Treatability of Western Hemlock Lumber from Coastal and Interior British Columbia Regions with Water Borne Preservatives

Kiln-dried 2 by 4-in. specimens of western hemlock (Tsuga heterophylla (Raf.) Sarg.) from one interior and two coastal areas of growth were pressure treated with chromated copper arsenate (CCA) and ammoniacal copper arsenate (ACA) to determine whether area of growth affected the treating properties of the species. Preservative retentions and penetrations were more than twice as great in coastal-grown specimens as in interior-grown specimens. In all specimens, sapwood accepted treatment better than did heartwood. CCA retentions were about 7 percent higher than ACA retentions in specimens from the coastal sources, although ACA generally penetrated more deeply into the boards. An air-permeability device was moderately successful in segregating easy-to-treat specimens from refractory ones.

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