Influence of Grain Direction on Penetration, Retention, and Leaching of CCA(C) in Sapwood and Heartwood of Kenyan-Grown Cupressus lusitanica and Pinus patula
The influence of grain orientation on penetration, retention, and leaching of CCA (C) was tested on small samples of sapwood and heartwood of Cupressus lusitanica and Pinus patula. Samples measuring 50mm x 50mm, and 200mm in the longitudinal axis were sealed to expose only transverse, or radial, or tangential faces, pressure treated with 6% CCA (C), and penetration, retention and leaching of the preservative measured. Generally, the normal trend of Transverse > Radial > Tangential was observed for penetration, retention and leaching in sapwood and heartwood of both species, and in the three grain directions. Penetration in sapwood samples of both C. lusitanica and P. patula were higher than in heartwood samples, being significantly higher in the transverse grain direction. Both retention and leaching reflected on the depth of penetration of the preservative in samples. Retention was generally lower in the three grain orientations in both sapwood and heartwood of C. lusitanica samples. However, it was noted that retention in the radial and tangential grain directions in sapwood and heartwood of both species were not significantly different. Leaching followed the same patterns as for penetration and retention, that is lower in both sapwood and heartwood samples of C. lusitanica, being high in the transverse grain direction in sapwood and heartwood of both species, low in the radial, and lowest in the tangential grain directions. However, leaching in the radial and tangential grain orientations in heartwood samples of both species were fairly similar. Generally, P. patula samples achieved higher penetration and retention, but amounts of the preservative leached out were also higher. The results of the work clearly shows that sapwood, heartwood, and grain orientation all influence penetration, retention, and leaching of CCA (C) in two species of softwoods tested, and that is likely to be the case with most softwoods. The implications on treatment schedules have to be considered.