Adhesive bonding of wood treated with ACQ and copper azole preservatives

Treated wood has generally been more difficult to bond than untreated wood for a variety of reasons. Alkaline copper quat (ACQ) and copper azole (CA-B), the most prominent substitutes for chromated copper arsenate (CCA), are difficult to bond consistently. Using a phenol-resorcinol-formaldehyde (PRF) adhesive formulated for bonding to CCA-treated wood, we examined the bonding of southern yellow pine treated with CCA, ACQ, or CA-B. In durability tests, bonds were not as durable in the ACQ- or CA-B-treated southern yellow pine as in the CCA-treated or untreated pine as measured by delamination. Using differential scanning calorimetry (DSC), we determined that the adhesive tends to react more quickly with ACQ- or CA-B-treated southern yellow pine than with untreated or CCA-treated southern yellow pine. A hydroxymethylated resorcinol primer (HMR) did not penetrate as well into ACQ- or CA-B-treated southern yellow pine as into untreated wood, suggesting that PRF penetration is not as effective in treated wood. However, the HMR primer was able to reduce the extent of bond delamination of treated southern yellow pine bonded with PRF.