For years, the word “varnish” has been used as a generalized term to describe many kinds of wood coatings, including shellac, lacquer, and polyurethane. However, though there are many different types, varnish is a specific product rather than a generic term or grouping of other types of products.
Varnish vs. Polyurethane
Types of Varnish
Varnish got its start as a mixture of sap (resin) and alcohol (solvent). Nowadays, there are many different types of varnish that have been created to serve a variety of different purposes. This process of creating new varnishes is simply done by manipulating the ingredients that go into a varnish—resin, solvent, and oil—as well as the ratio of the ingredients present in the mixture. Listed here are the most common types of varnish, as well as what distinguishes them from one another.
Spar Varnish
A spar is a strong rod, typically made of wood, that supports the sail on a ship. Spar varnish, or yacht varnish, is a traditional type of varnish used to protect the spar and other wooden parts of a boat or ship that are highly prone to damage from the elements. Because of its intended use, spar varnish was, historically, very flexible but not very durable. However, modern versions of spar varnish have been altered to be more durable, more UV-resistant, and more attractive in appearance.
Exterior Varnish
Exterior varnish is an example of modernized, modified spar varnish. Sometimes labeled as spar urethane, it differs from true varnish. Exterior varnish possesses the protective, flexible characteristics of spar varnish, but has been modified to be UV-protectant and more durable, thanks to its slower curing time.
Alkyd Varnish
Alkyd varnish is a highly versatile varnish that can be used both indoors and outdoors. The word “alkyd” refers to the alkyd resins in the varnish, which are polyester resins modified with fatty acids commonly derived from vegetable oil. Many alkyd varnishes offer great UV protection, quick-drying, yet durable finishes, and a clear appearance that greatly enhances the beauty of the wood.
Bituminous Varnish
Bituminous varnish, or black varnish, refers to any type of varnish in which the resins are replaced with bitumen (petroleum-based hydrocarbon). The main purpose of black varnish is to coat ironwork, protecting it from corrosion.
Acrylic Varnish
Acrylic varnish is a water-based protective coating that is far from traditional varnish in its makeup. Because it’s highly transparent, easy to apply, and anti-yellowing, the most common use of acrylic varnish is as a protective coating applied over the top of paintings.
Oil Varnish
Though it’s debatable whether or not oil varnish is a true varnish, it is commonly referred to as such. Oil varnish is simply a mixture of resin and drying oil, absent of a solvent. This results in a finish that penetrates deeply into the wood and hardens over a very long period of time.
Spirit Varnish
Similarly to oil varnish, it’s debatable whether or not spirit varnish is a true varnish. While oil varnish is a mixture of resin and drying oil, absent of a solvent, spirit varnish is a mixture of resin and a solvent, absent of oil. Spirit varnish is quick-drying and highly polishable, but not nearly as durable as oil varnish.
Safety Considerations
Regardless of which type of varnish you’re using, you should only do so in a well-ventilated environment and while wearing a respirator rated for fumes. Not all varnishes are created equally, and before you choose one and use it on your project, pay special attention to its intended uses. For instance, using varnish with a weeks-long cure time that releases a high amount of VOCs (volatile organic compounds) in a space that you or anyone else frequents will pose great risks to the health of those exposed.
How to Use Varnish
The following steps will outline the process of varnishing a flat wood surface using alkyd varnish. These steps will vary depending on the item you wish to varnish and the type of varnish you choose.
How to Care for Varnished Wood
Maintaining varnished wood surfaces and keeping them free of debris generally only requires an occasional wipe down with a dry, soft, lint-free cloth. In the event that there is stubborn, grimy residue, using a lightly damp cloth to free the residue may be necessary and should be immediately followed up with a dry, lint-free cloth. To bring out the shine of a varnish surface, a furniture polish that is specified safe for varnish will do the trick.
When to Replace Varnish
If the varnish on a piece of furniture or other wooden item is looking worse for the wear, it may be time to strip it and replace it. While some people advise adding new varnish overtop of existing varnish, this likely isn’t a good idea in most cases. It is better to strip the varnish using a stripping gel or sandpaper, or a combination of the two, then prep the surface and apply new varnish.
