Finishing with Oil/Varnish Blends
hoosing a finish for your completed project is surely one of the most agonizing decisions you make. After all, a trip to the store reveals a dizzying display of oil- and water-based polyurethanes, as well as lacquers, shellacs, and acrylic finishes. But don't overlook the oil/varnish blends with names such as Danish oil, tung oil, antique oil, and others. These easy-to-apply blended finishes penetrate the wood, form a light film on the surface, and provide the feel and look of a "hand-rubbed" finish in a satin sheen.
What it is
An oil/varnish blended finish is generally a mix of boiled linseed oil (BLO), mineral spirits, and varnish or poly resins. Manufacturers adjust the proportions to affect sheen and hardness. BLO enhances the grain and color of woods such as walnut, cherry, and mahogany. But its tendency to darken over time may give lighter woods, such as maple or holly, a yellow cast, so choose a tung oil instead for light-colored woods [Photo below]. Check the tung-oil product label for phrases such as "contains mineral spirits" or "petroleum distillates." This indicates a blended finish rather than the far-slower drying pure tung oil.
The addition of polymerizing agents and chemical dryers causes BLO to harden when exposed to oxygen (a fact demonstrated when trying to unscrew the cap on the can the next time the finish is used). Adding mineral spirts or naphtha thins the BLO, allowing it to penetrate deeper into the wood; this solvent evaporates as the finish cures. Because the oil soaks into the wood, added poly or varnish resins improve durability and provide a bit of sheen.
Applying these finishes is pretty straightforward. Begin by sanding the project to 220 grit and removing any dust. Shake the finish well, then flood the wood surface with finish and maintain a wet surface for about 30 minutes to allow the mixture to penetrate deeply [Photo below]. Then, wipe all remaining wet areas with a clean rag.
Note that the finish's chemical driers generate heat as the finish cures, and the rag used to apply it may catch fire if left wadded up. Allow rags to dry out before discarding them [Photo below].
On open- or large-pore woods, such as oak, mahogany, and others, small rings or pools of finish may reappear after wiping [Photo below]. As the finish flows into the pores, air moves out, bringing a bit of finish to the surface after the initial wiping. Remove it with a rag. If you notice it after the finish cures, sand lightly with 400-grit sandpaper.
Give the first coat 24 hours to cure, then apply a second coat in the same way. On very porous woods, a third coat may be necessary.
During cool temperatures, warming the finish can in a pan of warm, not boiling, water reduces the finish's viscosity, allowing it to better penetrate into the wood.
Drying times are based on a 70-degree temperature and 50–70 percent humidity. A blended finish applied in warmer and drier conditions may become thick or gummy prior to the recommended reapplication time, making it difficult to wipe cleanly. Adding a bit of fresh finish (which contains mineral spirits) will soften the finish and make removal easier.
Because an oil/varnish blend doesn't provide much durability, consider a topcoat of a film-forming finish such as polyurethane, lacquer, or shellac [Photo below].