Choosing The Right Adhesive

You'll find a woodworker in a sticky situation if his glue won't stick. How do you choose the all-around best adhesive for the job at hand? Here's some advice on what glues can and can't do.

Many woodworkers don't spend much time thinking about adhesives until they don't work. But learning a little about different types of adhesives makes good sense for any wood hobbyist interested in making sure that things go right.

Animal glues. Once widely used by woodworkers, these traditional adhesives have been replaced mostly by newer products. Hide glues must be heated in a glue pot before application. Reheating a project held together with hide glue allows you to readjust or remove parts. This also means that hide glues don't resist heat. And they have poor moisture resistance. Hide glues dry and cure slowly, meaning that they require a long clamping time. Casein glues are made from milk protein and come in powder form that must be mixed with water. They exhibit good strength, moderate water resistance, and no toxicity. Work with casein glue at any temperature above freezing.

Resin glues. These widely used woodworking glues made with polyvinyls or aliphatic resins come in white, yellow, and brown varieties. Because they're premixed, you apply them directly to the wood from their squeeze-type containers. Strong and somewhat fast-drying (about 3 hours clamp time), new formulas also offer extended water resistance. The white variety dries more slowly; the yellow and brown resist heat and moisture better. You can use resin glues in a wide range of temperatures.

Epoxies and thermosetting glues. Urea-formaldehyde, resorcinal-formaldehyde, and epoxy provide strong, permanent, highly water-resistant joints. They are, however, expensive and require mixing. And once mixed, a hardening chemical reaction begins, meaning that you have to work quickly before the mixture sets up, especially in warm temperatures. Although ffective for outdoor projects, adhesives in this category can irritate your skin and eyes.

Specialty bonding agents. Woodworkers use contact cement to bond plastic laminate or veneer to wood surfaces. It's applied to both surfaces and bonds immediately. Adjustments cannot be easily made, and the work area must be well ventilated. Cyanoacrylic glues are the so-called "super glues." They display exceptional strength and quick bonding with nonporous materials. New polyurethane glues perform like epoxies, but with no mixing and fumes. They expand as they cure, filling any gaps in joints. They're also waterproof.

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