For aspiring woodworkers, choosing the right finish can seemingly be a difficult task at least at first. This is because the most popular types of topcoats, varnish, lacquer, polyurethane, and shellac have advantages and disadvantages which makes them best suited for particular types of settings.
When I started, I knew little about all four types of topcoats, and worse, I didn’t understand the difference between a topcoat the cures and one that evaporates. This is an important distinction that needs to be understood before choosing the right product.
What is Curing?
A curing finish is one that is performed by a chemical reaction and not when the solvent evaporates from the product. Varnish for example using a curing finish because it contains alkyd, polyurethane resin, or both that create a chemical reaction when applied to the surface. The result is that the product hardens or cures.
Lacquers and shellacs on the other hand contain solvents such as water that evaporate once exposed to the air. This means that as the product is being applied, it is drying at the same time. While this makes lacquers and shellacs somewhat less durable, they are far easier to repair in terms of removing scratches, dings, and other imperfections in the topcoat.
What follows are the four most popular types of topcoats, including their individual advantages and disadvantages.
What is Varnish?
While varnish is a specific product, the term has also been used as a catch-all name to describe various topcoats made from lacquers, polyurethane, shellacs, and more. This makes it difficult at times for aspiring woodworkers to identify varnish from other topcoats that are crafted from different materials.
The actual varnish is made from an alkyd resin that is combined with a solvent which, when it cures allows the varnish to harden. It should be noted that the curing process of varnish differs from the evaporation used for lacquer.
In most forms, the varnish is similar in some ways to polyurethane although it does lack some of its attributes. Varnish tends to have more oil in it which makes the product easier to apply under certain circumstances.
Benefits of Varnish
Arguably the most important benefit that varnish has to offer is that it may be the best topcoat for wood surfaces that sit outdoors. This is because the varnish is highly resistant to ultraviolet or UV rays which tend to break down other types of topcoats. Other advantages include the following.
- Heat resistant
The heat resistance is most notable outdoors where the hot, humid summers are withstood better by varnish that most, if not all other topcoats.
There is really no single issue with varnish except in comparison to polyurethane. In other words, varnish is durable, but not as durable as polyurethane. Pretty much all the advantages save for its suitability on plywood furniture or wooden surfaces outdoors are found within polyurethane topcoats. This means that varnish is best considered for surfaces that will see plenty of exposure to the sun and the elements.
What is Lacquer?
The story of lacquer is divided into two parts. There is natural lacquer that dates back to the Neolithic Age. In other words, more than 7,000 years which predates most civilizations. Made from tree sap, most notably the Toxicodendron vernicifluum or the Chinese lacquer tree, this product was first developed right at the end of what is commonly known as the Stone Age.
However, the lacquer that most people know about today was first created in the 1920s. This is a synthetic version that improves over the natural type in different ways. It is quite popular as a topcoat because of its inherent strengths.
Advantages of Lacquer
The modern version of lacquer has strong advantages that make it quite desirable for use as a topcoat for most wood surfaces.
- High gloss finish
- Impervious to most liquids
- Fast drying time
The last advantage of lacquer, being clear and colorless helps make it quite popular as it brings out the natural beauty of the wood underneath. Keep in mind that the clarity only works on certain types of wood. There are types of wood in which lacquer may reduce the depth and 3D effect when viewing the surface.
Despite all its attributes, lacquer does have one considerable drawback that needs to be addressed. It is created with a large number of VOCs or volatile organic compounds that are toxic and dangerous when in its liquid state.
When the lacquer is applied, a respirator needs to be worn to prevent the VOCs from entering the lungs. A standard mask will not work, and the application process needs to be performed outdoors or in a well-ventilated area. Keep in mind that when the lacquer is fully dried, the VOCs are for the most part trapped. However, small amounts of VOCs may leak into the atmosphere which may build up over time inside the home.
What is Polyurethane?
Polyurethane may be the most abundant of all products that are used as topcoats for wood and most types of plywood. Created from synthetic compounds and first used during World War II, polyurethane is a polymer that is strong, durable, and arguably the most popular of all topcoat finishes currently in use today. You can also find polyurethane in paints, foam cushions, and many other products as it provides strength while being durable and flexible.
There are two basic types of polyurethane finishes, oil-based or water. It would not be accurate to call the water version of polyurethane water-based since the presence of the H2O is quite limited. But the addition of water means that the polyurethane dries quicker which means less time from application to finished product.
