Evaluating warp of 2 by 4s sawn from panels produced through green gluing dimension lumber from small ponderosa pine logs

Overstocked small-diameter softwood timber in western US forests has created a serious forest health and fire hazard, and the costs of removing this material are high. One way to lower costs is to reduce loss because of warp on lumber sawn from these small logs. Using a green-gluing process, standard 38 by 89-mm (nominal 2 by 4-in.) pieces (2 by 4s) ripped from pressed panels of edge-glued (edge-glued-and-rip [EGAR]) boards sawn from small ponderosa pine ( Pinus ponderosa ) logs were evaluated for warp reduction. Material was bonded at high moisture content (MC) to simulate lumber freshly sawn from water-saturated logs and examine potential MC effects on wood–wood bonding. We selected a liquid, one-component, fast-curing, cold-setting polyurethane for green gluing wood. Results showed statistically significant reduction in bow ( P < 0.001) and twist ( P < 0.001) and no statistical difference in crook ( P = 0.321) for EGAR boards compared with conventional 2 by 4s before planing. After planing and equilibrating, EGAR boards showed statistically significant increases in crook ( P < 0.001) and bow ( P < 0.001) but maintained a statistically significant reduction in twist ( P < 0.001). Lumber quality decreased after planing and equilibrating to 12 percent MC. Because of high MC in flitches during the green-gluing process, bondline failures sometimes occurred, distorting the final results. High amount of bondline failure after planing and equalizing indicates this process is unfeasible as tested. Greater MC control during green gluing may reduce warp to allow more effective utilization of these small logs.