Woodworker's Journal 2011-35-Winter, страница 44
Polyurethane: Oil-based Or Waterborne Our expert sets the record straight regarding p 0 l y u r e t h a n e ' s two distinct pedigrees. Like many other finishes, polyurethane is named for its primary resin, though some cans labeled "polyurethane" also contain other resins. Resin is what remains behind to form a film once the solvent has evaporated. The resin defines the nature of the coating. In general, polyurethane or urethane resins (the terms may be used interchangeably) provide finishes with good durability, including resistance to heat, abrasion, chemicals, stains and solvents. Polyurethane is tough enough for kitchen tables and cabinets, bathroom vanities, walls, doors, floors, all types of furniture and virtually any woodworking project. Woodworkers mainly use either oil-based or waterborne polyurethanes. Both have good qualities, but they are very different in many ways, giving rise to a hotly debated disagreement over which is superior. Oil-based Versus Waterborne The primary differences between the two relate to how they are made. Oil-based, whose proper name is "oil-modified urethane," is produced by reacting common finishing oils, like linseed oil, with a chemical that causes the oil to form larger molecules. A good rule of thumb is that larger molecules mean more durable finishes. The result is something that looks and acts like oil-based varnish, but is tougher. Polyurethane gel is simply a thicker version of the same thing. Waterborne polyurethane is an emulsion of resins in water and solvent. It dries fast and behaves more like lacquer than varnish. As a result, it benefits from a different application technique than oil-based, but there are also differences in durability, odor, flamma-bility, safety and even appearance. Let's compare the two in each major performance category. Durability Oil-based polyurethane wins this one hands down. It has better heat, abrasion, chemical and solvent resistance than its water-based cousin, and for a very good reason. Most water-based polyurethanes are actually a mix Oil-based and waterborne polyurethanes differ in durability, odor, flammability, safety and appearance — which is why there's a debate over which one is superior. 44 polyurethane: oll-based or waterborne |
