Glue Durability in Finger-Jointed Southern Pine

The structural laminating industry is rapidly converting from simple scarf joints to high strength finger joints for end jointing lumber. For those structural laminates that receive outdoor exposure, it is extremely important that the end joints withstand this exposure. The tests here reported yield some valuable information on end joint durability. Four glues were used: 1) a room temperature setting phenol-resorcinol formaldehyde, 2) a melamine formaldehyde, 3) a blend of 5 parts melamine formaldehyde to 3 parts urea formaldehyde, and 4) a urea formaldehyde strongly fortified with crystalline resorcinol plus paraformaldehyde. All specimens were cut from kiln-dried southern pine. Two triangular frames were formed with a 60? finger-jointed corner joint at each corner. The specimens were installed on a flat roof at Auburn, Alabama, where they were exposed to outdoor weathering for 9 years. Neither melamine formaldehyde nor a 5 to 3 blend with urea formaldehyde proved durable in southern pine end joints when exposed to outdoor weathering for 9 years at Auburn, Alabama. Phenol-resorcinol glue, and a urea formaldehyde strongly fortified with crystalline resorcinol, proved durable to such exposure for 9 years. While still structurally sound, 60? corner joints glued with phenol-resorcinol glue showed somewhat more glue failure after 9 years than did the four durable end joints. If this difference should prove consistent it would suggest that fingered corner joints with a thin scarfed region at the surface might be used as a demanding durability test for glues.

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