A series of thermal diffusion treatments were carried out on unseasoned white spruce (Picea glauca (Moench) Voss) lumber and air dry aspen poplar (Populus tremuloides Michx.) timbers using an ammoniacal copper arsenate wood preservative. Under the specific conditions described, certain charges of lumber met the present Canadian Standards Association Wood Preservation Committee's requirements for wood in ground contact, having 10 mm penetration and 6.4 kg/m³ loading. The average preservative penetration in the heartwood of white spruce lumber ranged from 6.3 mm for charges of nonincised lumber to 13.9 mm for incised lumber. Preservative retention in the treated area was above 6.4 kg/m³ in four of the five charges of spruce lumber treated by this method. Aspen poplar timbers treated by thermal diffusion averaged 16.4 kg/m³ oxide retention. Post-treatment procedures such as close piling the lumber resulted in material with cleaner surfaces and more even penetration of preservative components.

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