By Barb Skivington for Real Girls Create
There are many clear protective coating products on the market, formulated from numerous polymers, solvents, and additives. They are often classified as a shellac, varnish, polyurethane, or polycrylic. While these terms are commonly used to reference a final finish in general, these products are not the same, nor should they be used interchangeably.
Shellac is a natural product (made from the secretions of the lac beetle) that is available in clear, amber, and pigmented (white) formulations, although clear shellac is the favored choice as it is non-toxic, food safe, and safe to use on children’s items once dried and hardened. On existing pieces of furniture, it is used to block tannins, stains, and odors before painting. It can also be used to protect new finishes, and very fine furniture is often finished with clear shellac using a technique known as “French polish.” Shellac can be affected by heat (i.e., leaving white rings from a hot mug) or household chemicals, so a kitchen tabletop might not be the best place to use it for a final protective coat.
Essentially a plastic in the form of a liquid until it dries, polyurethane is available in both water- and oil-based formulations and comes in sheen varieties from dead flat to gloss.
Water-based polyurethane, known as polycrylic, is popular because of its low odor, low toxicity, and easy clean up. It goes on clear without adding a slight yellow color and dries fast. As with shellac, a polycrylic does not hold up well to heat and household chemicals. It’s good for surfaces that won't be exposed to heavy wear and tear.
Polycrylics do not always work well over matte paints. The additives in a matte paint keep the polycrylic from drying at its normal rate, often leaving behind cracks once dried. It can be difficult to use on larger pieces because it dries quickly. A polycrylic should always be applied in very thin coats; over darker colors it can give a milky finish if applied too thickly. Once you have applied a coat, you should avoid going back with a brush or roller to smooth as this can make your surface a rather untidy mess.
Oil-based polyurethanes are slightly more durable than their water-based counterpart, especially when it comes to handling heat. It will create a yellow or amber hue, especially to light colors. When working with a polyurethane, use a respirator in a well-ventilated area; polyurethane is highly flammable and toxic. Care should be taken with the disposal of leftover materials and rags. Polyurethane takes much longer to dry and cure than a polycrylic, so plan accordingly and follow the manufacturer's directions.
Varnish is used often in wood finishing but also looks beautiful over painted finishes. Varnish finishes produce sheens from dead flat to semi-gloss (through the addition of "flatting agents”) to gloss. There are two formulations of varnish available, oil-based and water-based.
Oil-based varnishes are often applied over wood stains as a final step to achieve a film for sheen and protection. They are thought to give wood more depth and color because they are actually absorbed into the wood surface, while the water-based version dries on the surface. Oil-based varnishes take longer to dry (as long as 24 hours for each coat) and several days to fully cure. They are not as popular as water-based varnishes because they are somewhat difficult to apply, and they have an odor.
Spar varnish, a form of oil-based varnish, is good for outdoor projects and for raw wood used for exterior doors and trim on rustic homes. In addition to protecting the wood, it also provides natural ultraviolet light protection.
As with other oil-based products, use a respirator and apply in a well-ventilated area. Care should be taken with the disposal of leftover materials and rags. Always follow the manufacturer’s directions.
Water-based varnishes, on the other hand, are easier to apply, dry quickly, and have very little odor. When applied over raw wood, grain raising may happen that requires you to sand after the first coat with fine grit sandpaper. For water-based varnishes, hardening or “curing” takes place as soon as the water has fully evaporated. They are typically more expensive than their oil-based counterparts. Water-based varnishes are good for commercial/high traffic areas where durability is important.
Use the following information when working with any clear protective coating product:
It is highly recommended that you spend some time experimenting with different clear coat products to test their compatibility with your underlying materials and to get a feel for how they brush, roll, sand, and polish. Always follow the manufacturer’s directions. Read the labels carefully and, if needed, consult with the manufacturer to learn more about their product, including its formulation, the number of coats required, dry time, and cure time.
Permission to publish this article given expressly to 3PaintGirls by Barb’s estate.