Oscillating Pressure Treatment of 10 U. S. Woods

Ten U.S. species–Carya tomentosa Nutt., Quercus alba, Liquidambar styraciflua L., Pinus contorta Dougl., Picea engelmannii Parry, Larix occidentalis Nutt., Pseudotsuga menziesii var. glauca (Beissn.) Franco, Pseudotsuga menziesii (Mirb.) Franco, Tsuga heterophylla (Raf.) Sarg., and southern pine possibly Pinus echinata Mill.–were treated with copperized chromated zinc arsenate, Boliden salt S-25, by the oscillating pressure (OPM) process, and by the full-cell process. Thirty round posts 5 feet long by 5 to 7 inches in diameter and thirty posts 4 by 4-inch by 5-feet, mostly heartwood squares, were included for each of the ten species treated. Some round posts, 8-1/2 feet long and 5 to 6 inches in diameter, were also treated. These posts included another species, Taxodium distichum var. nutans (Ait.) Sweet. A 22-hour OPM schedule was used with cycles of alternating pressure and vacuum at intervals ranging from 1 to 6 minutes per cycle. A full-cell pressure period of 22 hours was selected to equal that of the OPM schedule. The study showed no significant improvement in heartwood penetration in the OPM process in 4 by 4-inch squares of mostly heartwood. Sapwood penetration in 5-foot long round green posts of six species was somewhat better after OPM treatment than after steam conditioning and full-cell treatment. In the longer 8-1/2 foot posts of southern pine and Liquidambar styraciflua L., the OPM treatment did not result in complete or uniform penetration of the thick sapwood. Results of the OPM process on the posts of Taxodium distichum var. nutans (Ait.) Sweet containing thick sapwood were also unsatisfactory. Treatment of round southern pine and Liquidambar styraciflua after vapor drying by both the OPM and full-cell processes was improved over the other methods.

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