Popular Woodworking 2007-08 № 163, страница 69
Proof that less strength and water resistance compared to most modern adhesives aren't serious problems is the survival of so much furniture made before the 1950s. (Actually, I think the bad reputation began in the 1950s when manufacturers claimed superior strength and water resistance for their white and yellow glues to get craftsmen to switch. These non-issue claims are still used today by suppliers of even stronger and more water-resistant adhesives.) Disadvantages and Advantages Nevertheless, hide glue still has a number of disadvantages compared to modern adhe-sives. Hot hide glue has to be prepared in advance and applied hot. It sets up too fast for relaxed assembly and has a relatively short pot life (several weeks at room temperature) before it begins rotting and losing strength. So there is usually a lot of waste. In addition, and not least important, hot animal hide glue has an aroma many find unpleasant. But the glue has two unique advantages over all other adhesives: reversibility and quick tack. Both are far more useful for repairing old furniture glued originally with hide glue than for making new furniture. I don't buy the argument that you should use hide glue on new furniture so it can be repaired more easily decades from now. It's rare that today's repairmen recognize the glue, so what are the chances tomorrow's will? So there's little likelihood they will take advantage of hide glue's easier repairability. The best argument for using hide glue is to stay true to the original when making reproductions. Glue-blockstrength. These glue blocks in the inside corner of a mid-19th-century Empire chest-of-drawers are still strong. Glue blocks were commonly used in corners to add strength. Keep it covered. A commercial glue pot maintains the temperature of the glue at an ideal 150°. To retard evaporation and the glue thickening, I keep the pot covered with a plastic lid. The lid has a cut out for brushes and a stirring stick. Reversibility Reversibility is the quality that makes redis-solving possible after the glue has dried. It allows you to reglue loose j oints without first having to remove the old glue (to create clean wood). Simply remove any loose or powdered glue, apply fresh hot hide glue, and reassemble. The moist heat of the new glue dissolves the old glue and the two combine to create a strong bond. Though it's fairly easy to remove white and yellow glues by soaking and scrubbing with hot water or vinegar, no freshly applied glue redissolves into these glues. Other adhesives, including polyurethane, epoxy, plastic-resin and cyanoacrylate, can't be broken down. They have to be scraped off which can't help but remove some of the wood, resulting in loose-fitting joints. Reversibility also makes cleaning hands and removing glue seep age from newly assembled joints a relatively quick and easy task. Simply rinse or wipe with hot water. And it makes separation of sound glue joints possible by injecting hot water, steam, vinegar or denatured alcohol (which crystallizes old hide glue). Initial Tack Unlike other adhesives, hot animal hide glue bonds in two steps. An initial tacking occurs when the glue cools from its application temperature of 140-150° Fahrenheit to about 95°F. The bond becomes complete when the water evaporates out of the glue. The initial tack allows you to glue two pieces ofwood together without clamps. Sim- Heating options. You don't need to invest in a glue pot. Any situation you can arrange that will keep the glue at about 140° to 150° will work well - in this case a jar of glue in a pan of water on an electric hot plate. Keep an eye on the temperature. ply apply the glue to both surfaces and rub the pieces together to work out the excess glue. As the glue cools, it gels and the pieces begin to stick. Position them correctly and let the glue dry to complete the bond. As long as the pieces are not forced apart while the glue is still in the gel state, the tack is strong enough to create a good bond. On the other hand, if you don't like the positioning of the pieces, you can separate them for some time before the bond becomes too strong. The glue blocks you see behind legs and on the inside corners of old case furniture were positioned with this rubbing technique, called a "rub joint." It's not uncommon to see glue blocks still sound after 200 years, especially if the grain of both parts runs parallel. You can use a rub joint to replace broken pieces on carvings, small pieces ofveneer, and other parts that would be difficult to clamp. You can also strengthen case furniture by regluing old glue blocks or by inserting new Finger test. Rub joints work well with hot hide glue because of the strong tack created when the glue cools to about 95°F. Use your fingers to check the strength of the glue as it ages and loses tack. The glue cleans off quickly in hot water. popularwoodworking.com ■ 83 |
