The adhesion of an acrylic primer to weathered radiata pine surfaces

Radiata pine (P. radiata) heartwood and sapwood were cut to produce flat-grain blocks in which the upper tangential surface consisted of either earlywood or latewood. Blocks were subjected to 6 weeks of weathering during an Australian summer and coated with an acrylic primer; and the adhesion of the primer to the different weathered and unweathered wood surfaces was assessed using a tape test. Primer adhesion decreased on earlywood as a result of weathering, but increased on latewood. Scanning electron microscopy (SEM) observations of wood/primer interfaces after tape testing suggested that the increase in primer adhesion on weathered Jatewood was due to greater penetration of the primer into relatively undegraded subsurface tracheids. There was little difference in the adhesion of the primer to heartwood or sapwood, but, as expected for unweathered surfaces, primer adhesion was greater on earlywood than on latewood. The practical implications of these findings for the coating of exterior wood are discussed briefly.