Wood finishing involves the application of a protective layer to otherwise bare wood. But before a protective coating can be applied, the wood’s surface must be prepared. Sanding, planing, and scraping can help eliminate surface imperfections by softening and smoothing the wood. Processes to alter the wood’s color and aesthetic are often applied before the finish, including staining and bleaching. Once these processes are completed, the appropriate finish is selected. However, because wood is a versatile material with countless functions, wood finish is equally diverse. By comparing specific application requirements with various finish traits, the right coating can be selected.
Types of Wood Finish
When selecting a wood finish, there are a range of characteristics to consider. Do you want the final product to shine? Or are you more interested in a matte appearance? Is the application intended to withstand outdoor use? Or is durability not a concern? Prioritizing finish traits can simplify finding the appropriate coating. Some common types of clear finish and their distinguishing characteristics are discussed below.
One of the perks of opting for a wax finish is that it’s easy to use and apply, and it produces a nice shine. However, wax finishes often need to be reapplied and only provide minimal protection. They are easy to remove, which makes it a fairly noncommittal finish selection.
Although shellac is classified as a clear finish, some grades carry a distinct yellowish tint. Shellac does, however, provide its substrate with moderate water protection and provides effective protection against solvents, with the exception of alcohol. The coating itself is durable and does not require reapplication. The application technique can be complicated but, like wax, shellac can be completely removed using alcohol. Additionally, shellac is compatible with other coatings and acts as an effective base layer.
This clear coating creates a hard, glossy finish, which provides good substrate protection and has strong durability. However, there are several toxic solvents in the mixture, requiring the applier to use a protective mask to avoid inhaling toxic fumes. Additionally, the coating typically requires a spray-on application method, which further releases toxins into the air. Alternative brush methods can be used to avoid this complication. Like shellac and wax, nitrocellulose lacquer can be removed.
In many ways, conversion varnish resembles nitrocellulose lacquer. Both coatings result in hard, glossy finishes and are durable. Their application methods are similar, and in both cases protection against toxins is necessary. Conversion varnish, however, can only be applied in shops using specialized spray equipment and is hard to remove. Additionally, the coating can resist an array of substances, providing strong substrate protection.
Like other varnishes, polyurethane varnish delivers a clear coating. However, multiple layers can give a substrate a plastic type finish, which provides strong protection against an array of substances. Because the solvents involved are petroleum-based, the coating is relatively safe. The coating can be somewhat difficult to apply and requires a 30 day curing period. Paint removers can effectively remove the coating, and after the curing period, the coating is quite durable.
Due in part to the addition of water, water-based polyurethane produces a clear coating without the plastic look. Additionally, it works well on products that are exposed to UV and is safer to use than traditional polyurethane varnish. The coating dries rapidly, so care must be taken in brush and spray application. The curing period is the same as polyurethane varnish, after which the coating is durable. Paint removers also work to remove water-based polyurethane.
Oil finishes, such as tung oil and linseed oil, can be used to accentuate the wood’s grain but do not provide much protection. They provide the wood with a warm glow and increase in durability when layered. Application is easy, but drying typically takes 12 hours or longer. To remove oil finishes, the substrate must be sanded down because oil absorbs into the wood.