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Finishes are used to seal, protect, and beautify wood. Two popular finishes are shellac and varnish. In this article, we’ll review the qualities and properties of both shellac and varnish.
We’ll also explain the similarities, differences, and the major distinguishing factor between these finishes. Finally, we’ll tell you when to use shellac, when to use varnish, and which is better.
What Is Shellac?
Shellac is a wood finishing product that is created when resin from the lac beetle is combined with denatured alcohol. Premixed shellac is available from any hardware store. A more cost-effective solution that allows you to control the viscosity of your shellac is mixing it at home.
The amount of resin in a shellac mixture is referred to as the ‘cut’. A two pound cut is the most common store-bought concentration, and contains two pounds of resin dissolved in one gallon of denatured alcohol. Thinner cuts can be achieved with store-bought or homemade resin by adding more denatured alcohol. To thicken homemade resin, you can add more resin flakes or discs.
Shellac is usually applied to wood with a pad, although brushes can be used to coat carved wood. Never use foam brushes to apply shellac, as they will be dissolved by the denatured alcohol. Shellac dries within seconds of application.
However, adding more shellac to the same area dissolves the coat underneath, making this one of the most forgiving wood finishes for splashes and drips.
It is used to beautify wood, enhancing and displaying the natural grain patterns.
Shellac application is best done within a narrow range of weather conditions. To speed dry time in a cold environment, use a fan to increase circulation. On humid days, you may need to add a dehumidifier to your workspace.
Shellac dries to a glossy sheen. If a matte finish is preferable, steel wool can be used to dull a shellac finish.
What Is Varnish?
Varnish is made from resin, which is heated in a base of oil or water and then combined with a solvent. It dries when exposed to air, as the solvent evaporates. Varnish can be applied with a brush, sprayed with compressed air, or wiped on with a rag.
It is typically used to seal and protect wood. Some varnishes are better for interior use, while others can hold up to weather and sun for use in exterior applications.
Varnish is built in layers. The first coat seals the wood. Each coat of varnish must be lightly sanded with fine grain sandpaper and cleaned of dust before another coat can be added.
Full-concentration varnish is usually only used as a top coat. For the middle coats, varnish is diluted with a solvent, usually mineral spirits.
While varnish is one of the oldest wood finishes, modern science has improved upon the original formulations. Acrylic resins can be used to achieve a hard, high-gloss varnish finish that will not yellow with age or sun exposure. Catalyzed varnishes change the drying process with the addition of a chemical catalyst, resulting in harder, more durable protection.
Varnish vs Shellac
On the surface, varnish and shellac appear very similar. Even experienced woodworkers can’t usually tell shellac from varnish just by looking at it. While these two finishes may have a lot in common, there are distinct differences as well.
Varnish and shellac can be applied to almost anything, contain similar ingredients, provide comparable levels of protection, and look similar when dried or cured.
Both shellac and varnish are resin-based finishes. Resins are thick, viscous liquids that can be found in nature or generated synthetically. Varnish typically includes urethane, alkyd, or phenolic resin. Shellac exclusively uses resin secreted by the lac beetle, a subtype of alkyd resin.
Another ingredient category shellac and varnish share is the inclusion of a solvent. Solvents are distinguished from thinners in that they don’t just move the molecules further apart, but actually change the bonds between molecules. Both varnish and shellac dry due to the evaporation of the solvent.
However, because of the different chemical compositions of these two finishes, they react to different solvents. Mineral spirits are a solvent for varnish, but will not dissolve shellac. Acetone will dissolve either substance. Denatured alcohol quickly dissolves shellac and will also dissolve varnish if given enough time to work.
One of the primary reasons to apply a finish to wood is to protect it from damage. Damage can come from sunlight, moisture, impact, or even pests.
Both shellac and varnish will help seal the wood, providing some protection from moisture. Both will protect the wood from scratches, scuffs, and dents, although varnish can withstand greater abuse than shellac.
Shellac and varnish are equally effective at discouraging pests. UV absorbing ingredients can be added to varnish, but shellac does not usually contain this protection from sunlight.
Shellac will stick to anything, and anything will stick to shellac. You can shellac over stain, paint, or bare wood. You can also paint or stain on top of shellac. You can even form a glaze effect by sandwiching a stain between two layers of shellac.
Varnish is nearly as versatile and can be applied over all wood stains, although some sanding is usually needed to prepare the surface. Oil-based varnish can be applied over acrylic or oil paint. To paint over varnish, a primer is necessary.
