Southern pine sapwood is non-durable, and preservative treatment is necessary to protect it against biological degradation. According to AS 1604.1 2021, timber products must have their sapwood fully treated with preservatives for various applications and hazard classes. However, there is a growing industry concern over the refractory sections of sapwood, which are untreated pockets of wood that do not absorb preservatives effectively after vacuum pressure treatment. This study investigated some wood anatomical differences between treated and refractory southern pine sapwood subjected to light organic solvent preservative (LOSP) treatment. The study utilised light microscopy, safranin solution uptake, and microcomputer tomography (µCT) to identify any differences between the two types of sapwood. Light microscopy results showed wood rays and horizontal resin canals were sapwood's main lateral liquid movement path. Furthermore, in refractory sapwood, the movement of liquid from rays to the tracheid was interrupted. µCT imaging results showed interrupted pathways within refractory samples. Safranin uptake comparison between treated and refractory sapwood showed that treated sapwood had higher liquid uptake capacity. The assessment using µCT images showed that the treated sections of sapwood had a higher proportion of voids in resin canal areas and a greater percentage of uninterrupted voids within the sample volumes than the untreated sections. Comparison between refractory sections with and without resin canals showed that the presence of resin canals increased the void connectivity in refractory sections.

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