Tar-oil uptake vs time in immersion treatment of short pine posts: A simple technique applicable to rural communities of Papua New Guinea
B K Gusamo, R Tulo
Pinus caribaea and Araucaria cunninghamii logs ca. 100 mm in diameter were shortened to lengths 25-30 cm, conditioned to at/below fibre saturation point (FSP) for immersion/dip treatment using a hot- and- cold bath open- tank process. Before oven-drying and subsequent treatment, individual test specimens were numbered, their green weights and volumes, and dry weights recorded for basic density, void volume, preservative uptake and retention determination. The poles were bundled and immersed (dipped) in a drum containing light tar-oil creosote. The tar-oil creosote with pine specimens was heated to boiling for 30 minutes and flames were extinguished with water to allow cooling. The cooling conditions, (dip time period for treatment) varied from 1, 5, 15 and 24 hours. Theoretically, a vacuum was created in wood during heating and when cooled, tar-oil was drawn into the wood’s anatomical structures. The experiment results indicated that tar-oil uptake and retention increased with dip time until available void volume was filled and no further uptake occurred. In this case, the preservative uptake and retention were proportional with square-root of dip time. The technique was simple with basic materials required for hot and cold bath treatment. This treatment technique is more appropriate for application at rural community level for treatment of utility posts/poles.
Keywords: wood preservation, hot and cold bath open tank process, tar-oil creosote, Pinus, Hoop Pine, preservative uptake/retention, immersion/dip time, natural durability