Effectiveness of Groundline Treatments of Creosoted Pine Poles Under Tropical Exposure

Three proprietary groundline wood preservative formulations were applied to, weathered southern yellow pine pole stubs which had been treated with creosote. Fluoride-creosote, fluoride-arsenic, and pentachlorophenol gel compounds were studied to evaluate supplementary treatments of utility poles in a high rainfall, high decay-hazard tropical environment. The amount and distribution of sodium fluoride or pentachlorophenol after 1, 3, and 5-years was determined, and developing decay patterns in treated and untreated control stubs were also described. Based on soil-block threshold determination of 0.15 to 0.25 pound per cubic foot for sodium fluoride, all zones in an outer 3 inches treated with a fluoride-arsenic injection and exposed for 5 years were deficient. Pole stubs treated with a surface application of fluoride-creosote had above-threshold retention only in an outer 1/2-inch zone. Similarly, pentachlorophenol applied in a gel formulation had above threshold (0.10 to 0.20 pcf.) retention only in the outer 1/2-inch zone. After 8 years of storage and 5 years of ground contact, creosoted southern yellow pine control poles initially pressure treated to 14 pcf (gage) had oil residues of only 4 to 5 pcf (assay) in an outer 3-inch zone. These control stubs were severely attacked by decay fungi. The three proprietary groundline treatment formulations were highly effective in preventing decay.

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