The Basics of Wiping Varnish
Of all finishes available, none offers as much protection and durability with as little difficulty in application as wiping varnish.
With wiping varnish you can achieve a run-free, brush-mark-free, air-bubble-free and almost dust-free finish, which after several coats is very protective against moisture penetration, and resistant to scratches, heat and solvents. And you can do this with no more effort than wiping or brushing on the finish, and either leaving it, or wiping off some or all of the excess.
No other finish offers all of these great qualities. The only finish that competes is gel varnish, but it’s messy to apply, and it can’t be built up as fast on the wood without leaving brush marks. Wiping varnish is arguably the single best finish for most amateur woodworking projects.
What is Wiping Varnish?
Wiping varnish is simply common oil-based varnish (any type, including alkyd varnish, polyurethane varnish or spar varnish) that is thinned enough with mineral spirits (paint thinner) so it is easy to wipe on wood. You can easily make your own.
The name, which I created in 1990, and which has been adopted by most writers and teachers of wood finishing, makes sense because the purpose of thinning is to make the varnish easy to wipe.
You may already be using wiping varnish and not realize it because it isn’t sold under that name (maybe because that would give away the simplicity of the finish). It’s sold under many different brand names, and few indicate what the finish really is.
This is the problem with wiping varnish and the reason it isn’t widely recognized as one of the best finishes for anyone not using a spray gun. Manufacturers obscure the true nature of the finish by their misleading, and sometimes outright deceptive, product labeling. They want you to think they are selling you something different and special.
In this article I will tell you about varnish, how wiping varnish came to be, how to make and identify wiping varnish and how to apply wiping varnish. I will also explain how wiping varnish differs from oil, and mixtures of oil and varnish. (See “Testing for Oil: Does It Get Hard?” on page 74.)
What is Varnish?
Varnish is a very common finish that is appreciated for its terrific moisture, scratch, heat and solvent resistance. No matter how new you are to woodworking, you have probably used some type of varnish or oil-based paint, which is varnish with pigment added.
One way to identify varnish is by the thinner and clean-up solvent listed on the container. This is mineral spirits, which is usually identified by its more all-inclusive name, “petroleum distillate.” The only other finishes that thin and clean up with mineral spirits are oil, blends of oil and varnish, and wax. None of these finishes cure hard, so they can’t be built-up thick on the wood like varnish can.
All types of varnish are made by cooking an oil with a resin. (This is done in controlled conditions; you shouldn’t try it yourself because of the fire hazard.) The oil, which is usually linseed oil, tung oil or modified soybean (soya) oil, makes it possible for the finish to cure in contact with the oxygen in air. The resin, which is usually alkyd or polyurethane, provides the hardness in the finish.
The most popular type of clear varnish is polyurethane varnish. It is the most protective and durable of the varnishes. That is, it is the most resistant to moisture penetration, and it is the most resistant to being damaged itself by coarse objects, heat or solvents.
Spar or “marine” varnish is also widely available. Its unique quality is increased flexibility created in the manufacturing process by including a higher ratio of oil to resin. Spar varnishes are meant to withstand the greater shrinking and swelling of wood placed outdoors. Sometimes this varnish contains UV absorbers to resist damage from sunlight.
If the varnish is not labeled “polyurethane” or “spar,” it is probably alkyd varnish. Alkyd is the workhorse of the varnish resins. Almost all varnishes contain some alkyd, including polyurethane varnish. Oil paints are almost always made with alkyd resin and are often simply called “alkyd paint.”
These are the common types of varnish on the market. You can thin any of them with as much mineral spirits as you want. The more mineral spirits you add, the less “solids” the varnish contains and the thinner each layer of finish will be on the wood. (In some parts of the country it is illegal to thin varnish because of VOC laws, and some brands of varnish reflect this by telling you not to thin their varnish; but you can’t harm any varnish by thinning it.)
No finish is perfect in every way, and varnish is no exception. Varnish has two critical flaws: It cures slowly, and it has a fairly thick or viscous consistency.
The slow curing gives dust a lot of time to settle and become stuck, and runs and sags have a lot of time to develop on vertical surfaces.
The thickness is responsible for brush marks and bubbles curing in the finish because it doesn’t flatten out well and bubbles don’t pop out easily.
As a result, varnish is actually the most difficult of all finishes to apply with near-perfect results. But there is a way around the problem: Thin the varnish so it cures faster (the thinner film combines faster with oxygen in the air), levels better and releases bubbles easier.
The product made by thinning varnish is “wiping varnish.”
History of Wiping Varnish
Wiping varnish has been very popular with amateur woodworkers and refinishers for at least 35 years, but few have actually known that it was wiping varnish they were using. The finish was made popular in the late 1960s and early 1970s by Homer Formby. He traveled the country doing demonstrations of his new miracle finish, “Tung Oil,” at shopping malls and antique clubs, and he made a number of infomercials that were broadcast on TV.
Few people were familiar with tung oil, which has its origins in China, so the exoticness of the name and source made the finish seem special. Formby was a master salesman.
But he wasn’t selling tung oil. He was selling thinned varnish that he labeled “Tung Oil Finish.” This finish is still available and the oil used to make the varnish isn’t even tung oil. It’s modified soybean oil.
It’s important to note that even if this finish were made with tung oil – that is, tung oil cooked with a resin to make varnish – it still wouldn’t be “tung oil.” It would simply be varnish made with tung oil instead of some other oil.
Formby made contact with a very large number of people, however, and his mislabeled wiping varnish was a very good finish. So he won a big following and created a market for finishes labeled “tung oil.” Soon other manufacturers joined in with their own “tung oils.” Some made their varnish like Formby did – by cooking alkyd resin with modified soybean oil. Others cooked real tung oil with one of the resins.
Some misunderstood what was happening and actually sold real tung oil in its raw state and this really created problems. Incorrectly labeled or not, thinned varnish is an excellent finish because it cures hard. Tung oil doesn’t cure hard, so it can’t be built up on the wood without being sticky and gummy.
Moreover, unlike boiled linseed oil, which will produce an evenly attractive satin sheen after just two or three coats, tung oil requires five or more coats to produce an equivalent satin sheen. And each coat requires several days to cure and then has to be sanded smooth before the next is applied. Tung oil is a difficult finish to apply effectively, and many people who have tried it have been very dissatisfied.
Despite the difficulties with real tung oil, the market for a thinned varnish finish had been established. So as time passed, other manufacturers marketed their own versions of wiping varnish. Unfortunately, many of the manufacturers further confused the marketplace by labeling their finishes with non-informative names such as Waterlox, Seal-a-Cell, Salad Bowl Finish, Val-Oil, Profin and more.
The result is that no one using one of these brands now knows what finish they are using if they do no more than read the label. But all of these brands, being wiping varnish, are easy to use, and they produce excellent results.
Make Your Own
You don’t, of course, have to buy pre-packaged wiping varnish. You can easily make your own. If you do, you can choose which type of varnish to use, polyurethane, spar or alkyd, and you can also choose between gloss and satin.
After choosing a varnish, turn it into a wiping varnish by thinning it with mineral spirits. (You can also use turpentine, but there is no advantage, and turpentine is more expensive and has a more pungent odor.)
To recreate a commercial wiping varnish, thin the varnish 50/50 with mineral spirits. To get a faster build, thin the varnish less. The less you thin the varnish, the more you increase the possibility of brush marks and bubbles curing in the finish. You also increase the amount of dust that can stick to the finish because a thicker film (after the thinner evaporates) takes longer to cure.
I suggest you begin with one part thinner to two or three parts varnish, and see how it feels to you. You can always adjust the ratio as you are applying the finish.