End Gluing of Green Lumber

Impression finger jointing, a hot-die process of joint formation, makes end gluing of green lumber possible. The action of the hot die on green wood leaves the finger surfaces in a suitable condition for gluing. Improved lumber recovery could result from end gluing of green lumber in sawmills. Green lumber of Douglas-fir, western larch, grand fir, and western redcedar were impression finger jointed at moisture contents ranging from 28 to 220 percent. The adhesives used were resorcinol, phenol-resorcinol, melamine-urea, and casein. When joints were tested 3 – 5 days after bonding but before the lumber dried, average joint strength in Douglas-fir and larch ranged from approximately 3,000 to 6,000 psi in modulus of rupture. After air-drying to equilibrium, joint averages ranged from 9,000 to 11,000 psi. Gluing and mating joints while they were hot from the die was better than allowing them to cool before gluing. Supplemental heating of the green joints after gluing also improved joint strength. Thee bending and tensile strength of impression finger joints formed in green lumber and then air-dried was comparable with joints formed in dry lumber. Also, joint strength was approximately the same after air-drying as after kiln-drying. Impression finger joints were evaluated for glue-bond durability in cyclic humidity, continuous wet, and cyclic wet-dry conditions. All tests showed that impression finger joints are structurally sound in extreme or in wet-use conditions.

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