Treatability of SPF Framing Lumber with CCA and Borate Preservatives

There is increasing interest in preservative pressure-treatment of framing lumber to prevent attack by decay fungi and insects. However, the Spruce—Pine—Fir species group that is often used in framing construction can be difficult to penetrate with preservatives. We compared solution uptake and penetration of boron and copper from a borax—copper (BC) preservative to that of boron in a disodium octaborate tetrahydrate (DOT) treatment and copper in a chromated copper arsenate (CCA) treatment. For all wood species, average solution uptake was consistently greater with the DOT solution than with the BC or CCA solution. Average boron penetration with DOT was also greater than that for any BC solution. Immediately after treatment, boron penetration with DOT exceeded 10 mm in at least 80% of specimens, indicating that the treatment could meet American Wood Preservers' Association (AWPA, 2003) penetration standards. Following a 2-week diffusion period, boron in BC treatments also met or exceeded AWPA standards in most cases. Copper penetration was much lower than boron penetration and did not meet AWPA standards in any species. Collapse was noted in some specimens treated with heated BC and DOT solutions