Oil vs. Film, Choose Your Finish
When it's time to apply a knockout finish, there are a lot of contenders. Some can take a punch; some bounce back fast. Here's how to choose the one that's a fair match for your project.
For many woodworkers, the contest to choose a finish ends in round one. Whether it's polyurethane, Danish oil, or spray lacquer, the winner never changes. But the finish you like best may not be the best one for your project, depending on its style and use.
All types of finishes have strengths and weaknesses, and a strength in one situation may become a weakness in another. For example, do you want a finish that's thin enough to apply fast and easily, or one that builds a thick, protective film in just a couple of coats? Should it be water- and chemicalresistant or easy to repair? Do you want a surface you can rub out to an even sheen or one that resists abrasion?
Clear finishes fall into six categories, each with its own mix of characteristics.
Drying oils, including boiled linseed oil and pure tung oil, penetrate the wood surface and react with oxygen to cure. Boiled linseed oil contains drying agents that let it cure overnight, but tung oil can take several days. Tung oil, however, darkens less with time. Beware: Some finishes with "tung oil" in their name contain little or no real tung oil as an ingredient.
Oil/varnish mixes, such as Danish oil, enhance grain while laying down a thin film. Because of their oil content, oil/ varnish mixes also need to dry overnight.
Lacquer combines nitrocellulose solids in a mixture of solvents to create a film finish that dries quickly and adds a faint amber tint. For a clearer finish, use cellulose acetate butyrate (CAB) lacquer. Unless you buy a formula that dries slowly enough to brush on, plan to spray most lacquers.
Water-based finish goes by many names that may include the words "lacquer" or "polyurethane," but most use acrylic or acrylic/polyurethane resins in solvent and water. By eliminating oil, and using acrylic and other clear resins, water-based finishes don't yellow as they age.
Wiping varnish, usually a type of polyurethane, comes premixed, but you can make your own by thinning regular varnish with mineral spirits.
Polyurethane varnish mixes alkyd and polyurethane resins with different types of drying oils. Unlike an oil/varnish blend, however, the ingredients are heated until they combine. Reducing the ratio of oil to resin creates a hard finish for indoor use. Increasing the amount of oil makes the finish flexible enough to withstand wood movement outdoors.
Now that you know the players, learn how to get the most from them.
On the following pages, we arranged these finish types with durability increasing from beginning to end. As durability increases, though, ease of repairs decreases. For example, lacquer offers little resistance to alcohol or water, but it's as easy to repair as spraying on a fresh coat. Polyurethane varnish ranks tops in moisture and chemical resistance, but repairing deep scratches requires stripping the old finish.
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