Lumber warp is the primary cause for drying degrade. Over the past decade, Canadian producers have been paying increasing attention to the box-store market and that of engineered wood products such as wood I-joists and glued-laminated beams (glulam). One characteristic of these markets is that they require straight and stable lumber. The objective of this study was to determine the effect of sticker spacing on stickering costs and lumber quality.
To address this objective, we conducted tests in three stud mills. Stickers were added as required for the assessment of 48-, 32-, 24- and 16-inch spacings, i.e. 3, 4, 5 and 7 stickers respectively with 8-foot lumber. The bundles of test lumber were dried in a single load in all mills. After drying, the lumber was graded by a grading agency inspector. He determined the potential grade before drying and the actual grade after drying for each piece of lumber. The moisture content (MC) of the test lumber was also determined on a sample basis.
In Mill 1, we observed that drying degrade for the entire sample was reduced from 2.2 to 1.3% in the bundles spaced at 24 inches, which represented a gain of $3.21/Mbf. As for lumber meeting the requirements for the special grade, degrade was reduced from 71.3 to 49.5%, which is a gain of $10.41/Mbf.
In Mill 2, drying degrade decreased from 32.1 to 26.3% when sticker spacing was reduced from 48 to 32 inches, for an approximate gain of $1/Mbf. In this particular mill, a 16-inch spacing failed to improve performance over a 32-inch spacing.
As for Mill 3, reducing sticker spacing from 48 to 24 inches decreased drying degrade in the special grade lumber by half, leading to a $5.33/Mbf gain. Drying degrade decreased regularly from 48 to 32 inches and from 32 to 24 inches. Closer spacing benefited lumber quality at both the top and the bottom of the stacks.
Optimal spacing in a sawmill should be based on species and stickering costs. As costs vary widely from mill to mill, the report provides information to help users calculate additional stickering costs. We observed significant gains from reduced sticker spacing. Twenty-four-inch spacing should become standard practice in the manufacture of quality lumber. As a rule, closer spacing requires only limited investments, i.e., the acquisition of additional stickers and, occasionally, minor modifications to the stickering equipment.