Cross-Grooved Stickers Reduce Marking on FRT Plywood

Stickers with grooves perpendicular to the edge and at an angle of 45 degrees to the edge were effective in reducing the incidence and severity of discoloration (sticker marks) in plywood treated with commercial fire-retardant chemicals. Douglas-fir plywood panels, separated by three 3/4-inch stickers, were dried in a small kiln or in an oven with similar time-temperature schedules. Charges of panels were weighted to estimated sticker loadings of 1, 4, and 7 pounds per square inch. Whether the stickers were wet or dry, treated or untreated, did not seem to influence severity of staining. Discoloration was more pronounced under cedar than under Douglas-fir stickers. Small specimens treated with a mixture of borax and boric acid and panels treated with fire retardant B showed conspicuous discoloration. When plywood treated with certain fire retardants is dried, low initial temperatures may be necessary to prevent crystals from forming on the surface.

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