The start of a great finish
He wrote Understanding Wood Finishing, a book that has sold more than a quarter of a million copies; he's the editor of Finishing and Restoration magazine; and he teaches at seminars across the United States. So who better than Bob Flexner, to list some of the essentials of finishing and refinishing?
Bob operates a furniture restoration shop in Norman, Oklahoma. He became a member of WOOD® magazine's Woodworking Hall of Fame in 2000.
- There are only three tools used to apply finishes: Spray guns, brushes, and rags. You can use any one of these tools with any type of finish.
- Products sold as "sanding sealers" don't seal the wood any better than the first coat of any finish. Sanding sealers just make sanding easier.
- Dye dissolves, so it penetrates into the wood everywhere the liquid does. Pigment suspends and settles, so pigmented stain lodges only in pores and scratches that are big enough to hold it.
- The thinner you make any finishing product, the easier it is to apply. But thinning reduces the film build, so you might have to apply an extra coat or two.
- The basic rule for using a spray gun: Keep the gun moving while the trigger is pulled. (Pull the trigger before you swing the gun over the wood, and release it after passing the other edge.)
- Finishes bond to one another in two ways: chemical and mechanical. Chemical bonding occurs when the applied coat dissolves into the existing coat of the same, or similar, type of finish. For example, thinned lacquer will dissolve into lacquer or shellac. Mechanical bonding is made possible by scuffing a surface with an abrasive; it's required when the new coat is not likely to dissolve into the existing surface. Varnish needs to be scuffed before you add another type of finish, or even another coat of varnish, if the original coat has had time to cure thoroughly.
- A finished or painted surface must be clean and dull for successful recoating. Clean it with soap and water; clean it further and dull it by rubbing with steel wool or sandpaper or washing with tri-sodium phosphate (TSP), ammonia, or alcohol.
- Varnish in a different room than the one where you sand, if possible. Otherwise, let the dust settle, then wet-mop the floor so you don't kick it up again.
- Hit the brush against your hand to knock out any loose bristles.
- Wipe the wood with a tack cloth just before you start brushing on the varnish.
- Whenever possible, reposition the piece as you work so the area you're varnishing is horizontal. Varnish the most important surface (usually the top) last.
- If you have trouble with air bubbles remaining in the finish and not popping out, thin your varnish with 10 percent to 20 percent mineral spirits.
- Always position your workpiece so light bounces off the surface toward you, so you can see any runs, sags, or other flaws, and remove them as you work.
- Stains that clean up with water are water-based; they'll raise the grain of the wood. Before applying them, wet the wood; let it dry overnight, and sand it lightly with fine, used sandpaper.
- Use gel stains to reduce splotching on such woods as pine, birch, and cherry.
- If a piece includes both plywood and solid wood, stain samples of both to check the color. Veneered plywood usually turns out lighter because the glue under the veneer blocks deep penetration, so it needs more stain to match the solid wood.
- Be sure to wipe off the excess after applying oil to the wood. That step is especially important when you use straight linseed oil or straight tung oil—they cure slowly and stay soft.
- Many "oil" finishes are varnish thinned with mineral spirits, and more accurately are called "wiping varnish." Some are blends of oil and varnish. Choose a wiping varnish if you want to build a glossy finish; choose an oil/varnish blend to produce a satin look with little build.
- To figure out which type you have, pour a small amount on a piece of glass and let it start to cure overnight. An oil/varnish blend will appear wrinkled the next day a wiping varnish will be smooth.