Surface Checking and Drying Behavior of Pinus Radiata Sapwood Boards Treated with CCA Preservative

Surface checking in 2-inch backsawn sapwood boards of Pinus radiata D. Don was analysed in relation to drying conditions (high temperature – 240?F dry bulb and l6?F wet bulb; low temperature – 180?F dry bulb and 160?F wet bulb) and full-cell pressure treatment with 1.25 percent copperchrome-arsenic solution or water. Drying times to about 14 percent moisture content for untreated, water-treated and CCA-treated matched boards dried at high temperature were 35, 52, and 63 hours respectively and at low temperature were 160, 161, and 246 hours respectively. Moisture content gradients across the drying boards were very much steeper in CCA treated boards than in untreated ones at low temperature drying conditions but only slightly steeper in CCA boards than in untreated ones at high temperature conditions. The gradients were considerably steeper in untreated boards dried in high temperature than in low temperature conditions. Unsteady state desorption integral diffusion coefficients were determined between 18 and 12 percent moisture content with 1-inch boards which were untreated, CCA- or water treated and had been dried at both temperatures to 20 percent moisture content. There was no apparent effect of temperature, but the CCA boards gave consistently lower values than did the water treated or untreated. Internal checking was observed to be severe in high temperature dried boards, treated or untreated, but totally absent in low temperature dried ones. Surface checking during initial drying was greater in high temperature conditions. During redrying after treatment it increased in all boards, with the greatest increase in those which were CCA treated and low temperature redried, and less increase in those which were water treated and dried at low temperature, and the least in high temperature re-dried boards after either treatment. Surface checks were found to originate in vertical resin canals which ran along or close to the surface of the drying faces in backsawn boards. In almost all cases the majority of checking was on the face nearest to the bark.

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