Varnish – durable, dependable, long-lasting

The recipe for a varnish consists of oil (such as linseed, tung or soybean oil), resin (usually a synthetic acrylic, alkyd or poly­urethane resin, and rarely a natural resin, such as copal or rosin), solvent (such as naphtha, acetone or mineral spirits) and one or more additives that can include dryers, anti-skinning agents, flatten­ing agents, ultraviolet stabilizers and anti-oxidants.

Go into any hardware store and you’ll likely see an array of “varnish” for indoor use: oil-based varnish, waterborne varnish, oil-based polyurethane, waterborne polyurethane and waterborne oil-modified polyurethane. It might seem confusing, but they’re all varnishes, though made from different recipes.

The proportion of oil in the recipe has a bearing on how dura­ble and flexible the cured finish will be. Using less oil makes for a harder, more durable finish, but it will have less elasticity. The type of resin affects the durability and stability of the finish. Synthetic resins, particularly polyurethane, are the hardest and most durable.

Wiping Varnish

This is any varnish that has been diluted with mineral spirits. You can buy a commercial blend or make your own using a non-critical ratio of 1:1 or 1:2 (mineral spirits to varnish). It makes the varnish easier to apply and quicker to dry. The more coats you apply, the more durable the finish will be once it’s cured. For projects that won’t be handled a lot, four or five coats should suffice. Otherwise, a dozen or more coats aren’t out of the question.

Oil/Varnish Blend

These finishes are sold under names such as Danish oil or antique oil finish. Essentially, they consist of varnish mixed with a penetrating oil (boiled linseed oil or tung oil) and mineral spirits. You can make your own using a non-critical ratio of 1:1:1. An oil/varnish blend is more dura­ble than wiping varnish but takes a bit longer to dry.

Product Names

Sometimes product names can be confusing. “Polycrylic,” a brand name owned by Minwax, is a waterborne finish comprised primarily of acrylic resin. “Varathane,” a brand name from Rust-Oleum, con­sists of a product line that includes oil-based and waterborne finishes, stains and conditioners. Tried & True’s “Varnish Oil,” which contains polymerized linseed oil and modified pine sap, is strictly not a film fin­ish, but a penetrating oil finish.

Shellac – develops a beautiful patina over time

There seems to be a certain mystique associated with shellac. Perhaps it has to do with “French polish,” the traditional technique for applying shellac. Or the smooth gloss-like finish that gives an exceptionally deep luster. Whatever the reason, shellac is a versatile finish made from a natural resin secreted by the female lac beetle. The resin is processed into flakes that are dissolved with alcohol to form a fast-drying, moderately wear-resistant finish with excellent water and moisture resistance, but susceptible to damage from alco­hol and heat.

Shellac has a short shelf life (whether premixed or mixed in your own shop). Fortunately, it’s easy to dissolve shellac flakes as needed with alcohol (isopropanol, methyl hydrate or ethyl alcohol) in a mixture called a “cut.” A typical one-pound cut consists of one pound of flakes dissolved in one gallon of alco­hol (or any proportionate ratio, such as 1/4 pound to one quart). Flakes are available in a range of sheens, from clear (super blonde shellac) to rich, darker reddish brown (garnet shellac). Choose dewaxed shellac especially if you plan to top coat the shellac finish with polyurethane or lacquer, as neither will bond well to waxed shellac.

Shellac is easy to apply and repair, and buffs (or rubs out) to a wonderful finish. You don’t have to sand between coats of shellac unless there are bumps caused by dried dust on the surface. If you need to colour-match the wood, you can add an alcohol soluble dye to shellac or you can stain over the shellac.

Sources: leevalley.com; woodessence.com

Lacquer – unsurpassed clarity, quick drying, super hard

Lacquer has been a preferred finish in production shops for decades because it dries so fast when sprayed, can be easily buffed to an even sheen, takes pigments and dyes very well, and is easy to repair. While brushing lacquers are available, they’re not nearly as popular as the other film finishes.

There are nitrocellulose, acrylic and waterborne lacquers. Most brushing lacquer is made from nitrocellulose (a celluloid made from cellulose and nitric acid), solvents (naphtha, xylene, toluene and others) and plasticizers that make the nitrocellulose less brittle.

Like waterborne finishes, lacquer dries quickly and crystal clear. Unlike most other finishes, lacquer is self-levelling, which makes it somewhat easier to brush. As with shellac, there’s no need to sand between coats, it rubs out to a wonderful luster and is easy to repair. While lacquer is a durable finish, it’s less resistant to scratches, heat and solvents than polyurethane.

You should always wear a respirator equipped with an organic vapor cartridge when brushing lacquer or cleaning your brush with lacquer thinner, as both have a high VOC content.

Sources: minwax.ca; myoldmasters.com; rustoleum.ca (Watco); saman.ca

Waterborne – transparent, quick drying, durable

Waterborne finishes have become very popular over the past few decades, in part because they dry clear and don’t yellow much over time (though some include an amber cast that mimics the traditional oil-finished look). They dry very fast (with little time for dust to dry on the wood surface), clean up quickly with water, and provide very good wear, water and water vapour resistance. However, because they dry so fast, they’re somewhat more of a challenge to brush than varnish. You can add pigmented dyes directly to waterborne finishes, or stain or dye the wood before applying the finish.

You might get a bit confused when you see the term “water­borne” combined with “varnish” or “polyurethane” on the same container, as with Saman’s “Waterbased Varnish.” Waterborne finishes are coalescing finishes. Similar to oil-based finishes, they contain a resin (acrylic, alkyd or urethane) along with a much smaller amount of solvent and water as a carrier. After you lay on a coat of waterborne finish, the water evaporates more quickly than the solvent. The solvent softens the resin so that it bonds into a continuous film.

Depending on the type of resin used, waterborne finishes may be referred to as “water-based varnish,” “water-based lacquer” or “water-based polyurethane,” or simply as a “water-based” wood finish.

Waterborne finishes do raise the grain of wood, usually right after the first coat has been applied. Following coats don’t tend to raise the grain at all. Light sanding between each coat abrades the surface for the next coat to go on more smoothly. Along with shel­lac, waterborne finishes are the safest to use—they have negli­gible VOC levels, no toxic additives, are virtually odour free and are non-flammable. And, as environmental restrictions become tighter, it’s likely that waterborne finishes will become much more popular in the future. (see “Waterborne Finishes”, Oct/Nov 2019)

Sources: generalfinishes.com; minwax.ca; myoldmasters.com; rustoleum.ca; saman.ca; woodessence.com