Relationship of Oil Carriers to Utility of Pentachlorophenol as a Wood Preservative

Pentachlorophenol (penta) wood preserving formulations vary in composition between two extremes. The one extreme is a 5 percent solution of penta in a low-volatile residual oil. This formulation provides the best resistance against blooming, the best protection against deep checking of the wood in dry climates, and represents the lowest cost formulation. It is not suitable for components to be painted and has to be applied by pressure treatment. The other extreme is a 5 percent solution of penta in a formulation which is primarily mineral spirits. Since penta is not adequately soluble in mineral spirits, other components have to be added to obtain a composition which will retain 5 percent penta at the working temperature, and in which the blooming tendency is controlled. They may be further modified by the addition of waxes which act as water repellents. To minimize shipping costs, penta is frequently purchased as a concentrate containing 25 or 50 percent penta, which can be diluted at the point of use. The author points out that many of these concentrates do not contain solubilizing or anti-blooming agents, and hence simply diluting them with mineral spirits alone may not provide a satisfactory treating formulation. The commercial standard for the concentrate is CS 194-53.

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