Prevention of Sapwood Discoloration in Hardwood Lumber

By EXECUTIVE SUMMARY Hardwood lumber drying in the South is subject to hot and humid weather that promotes enzymatic stain in sapwood. Research has long studied the problem and certain remedies have been proposed. Chemical dipping is the most commonly used method of preventing enzymatic stain. However, its application is only topical and does not prevent stain. A private operator, Danny Elder of Jasper, Texas, developed, through trial and error, a pre-drying treatment method called the Elder Process. The claimed benefits of the Elder Process include prevention of enzymatic stain; darkening sapwood color which more closely match that of heartwood and increases color consistency of lumber; reduce drying degrade; and reduction in air drying time. At the request of the local hardwood industry, the Texas Forest Service conducted a study to verify these claims. 13.3 thousand board feet of freshly sawn southern red oak boards were divided into four different treatment groups: a) Chemically dipped, not Elder Process treated (DNP); b) Chemically dipped, Elder Process treated (DP); c) Not chemically dipped, Elder Process treated (NDP); and d) Not chemically dipped, not Elder Process treated (control group, NDNP). The emphasis was on comparing the Elder Process to chemical dipping. The other groups were created to quantify any interaction between the groups. To quantify the change of color caused by the Elder Process, a Minolta CR-13 Color Reader was used to record the color difference between sample boards from these four treatment groups. To study the effect of the Elder Process on drying defects and drying degrade, all lumber was surfaced on both sides and then a National Hardwood Lumber Association inspector graded the kiln-dried lumber. Each board was graded with and without drying defects. Drying defects such as check and split, sap stain, sticker mark, and mineral stain were also recorded on both sides of the boards. To verify the effect of the Elder Process on air drying rate, air drying rates from two groups of boards (DP and DNP) were measured and compared. The color readings using the CIELAB color space for the pre-drying treatments clearly showed that the Elder Processed lumber had a brighter color with an orangey tint in the sapwood. This was closer to the color of the heartwood and showed improved color consistency between the sapwood and heartwood. The ∆E2000 color values between treatment groups showed that the Elder Process had a significant effect on sapwood …