Performance of Eastern Hemlock Wharf Timbers

A pathological examination was made on 27 wood specimens which were obtained from a total of 369 inspected round piles and squared timbers,and which had been installed 7 years previously in a fresh water wharf near Mont-Laurier, Quebec. Timbers, consisting of braces, caps, decking, fascia, piles, wales, and wheelguards, had been treated by either one of two processes. The first was a full-cell pressure process employing a preservative containing fluor-chrome-arsenate-phenol Type B salts. This preservative, which was composed of sodium fluoride (34 percent), potassium dichromate (34 percent), sodium arsenate (25 percent), and dinitrophenol (7 percent), gave a retention of 0.5 pcf according to the American Wood Preservers’ and Canadian Standards Associations’ specifications in use at the time of treatment. The second process, non-pressure diffusion treatment, was conducted by brushing the wood with a concentrated form of the same salts at the building site. Pressure-treated round bearing-piles of red pine (Pinus resinosa Ait.), exposed to severe leaching because of fluctuating water levels, were in sound condition. Two square-sawn, pressure-treated eastern hemlock (Tsuga canadensis (L.) Carr.) caps on an inclined ramp were also subjected to considerable leaching and were obviously decayed. However, those caps above the water line and those which were submerged remained sound. Four other structural timbers of eastern hemlock, which had also been square-sawn, were decayed. Pressure-treated beech (Fagus grandifolia Ehrh.) and red oak (Quercus rubra L.) braces showed no evidence of decay. Red pine decking, fascia, fenders, and wales constructed from white spruce (Picea glauca (Moench) Voss), eastern hemlock and beech, which were all pressure treated, were in good condition. Diffusion treatment was satisfactory for white spruce wheelguards, but decay was found in an eastern hemlock curb block exposed to mild decay hazard.

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