An aging electricity distribution system and reduced availability of naturally durable tropical hardwoods in Australia will
combine in the next decade to produce a major shortage of poles. One approach to mitigating this shortage is to utilize lower
durability species and improve the penetration of preservatives into the refractory heartwood by introducing additional pretreatment
processes. A potential method for improving preservative penetration in the critical ground-line zone is throughboring.
This process, in which holes are drilled through the pole perpendicular to the grain in the ground-line zone, is widely
used in the western United States for treatment of Douglas-fir and may be suitable for many Australian wood species. The
potential for improving heartwood penetration in eucalypts with alkaline-copper-quaternary (ACQ) compound was assessed
on heartwood specimens from four species (Eucalyptus cloeziana F.Muell., E. grandis W.Hill ex Maiden, E. obliqua L’Her.
and E. pellita F.Muell.) and Lophostemon confertus (R.Br.) Peter G.Wilson & J.T.Waterh). Longitudinal ACQ penetration
was extremely shallow in L. confertus and only slightly better in E. cloeziana. Longitudinal penetration was good in both
E. obliqua and E. pellita, although there was some variation in treatment results with length of pressure period. The results
suggest that through-boring might be a reasonable approach for achieving heartwood penetration in some Eucalyptus species,
although further studies are required to assess additional treatment schedules and to determine the effects of the process on
flexural properties of the poles