The effectiveness and penetration in heartwood boards of an LOSP formulation containing TBTN was examined by determining decay resistance to the white-rot fungus Perenniporia tephropora. Boards, one metre long, of Eucalyptus regnans, Eucalyptus delegatensis, Eucalyptus obliqua and Eucalyptus sieberi were treated, along with boards of 'light' and 'dark' meranti. After treatment, blocks were cut from various positions along the boards, including one block from the end grain. All except the end grain blocks were coated with epoxy on their freshly cut end grain surfaces to ensure fungus attack occurred only through the lateral surfaces. Some of the blocks were left intact or unshaved, while others had 2 mm of surface wood (treated envelope) removed by shaving. Eucalyptus sieberi was the most preservative absorbent species examined, providing a mean retention of 51.2 kg/m³. Eucalyptus obliqua absorbed least preservative (15.7 kg/m³). Eucalyptus regnans, Eucalyptus delegatensis, light and dark meranti absorbed similar amounts of LOSP, giving mean retentions between 24.9-33.6 kg/m³. There was resin bleed from two of the meranti specimens after treatment, whereas no exudate or kino bleed was produced by the treated eucalypts. Perenniporia tephropora was unable to decay the untreated heartwood of both Eucalyptus sieberi, and Western red cedar (Thuja plicata), and produced minor decay in some Eucalyptus obliqua blocks. Untreated blocks of the other timbers were decayed. LOSP treatment improved the decay resistance of the end grain blocks from light meranti, dark meranti, Eucalyptus regnans and Eucalyptus delegatensis, however only light meranti gained significant protection after treatment in blocks cut from the remaining positions along the board.

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