laminating deck beams

when cutting stock (VG DOUG FIR) for epoxy-lam deck beams, is the best practice, from a strength perspective, to run the saw cuts through the planer before glue-up or leave the relatively rough sawn surface for more tooth? the beams wont be visible in the end so i dont care about being able to see the glue lines, just trying to build the strongest way i can.

TIA

 

its stronger if you dont plane

 

It depends on what sort of sawcut you make and the type of glue and wood you're using. Titebond, resorcinal - the smoother the better. Epoxy is gap filling so it doesn't matter. Open wood pores are best, sawing and planing leaves them open compared to sanding which closes or clogs them.

 

Use a good quality sharp finish blade (10" 60-80 TOOTH) without planing and you'll save epoxy and get a good bond.

 

Yep, it depends on the adhesive. If epoxy, you can use a hatchet to make your strips. Most other adhesives will want clean cut tubules in the wood fibers and well fitted faying surfaces. If the surfaces are sanded, drag a sharp scraper over them, before gluing.

 

The arch-tops of this fence were laminated from 3 layers of knotty pine from local lumber store. Surfaces were used as supplied - very smooth. PVA outdoor glue used (not Titebond). None of the six arches show any signs of delaminating yet although it's still early days, nonetheless it suggests a good PVA adhesive should be fine for a highly-stressed joint subjected to frequent moisture.

Caveat: I read someplace that Titebond III loses 80% strength at 150 deg (C) so it may not be the best choice for a poorly ventilated dark-color structure in tropical areas. The other Titebond adhesives do better on the same test.