Popular Woodworking 2009-10 № 178, страница 39
comes to bending wood or veneering? Would it be the best choice for gluing together green wood for bowl blanks or exotic woods for a cutting board or for outdoor furniture? Would you use yellow glue for gluing down a laminate countertop or a plastic cover over a fixture? Is yellow glue the best glue for inlay work which might involve wood, stone, shell, metal or leather? Is it the best choice for restoration, conservation or repairing a chair? Or what about the j oinery on fine furniture? Would it be the best choice for cabinets that will be subjected to high heat or moist environments? Don't get me wrong, yellow glue is a great product, but for many woodworking situations there is a better choice. Choosing the right glue can be a tough decision, especially with so many choices. Work-ability, bond-ability and price are key considerations. The following is an explanation of the seven families of glue used in woodworking. Hide Glue Hide glue comes from animals and is one of the oldest known glues. It's sold by gram strength, a complex test of physical characteristics and rigidity under specific conditions. There are grades of hide glue ranging from 85- to 512-gram strength. Woodworkers typically use hide glue at a gram strength between 164 (longer assembly time) to 251 (fast assembly time). Flake or pearl hide glue must be mixed with water and heated in a double boiler or glue pot to about 140°. The goal is to make a liquid of about the viscosity of white or yellow glue. As the water in the glue pot evaporates you need to add in more. In the old days you could tell where the cabinet shops were Rub the right way. Hide glue grabs as it cools, making it possible to make complex assemblies without the use of clamps. by smell; hide glues can have a strong odor if not prepared or used properly. Hide glue bonds as it cools to create a strong union that is reversible and resistant to creep in the joint. Because it grabs as it cools, the need for clamps can be eliminated, so complicated angles can easily be glued. It sands well, can take stain, has an indefinite shelf life in dry form, and what you don't use today can be recycled for future use. It's a resilient glue that is great for interior furniture and cabinets but it has no ability to withstand exposure to water. Hide glue is one of the glues of choice for period furniture makers, conservators, musical instrument makers and fine furniture makers. With practice it is a great glue for veneering. Hide glue is available in traditional form and in a ready-to-use liquid. Liquid hide glue has anti-gelling agents to prevent it from getting hard in the bottle and it cures through moisture loss rather than cooling so it has a longer open time. Liquid hide glues have a shelf life of about a year. PVA and Aliphatic Resins White (polyvinyl acetate) and yellow (aliphatic resin) glues are in the thermoplastic family and are made from synthetic compounds. Both are ready to use from the bottle, water-based, have low to no odor and are non-flammable. White and yellow glues are temperature sensitive, have a high degree of strength and are used for interior work. They're best suited for well-seasoned wood and have about the same bond strength. They cure in about 24 hours in normal conditions. Neither is water resistant; chemically they have similar characteristics. Both shrink while curing as they lose water. Neither is hard enough for structural bonds. There are cross-linking polyvinyl acetates (PVAs) available that are rated as weatherproof (Type II) or waterproof (Type III). White glues were introduced in the late 1930s and are one of the handiest glues available. They dry clear (not transparent), have great strength, provide some gap filling properties and cure at room temperature. White glue has a longer working time than yellow glue. It is also a little thinner and has a little less initial tack than yellow glue. Some furniture makers prefer white glue for these reasons. Some downsides are that it is not stainable and it can allow the wood to creep when movement takes place. White glue also tends to clog sandpaper. Good old glues. Polyvinyl acetates (White) and aliphatic resins (Yellow) are standard all around woodworking glues. Yellow glues hit the scene in the early 1960s. They are white glues with additives (resins) that give them different characteristics. Yellow glues are thicker, tack faster and can be applied in cooler temperatures than white glues. They have a shorter work time and a faster clamp time and offer slightly better resistance to heat, but they are still temperature sensitive. Yellow glues are less likely to allow joints to creep. They sand much better than white glues (but still can clog sandpaper). Yellow glues have a better ability to bond to woods with slightly higher moisture contents. Some downsides of yellow glues are that they dry with a yellow line that is noticeable in light-colored woods. They also have a shorter working time which can cause some urgency when applying. Yellow glues are great for interior furniture and cabinets, especially in production work. "Cross-linking" and "Specific Purpose" PVAs are formulated to be water resistant or waterproof, and some can be cured by radio frequency. There are special glues with non-drip formulas, extending agents which allow for a greater working time, gap filling, non-bleeding glues for veneering and even a version that shows under UV light. They even make PVA glues with glitter in them. Urea Formaldehyde Urea formaldehydes (also referred to as plastic resins) are water, heat and creep resistant. They are great glues for most indoor furniture and cabinets. They are in the family 52 ■ Popular Woodworking October 2009 |
