Heartwood of Siberian larch (Larix gmelini) and spruce (Picea jezoensis) was pressure treated with chromated copper arsenate (CCA) Type B using a full cell process. Larch heartwood was somewhat difficult to treat than the spruce, although both species did not meet a minimum requirements of penetration and retention specified by the American Wood Preservers' Association (AWPA) for difficult to treat wood species in ground contact. To improve the preservative treatability of refractory larch and spruce, end matched heartwood lumber had been incised using either a conventional or a double density incising pattern, and then pressure treated with CCA Type B. The use of double density incising is necessary for spruce heartwood in order to acheive adequate treatment with CCA; however, the increase in incision densities and/or the use of high treating pressure may be required for adequate treatment of larch heartwood.

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