A New Method of Applying Pentachlorophenol to Wood in Place

The procedure for applying a thickened emulsion form of a penta-petroleum solution is described in U.S. Patent No. 2,708,640 and is known as the Davis Patent. The trade name for the emulsion is Woodtreat. This oil-in-water emulsion is applied as a semi-stable, highly viscous, self-sustaining product that forms a heavy coating over the wood to be treated. Woodtreat contains 87 percent by weight of an aromatic petroleum solvent containing 10 percent pentachlorophenol. The remaining 13 percent is stabilizers and water. The effectiveness of the Woodtreat formula was tested by a comprehensive series of laboratory and field tests. The field tests involved matched untreated western redcedar pole stubs 5 feet to 6 feet in length and unmatched creosoted southern pine stubs. The pole stubs were placed in the ground, backfilled, and allowed to reach an approximate equilibrium with the soil moisture. The emulsion was applied with a trowel to a thickness of 1/4 to 1/2 inch. The Woodtreat was compared with samples treated with a standard 5 percent penta-petroleum solution. All pole stubs were bored after remaining in the ground 1 month after treatment. One set of borings was obtained at the ground line, one set 10 to 12 inches above grade, and one set 10 to 12 inches below the ground line. The results for the redcedar pole stubs at a depth of 1/2 inch from the surface were 0.753, 0.920, and 0.598 lb. of penta per cubic foot of wood 1) where backfilling was delayed, 2) there was immediate backfilling, and 3) stubs were wrapped, respectively. By comparison, the penta retention results obtained by the Woodtreat application were 4 to 7 times as great as for the standard penta-petroleum solution at the 1/2 inch depth and 4 to 5 times as great at the 1 inch depth. The same comparisons for the southern pine were 6 times as great at the 1/2 inch depth and 6 to 11 times as great at the 1 inch depth. Laboratory tests were made involving the use of matched 2 inch by 8 inch by 2 foot flat-grain, clear southern yellow pine, Douglas-fir, and red oak. The test sections were oriented to measure end, tangential, and radial penetration. The different thickness levels of Woodtreat application were 1/16, 1/8, 1/4, and 1/2 inch. These were compared with the standard 5 percent penta-petroleum solution which was applied with a brush in 10 and 20 coat levels. A 3-minute dip treatment was also included. The significant results were as follows: 1) Retention increased by species as follows: pine, oak, and fir; and 2) a 1/2-inch-thick end grain application of Woodtreat was 5 to 10 times as effective as 20 brush coats of the standard solution.

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