Replies

1. 
   woodrae | May 10, 2007 06:02am | #1

   Dennis—

   Polyurethane glues are fine for bent laminations, and they won’t creep since they’re not susceptible to moisture like white and yellow PVAs (polyvinyl acetates). But I don’t use ‘em.

   I dislike poly glues for laminations for a variety of reasons, but this doesn’t mean you can’t use them yourself very successfully if you follow a few precautions. The downsides for me, and what to watch for, are: They can be a bear to work with, as they stick to everything, stain fingers and hands, and you need a stronger solvent than water to clean them up; workpieces must be pre-wetted to increase the wood’s moisture level, which activates the glue; and you can have potentially disastrous results if you don’t pay attention to the fact that the glue expands as it cures, causing foaming and possibly pushing apart of your joints if everything isn’t clamped down tight. Did I mention the mess?

   My favorite glue for bent laminations is the resin/powder variety of urea formaldehydes, also called plastic resin glues. I use Unibond 800, one brand of this type of glue. It dries super hard, which reduces springback; it won’t creep; it has a long (20 min. or more) open time; it dries fast (in an hour, possibly three depending on how you mix it and if it’s cold; unlike the water/powder variety, which can take 12 hours or more clamping time); and it cleans up with water. The only downside, other than the price (which is comparable to poly glues) is the odor, which can be very harmful to your body. Use good ventilation if you’re using a bunch of this stuff.

   You can buy Unibond 800 from Vacu-Pressing Systems, or a similar resin/powder urea glue from Constantine’s.

   Good luck,

   Andy