How to pick the right bond for the job
With glue, the moment you step outdoors, all the rules change. What normally works just fine inside doesn’t stand a chance against moisture, freezing temperatures, and UV rays outside.
The most useful and widely available outdoor adhesives for small wood repairs and projects such as birdfeeders, storage boxes, and outdoor furniture are weatherproof carpenter’s glue, two-part epoxy, and polyurethane glue.
For wood joints on, say, a Muskoka chair or a birdhouse, weatherproof carpenter’s glue is inexpensive, non-toxic, easy to use, and easy to find. Look for words like “weatherproof” or “waterproof” on the label. The first generation of these glues carried the American National Standards Institute (ANSI) Type II water-resistance rating. Today’s leading formulations meet the more stringent ANSI Type I standard. Don’t be fooled by glues that only claim to be “water-resistant.” If a carpenter’s glue doesn’t say Type I or Type II, don’t use it outdoors.
Two-part epoxy has been around for years; it’s a strong glue that’s an ideal choice for porous and non-porous items. The most useful type for simple projects is five-minute epoxy because of its fast cure time. Measure and mix carefully, according to the package directions, for best strength. Five-minute epoxy is more expensive and viscous than the other two options so it only makes sense for small applications. Polyurethane glue looks like thick maple syrup (below). It’s also good for gluing porous and non-porous materials, though there is a catch:
Polyurethane glue needs a bit of moisture to trigger the curing process, and it expands as it cures. That’s why it’s best to dampen wood slightly before applying it, and to clamp joints. Excess polyurethane foams up as it cures and sands easily and cleanly when hard. Any remaining glue soaks up a finish better than the others, making it a wise choice for projects that you’re planning to stain a dark colour.
This article was originally published on May 20, 2006