Distribution and Effectiveness in Pinus Sp. of a Water-Repellant Additive for Water-Borne Wood Preservatives

A water-repellent additive developed for use with waterborne copper-chrome-arsenate (CCA) preservatives was impregnated into blocks of Baltic redwood (Pinus sylvestris) 1.6 by 1.0 by 0.6 inch by a vacuum/pressure technique. The additive contained a radioactive marker, n-octadecane-1-C14. The blocks were allowed to dry after treatment and sections 20 microns thick were cut and prepared for autoradiography. After 11 months storage the autoradiographs were developed. Optical microscopy showed that the radioactive water-repellent was distributed throughout the blocks and was concentrated in the summerwood rays, the tissues which are most susceptible to weathering degrade in untreated timber. Matched samples cut from a single length of Baltic redwood and a single length of southern yellow pine were vacuum/pressure treated with either a CCA preservative (‘Tanalith’ C) or a CCA preservative containing a water-repellent additive (‘Tanalith’ C Plus). After air-drying the samples were planed to different depths on the tangential sapwood surfaces. The Baltic redwood samples were artificially weathered on a cyclic weatherometer for 7 weeks and the southern yellow pine samples for 20 weeks. Visual examination of the weathered surfaces showed at the end of these periods that the water-repellent was effective to a depth of at least 1/2 inch in Baltic redwood and 5/16 inch in southern yellow pine. The distribution and depth of effectiveness in service of a formulation containing a relatively small amount of water repellent.

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