Both shellac and varnish can be used to build a lustrous clear finish that shows off the character and grain of the wood underneath. You can also add tint to shellac or varnish to add color to your finished wood piece. Shellac and varnish can be finished to a mirror gloss, or dulled to reflect less light.
While there are many similarities between shellac and varnish, there are important differences as well.
The differences between varnish and shellac start with it’s ingredients. While varnish is resin cooked in oil with a solvent added, shellac is resin combined with a solvent — no oil involved. Shellac is therefore quite thin in viscosity, and dries in seconds when applied to wood. Varnish usually needs to be diluted with a thinner to be applied, because it is very thick.
One of the ways to evaluate finishes is by the amount of VOCs (volatile organic compounds) they release. The EPA regulates VOC emission in consumer products, requiring a VOC rating to be included on the packaging for all home finishes. A low VOC rating generally indicates a safer finish — but not always.
Shellac has a VOC rating on the higher end of the scale. However, the off-gassing period is very short. VOCs are released as the solvent dries, and shellac dries so quickly that exposure is minimal. In fact, shellac can be considered non-toxic when dry, and is so mild that it is safe for use as a food glaze if properly formulated.
The maximum amount of VOC varnish can contain is set at 450 grams per liter. Oil and conversion varnishes usually come close to that maximum, while water-based varnish can be as low as 200 grams per liter. However, varnish lasts a long time without needing to be reapplied. Selecting varnish over a shorter-lasting finish may reduce your overall exposure to VOCs.
Shellac is a self-correcting finish. As long as you apply shellac in one direction in thin, even strokes without back brushing, each layer will dissolve the one underneath it. This makes it easy to deal with drips and achieve a smooth, even, shiny finish.
Varnish is not self-correcting. Imperfections must be avoided during the process of applying varnish, and sanded out before applying another layer. It is also much stinkier than shellac. Where shellac dries in seconds, most varnishes take hours or days to dry, and may take weeks to fully cure.
Properly applied and cared for varnish finishes can last up to 20 years. Once they start to yellow, crack, or peel, there’s not much that can be done beyond stripping the varnish finish and reapplying.
Shellac finishes start to degrade more quickly, but unlike varnish, it can be revived due it’s self-correcting properties. A mixture of one part shellac and four parts denatured alcohol applied to the finish should revive even cracked or bubbling shellac.
You can also choose to remove shellac and then apply a different finish.
Major Distinguishing Factor
The major distinguishing factor between varnish and shellac is that varnish cures as it dries while shellac does not.
Curing is a chemical hardening process that makes varnish a more durable, long-lasting finish than shellac.
However, because shellac does not cure, this type of finish can easily be revived when it starts to degrade. Varnish must be stripped and reapplied.
When to Use Shellac
Use shellac for interior furniture.
Varnishes are notoriously pungent, and the odor takes a long time to dissipate. During that time, VOCs are off-gassing into your home. Shellac dries quickly with minimal odor or off-gassing.
If you have a fine dining set or heirloom china cabinet that needs protection, shellac is definitely the best option. You can revive the finish as many times as necessary, extending its life. Because these pieces are treated gently by default, the superior damage protection of a hard varnish finish is not necessary.
Shellac should also be your finish of choice whenever your goal is to lock in odors. When underused, wood furniture gets musty. Dresser drawers are notorious for passing on that musty smell to fabric stored inside them. You can prevent this transference by sealing the odor into the wood with a few coats of shellac.
When to Use Varnish
Use varnish for exterior applications, and interior wood that will take a beating.
Because varnish gets harder as it dries through a process called ‘curing’, the protective barrier it forms over wood is more resistant to damage than the protection provided by shellac. Wood floors and trim are likely candidates for varnish use indoors.
Varnish can also be used to waterproof wood, making it impervious to the elements. Spar varnish and marine varnish are two formulations that contain significantly more oil than other varnishes, which helps them flexibly adapt to temperature and moisture-related changes in the wood.
Which is Better, Shellac or Varnish?
Many people feel more comfortable applying varnish because it is so similar to paint. Shellac can seem daunting and unfamiliar. However, when applying varnish, you must sand the entire surface of your project between every coat.
Shellac requires no sanding between layers, self-corrects, dries quickly and emits relatively few VOCs, making it the better choice for almost any project.
The exception would be outdoor furniture. Shellac is water-resistant, and can avoid absorbing water for up to four hours, but the finish may become cloudy where the water stood. If water penetrates the finish, rot can occur. Varnishes formulated for exterior use are unaffected by water, making it the superior choice for outdoor applications.