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 expos ed outdoors near Madison, Wisconsin. The specimens were exposed at an orien tation of 90 degrees or 45 degrees facing south or horizontally (0 degrees) for 10 years. Erosion was measured annually for the first 8 years and afte r 10 years. The erosion rates of earlywood (springwood) and latewood (summe rwood) were determined for smooth-planed vertical-grained and hat-grained l umber (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 la tewood erosion rates during weathering. For most species, the erosion rate increased as the angle of exposure decreased from 90 degrees to 0 degrees. A notable exception to this was observed for western redcedar, which had th e fastest erosion at the 45 degrees exposure. For some species, particularl y western redcedar and southern pine (earlywood), erosion rates differed fo r tangential and radial surfaces. Little difference was observed between er osion rates of tangential and radial surfaces for the other wood species.