IMPACT OF THREE ALTERNATIVE SURFACING PROCESSES ON WEATHERING PERFORMANCE OF AN EXTERIOR WATER BASED COATING
Oblique cutting, face milling, and helical planing were used to surface black spruce wood prior to the application of an exterior acrylic water based coating. Surface characteristics were assessed using an environment scanning electron microscope and coating performance was evaluated through pull off measurements before and after a 3 year natural weathering exposure. Microscopically, oblique cut surfaces were smooth with plateau like areas, had a low level of fibrillation and few open lumens. Face milled surfaces were characterized by a high level of fibrillation and numerous open lumens that favor coating spreading and penetration. Helical planed specimens had an intermediate level of fibrillation and number of open lumens. After coating application, oblique cut and helical planed surfaces presented similar overall visual quality, whereas face milled samples had an irregular appearance that degraded their quality. As a result, the latter were subjected to erosion during weathering exposure which further degraded their overall quality as well as pull off strength. More specifically, face milled samples had a significant inferior pull off strength both before and after weathering. Oblique cut specimens yielded higher initial pull off strength but were associated with higher adhesion loss. According to the results, helical planing reduces adhesion loss of the coating studied over a 3 year exposure to yield a superior pull off strength after weathering. Therefore, surfaces having a certain level of fibrillation still firmly attached to the surface and open lumens are desirable to increase mechanical anchorage of coating on black spruce wood surfaces.