Popular Woodworking 2009-10 № 178, страница 40
of thermoset plastics that cure chemically and require mixing to harden. They spread easily and are impervious to most solvents once they cure. Resin glues tend to generate heat as they cure which can cause issues with some inlay materials. They have a long working time which causes the clamp time to be long as well, up to 12 hours. They are temperature sensitive during curing and must be applied at 72° Fahrenheit or more. After they cure, temperature is not an issue. They are not the best gap-filling glues and they have a darker color, although some manufactures sell additives that lighten the resin. Resin glues can also be cured through a process called "high frequency gluing," which takes the normal cure time from 24 hours to just a few minutes. Urea formaldehyde is one of the best choices for veneering, laminate bending, structural applications, and cabinets and furniture that could be exposed to excessive heat or higher humidity. Some of the downsides are that they have a short shelf life and can cause health problems. They require carbide cutters when cutting because the cured hardness is brutal on tools (as is cured squeeze-out on hands). Wear safety glasses and a dust mask when working, machining or sanding. Epoxy Epoxies are great waterproof glues. They are two-part glues that produce strong bonds on many different materials including some plastics, stone, metals, ceramics, plastic laminates and resinous woods such as teak or rosewood. Epoxy loses about 1 percent of its volume as it hardens so there is basically no shrinkage, which makes it a good gap-filling glue. It dries with a clear or slight yellow color, but non-yellowing and high-clarity epoxies are available. It's also possible to add dyes to turn it any color you wish. Epoxies can be rolled, brushed or troweled and they can penetrate wet surfaces well, but they have little or no initial tack, so clamping is important to keep parts from sliding. Clamp pressure should be light with epoxies to prevent total glue squeeze out. Epoxies sand easily and are solvent-resistant but they are not heat- or UV-resistant. Epoxies are a great choice for outdoor furniture, boatbuilding, working with exotic lumbers, inlaying just about anything and structural applications. They are shock resistant and thus perfect for gluing together items like wooden mallets. Polyurethane Polyurethane glues have been around for quite some time but didn't hit the American woodworking market until the early 1990s. Polyurethane glues have about the same cured strength as yellow glues and stick to just about anything. They foam during the curing process, and the foam that fills gaps is largely air, not solids. At first they were touted as waterproof but they are only water-resistant. Polyurethanes Flat forever. Plastic resins form an ideal bond for complex veneering (as in this table made by Markee Adams) and other tasks where creeping is an issue. Filled with foam. Polyurethane glues foam as they cure. This adds no strength to any gaps and can be a pain to remove. are heat-resistant and rigid so they are good at resisting creep along joint lines. They are activated by moisture so dry wood should be moistened first and they offer about a 45-minute working time. Because poly uret h ane glues h ave a tendency to sit on the surface of the wood instead of being absorbed into it as with water-based glues, they won't create a staining issue if cleaned off properly. However any polyurethane that remains on the surface will not accept stain. It's a good glue choice for outdoor furniture. Polyurethane glues are difficult to clean up while they are still liquid but once cured they can be sanded or chiseled off. They work well with exotic woods and do not have a tendency to become brittle with age like most glues. They have a short shelf life and are expensive. Wear gloves when you apply it and be prepared for some real challenges during cleanup around the joint because of the expanded foam created as the glue cures. Polyurethane glues will bond anything to anything and they excel at gluing woods with higher moisture contents. Cyanoacrylates or Super Glues Super glues were developed at Kodak Laboratories in 1942 but were shelved for several years until the 1960s when they were introduced through the TV show "I've Got a Secret." They were submitted to the FDA as a material to hold human tissue together for surgery. Today super glues have found their way into every imaginable application. Super glues cure to a solid that is similar to a sheet of acrylic. They can be activated by many ways depending on the formulation but the most common way is by reacting with the water in the wood. If you choose to use an activator or accelerator be aware that the bond will be slightly weaker and popularwoodworking.com ■ 53 |
