Clear Wood Finish: Varnish vs. Oil
There are many clear wood finishes on today’s market. Two of the most popular are polyurethane varnish and tung oil stain. While polyurethane is a synthetic material, tung oil stain is organic and made from the pressed seed extract of the tung tree. This article compares the two in terms of pros and cons, application and equipment, and maintenance and clean-up.
As a liquid plastic, polyurethane goes on, as opposed to into, the wood. It requires some skill to apply but can be used by novices if they do their homework. The end result is a durable, high-gloss, protective coating. This finish can be applied to both raw and newly stained wood or over older varnish if the wood is thoroughly sanded. Polyurethane is best for most exterior wood surfaces subject to moisture, fungus, or mold and is a must-use for any marine environment. It may require recoating as often as every year on items like boats, but in protected areas or indoors the surface can last years without reapplication. When used on furniture and cabinets, it can be maintained with a typical wax dust spray.
The biggest drawback for varnish is that it will eventually crack or peel, and water and mold can discolor the wood beneath.
Tung Oil Stain
But, your house is not a boat, right? Tung oil is used mainly on furniture, cabinets, interior doors, and trim and is very easy to apply, recoat, and maintain. It penetrates into the wood, so the finish will never crack or peel, unlike polyurethane. It has less of a gloss than varnish, but a more velvet-like feel and a visible grain. For maintenance, a dry rag wipe-down is enough, but never use a wax spray because it will prevent reapplication. A final great advantage is that it can be reapplied without sanding.
Polyurethane application requires a fine bristle brush designated for oil-based paints, paint thinner, a small pail with handle, lint-free rags such as old cotton t-shirts, a wire bristle brush, 220 sandpaper, and a lot of patience. In a sense, the varnish is like nitroglycerin in that it does funny things when agitated. Namely, lots of air bubbles. To avoid bubbling, use a plastic, snap-on pour spout for a one-gallon can. Transfer less than what’s needed into the cut bucket, as pouring the excess back into the gallon bucket causes more of those pesky bubbles. Focus the pour against the side rather than directly into the bottom.
Next, wet the brush minimally, brushing excess out on the lip of the pail. Using a dryer brush will help avoid drips and puddles. Hold it at a distinct angle with the handle closer to the wood and apply in long, even strokes. The first coat should be the thinnest of all, so don’t overdo it.
Use up all the varnish in the brush and lightly feather out any drips, puddles, or bubbles. Small bubbles may disappear while drying, but they can be sanded out before the next coat. Wait 24 hours between coats and remove any excess dust with a rag dampened in paint thinner before each new layer. Use a minimum of two thin coats instead of a single thick coat, as thin coats are essential to avoid cracking caused by exposure to sunlight and the elements. The final dried coat may be smoothed with superfine steel wool, number 0000, or synthetic steel wool to avoid any metal “filings” left on the surface, but stay away from sharp corners, concentrating on flat areas only. Again, a lot of patience and slow, light but long strokes are the keys to a good-looking finish.
Tung Oil Application
This is where tung oil shows its advantage. You will need a high-gloss tung oil, staining sponges (a small sponge covered with terry cloth), clean cotton rags, and a cut bucket. Depending on your surface, a blunt screwdriver covered with a rag to remove excess oil from tight corners is also useful.
To begin, pour the oil into the cut bucket. After wetting the sponge in the oil, squeeze most of the excess back into the bucket. Working quickly, wet a large portion of the wood, as much as possible in four to five minutes. Do not let tung oil dry more than five minutes before removing excess oil with one rag and then again with a second dry rag, polishing hard until the surface becomes slick. This hand rubbing is more important on the final coat than the first. Apply a minimum of three coats, allowing 24 hours between each. Almost no sanding is required if you’ve done your polishing well. Later coats can be applied at any time to renew the luster after light cleaning with a rag dampened in paint thinner.
Just before the final coat, for a silky, super smooth finish, very lightly sand flat areas with 440-grit wet or dry sandpaper from an auto parts store. Wet the paper with a minimal amount of oil before sanding.
For varnish brush clean-up, dunk the entire brush into paint or lacquer thinner in a clean bucket, working the brush against the bottom of the pail. Work the thinner through the bristles with fingers and a wire brush, concentrating at the base of the bristles. Repeat until the varnish is gone before doing a final clean with fresh thinner. Brush out the thinner on a clean board or piece of absorbent cardboard. Finish up by slapping the brush back and forth over a corner of a clean board, and work a dry rag through the bristles a final time. To clean the bucket, wipe it out with a rag and thinner, and give it a final wash with dish soap and warm water.
For oil clean-up, bag the oily rags and sponges in plastic and trash them. Clean yourself if needed with thinner, an ammonia-based window cleaner cuts the smell of thinner, dish soap, and water. Wipe the cut bucket dry.
And that’s why using oil is so much easier. No skills, less equipment, little clean-up, and no “hard brush in the morning” worries. However, no matter what finish you decide to use, good luck and remember that patience and hard rubbing pay off.