Experimental trials at FRI, Rotorua showed that the steaming schedule normally used for steaming and venting is also suitable for steaming and vacuum seasoning. Applying vacuum of up to -84 kPa immediately after steaming did not increase the initial loss of wood moisture significantly in comparison to steam/venting. The main improvement to wood condition by using steam/vacuum appeared to be to distribution of moisture within, and possibly between, posts. Bethell treatment of Corsican pine posts one day after steam/vacuum was not of a satisfactory standard. However, the steam/vacuum/Bethell system may offer a worthwhile reduction in the holding period specified for the steam/vent/Bethell ('Q') system. A shortened and simplified Alternating Pressure Method (APM) process was used to treat Corsican pine posts one day after steam/vacuum. The standard of treatment obtained by using this system was evaluated at FRI and at a commercial treatment plant and showed potential to treat wood to low retention variability. As a result of these trials the New Zealand Timber Preservation Authority has approved a steam/vacuum/APM schedule for the treatment of radiata and Corsican pine rounds up to 250 mm large end diameter.

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