Erosion Rates of Wood During Natural Weathering. Part III. Effect of Exposure Angle on Erosion Rate

This is the third in a series of reports on the erosion rates of wood exposed outdoors near Madison, Wisconsin. The specimens were exposed at an orientation of 90° or 45° facing south or horizontally (0°) for 10 years. Erosion was measured annually for the first 8 years and after 10 years. The erosion rates of earlywood (springwood) and latewood (summerwood) were determined for smooth-planed vertical-grained and flat-grained lumber (radial and tangential surfaces, respectively). Wood species included Douglas-fir, loblolly pine, southern pine, western redcedar, northern red oak, and yellow-poplar. Large differences were observed in earlywood and latewood erosion rates during weathering. For most species, the erosion rate increased as the angle of exposure decreased from 90° to 0°. A notable exception to this was observed for western redcedar, which had the fastest erosion at the 45° exposure. For some species, particularly western redcedar and southern pine (earlywood), erosion rates differed for tangential and radial surfaces. Little difference was observed between erosion rates of tangential and radial surfaces for the other wood species