Benefits of Polyurethane
- Relatively inexpensive
- Wide variety of colors and tints
- Fast drying for water versions
As a top coat, it is the hardest and lasts longer than any other product on the market today. This means that almost all woodworking shops will have cans of polyurethane around to be used at the topcoat. The fact that it is relatively inexpensive helps with its popularity as well.
If there is one drawback, it is that most polyurethane products have volatile organic compounds or VOCs present. This means that the application process will need to be performed while wearing a respirator and do the work outdoors or in a well-ventilated area.
However, there are polyurethane products that have fewer VOCs present and they are usually labeled as such. This means that you can wear a mask instead of a respirator, but the work will still need to be performed in a location that has plenty of air-flow to disperse the VOCs.
What is Shellac?
Created from the dried secretions of the Lac beetle, this natural product is dried and processed so that it can be transformed into shellac through the use of a solvent which is most often alcohol. Once it has been prepared, the shellac is ready for wood. Once the shellac is fully applied, the solvent will evaporate and leave behind the product which protects the surface of the wood.
Although the origins of shellac are not fully known, it was in the late 16th century that it started to enjoy widespread use. So popular in fact that a separate profession was created to distinguish a varnisher from a woodworker. Although the two professions have basically merged once again, the popularity of shellac is still ongoing.
Shellac has enjoyed a long run as a popular topcoat for wood. From the late 16th century up until the 1960s when synthetics products became widespread in their use.
Benefits of Shellac
There are good reasons why Shellac, despite being less popular today than in its prime, is still in widespread use.
- Colors and tints can be added
- Hold its color or tint for a long time
- High gloss finish can be obtained
There is also its availability as shellac is a staple of wood finishing products.
Disadvantages of Shellac
However, with all its attributes shellac does have some issues.
- Alcohol soluble
- Heat creates discoloration on a dried surface
In other words, if I spill my beer or set a cut of hot coffee onto a tabletop that has a shellac topcoat, it will either dissolve or discolor the shellac. This is why shellac is generally not used for tables or any surface in which a hot item might be placed.
Choosing the Right Topcoat
Once I’ve finished my woodworking project, it becomes time to choose the right type of topcoat. With four excellent products to choose from the decision may not be easy in most circumstances. However, it does pay to understand the advantages of what each topcoat offers along with the setting that my woodworking project will be located once a topcoat has been applied.
What follows combines frequently asked questions about topcoats that put in order which ones are best for that particular use.
There is no real winner when it comes to which product is the easiest to apply. That is because, in their wet states, the application is quite simple. It is true that I can spray either polyurethane or lacquer from the can which means I can cover a larger area faster. But wiping on the product with smaller surfaces is nearly as fast.
If I want the beauty of the wood to show through, then lacquer is the best for the job. It has unmatched clarity to bring out the details in most wood surfaces. Polyurethane with water is a close second and often a good choice thanks to its low cost. But lacquer still works better for me.
When my goal is to apply a topcoat that will last for the longest time, polyurethane is the one I choose. This is because polyurethane is both flexible and strong which makes it longer lasting compared to all other topcoats. However, lacquer is not that far behind in terms of its durability.
If my time is limited, then lacquer offers definite advantages since the typical drying time for the product is just 30 minutes, give or take the humidity levels in the air. Shellac is not too far behind at one hour. And polyurethane that contains water will take about two hours to fully dry.
However, I avoid oil-based or standard versions of polyurethane as it can take upwards of 24 hours to fully dry.
Varnish is still the king as no other topcoat has its resistance to both UV rays and the elements.
If the topcoat has been scratched, dented, or otherwise marked, then lacquer is the easiest to fix. This is because applying a new coat of lacquer will actually help dissolve in part the older coat that is underneath. This means that imperfects are smoothed out when the new coat is applied.
Things to Keep in Mind
With all the advantages that the four major topcoats offer, it can be easy to lose track of which one is best for the particular woodworking project.
Tables vs. Flooring
There is a considerable difference between a table that I might sit a magazine or two on and a floor that I am walking on every day. Durability is the crucial factor when it comes to putting the right topcoat on the flooring. This means that I am less concerned about the effects of heat and more about foot traffic.
This can be of concern, especially if you have little ones or pets that live in the home. Polyurethane that has water included contains far fewer VOCs. Combined with a well-ventilated area and the danger is minimized.
Different topcoats cost different amounts of money. For smaller projects, the cost is not usually too much of a difference, although it is still noticeable. For larger projects, the cost can build up considerably when more cans have to be purchased.
CLosing thoughts: Finding the right topcoat takes a little research. But in the end, the four main topcoats offer clear advantages and disadvantages which make them easy to choose between them.
- Choosing the Right Topcoat