment material. Moisture contents were also elevated in some polyurea-capped poles later in the test, suggesting barrier failure. These results illustrate the benefits of pole capping in limiting moisture entry and, by extension, the risk of fungal attack.