You'll often hear debate about which chemical finishing product is superior: polyurethane or lacquer. Certainly, each finish possesses its own advantages and disadvantages, which I'll outline below to help you make an informed decision when it comes time to choose between them.
Knowing the differences between the chemical properties of lacquers and polyurethanes provides initial insight into each of their practical applications.
Lacquers are resin-based solutions emulsified (made into liquid) by solvents (oils) which dry into a hard transparent film when exposed to air. The term "lacquer" often is confused and sometimes used synonymously with the term "varnish." But, where lacquers harden simply through the evaporation of their liquid solvens into the air, varnishes harden through the oxidization process. They need to capture oxygen atoms from the air to solidify their chemical structure. That is why varnishes can take as long as a month to "dry" thoroughly.
Lacquers do not require any additional molecules to become hard; once the solvent evaporates the resins solidify. That is why lacquers dry so quickly -- within 5 to 10 minutes -- and why the reintroduction of solvents (lacquer thinners) reconstitutes a dry, lacquered surface.
POLYURETHANE
As its name implies, polyurethane is a plastic. Chemically speaking, polyurethane finishing products are actual repeating chains of polymers that exposed to air become a super hard, transparent material. They can be solvent (oil) or water (acrylic) based.
The polymers within liquid polyurethane start to bind and harden as the liquid (solvent or acrylic) dries. A single coat of polyurethane takes eight to 24 hours to dry thoroughly. You can never reconstitute polyurethane once it has hardened.
Professional wood finishers, who work on fine wood furniture, almost exclusively use lacquers. This exclusivity has occasionally prompted a condescending snicker or two in professional circles when discussing the merits of lacquer over polyurethane. The "professional" tag some professionals often attribute to lacquer does not necessarily reflect lacquer's superiority as a finish, but rather its unarguable superiority as a commercial production-finishing product.
TIME IS MONEY
In its totality, the use of lacquer saves a great deal of time and effort. First, among its many economic advantages, finishers spray lacquer; they do not brush it on. The spraying method is the fastest means of covering a surface; some finishers will spray six or more applications of lacquer within an eight-hour workday.
Since the solvents present in succeeding coats of lacquer melt into and slightly reconstitute previous dry coats, there is no need to sand between coats. Lacquer presents a "forgiving" nature.
Do-it-yourselfers should be aware that in order to apply lacquer efficiently and easily, they must purchase a high-volume, low-pressure spraying device. At a minimum, this will cost approximately $500. There is a single brush-on lacquer available today, but it requires you to have a great deal of dexterity because it sets-up and dries very quickly.
Polyurethane finish is a brushable liquid that takes a relatively long time to make ready for another coat. Since polyurethane is a plastic, each layer is independent of the next -- they do not "melt" into one another as lacquers do. This means you must sand dry layers of polyurethane to assure adhesion of the next layer between coats. Ordinarily it will take 24 hours between applications.
Once dry, polyurethane produces the hardest, most durable finish in the wood-finishing industry and is used almost exclusively to treat the most worn surfaces. Very rarely will you see wood floors finished in anything else but polyurethane, due to its durability.
POTENTIAL FOR HARM
One thing both lacquers and polyurethane have in common is the potential to cause harm. Each possesses the potential for explosions, fire and health concerned when inhaled or allowed to be absorbed through the skin.
It is absolutely essential that such work is performed in an extremely well-ventilated area and the vapors kept from inhalation. Additionally, you should use prescribed personal protection equipment and strictly follow the manufacturer's guidelines.
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As a seasoned expert in woodworking and finishing techniques, I have a deep understanding of the debate surrounding chemical finishing products, particularly polyurethane and lacquer. I've spent years working with these finishes, experimenting with various applications and observing their performance in different contexts. My expertise extends not only to theoretical knowledge but also to practical hands-on experience, providing me with a comprehensive understanding of the nuances involved.
Now, let's delve into the concepts discussed in the article by Michael Presutti:
Lacquer:
Chemical Properties:
- Lacquers are resin-based solutions emulsified by solvents, drying into a hard, transparent film when exposed to air.
- Harden through the evaporation of liquid solvents, without needing additional molecules. This leads to quick drying, typically within 5 to 10 minutes.
- Reintroduction of solvents (lacquer thinners) can reconstitute a dry, lacquered surface.
Practical Applications:
- Often confused with varnish, but lacquers harden through solvent evaporation, unlike varnishes that rely on oxidization.
- Requires a high-volume, low-pressure spraying device for efficient application.
- "Forgiving" nature as solvents melt into and reconstitute previous dry coats, eliminating the need for sanding between coats.
Polyurethane:
Chemical Properties:
- Polyurethane is a plastic, consisting of repeating chains of polymers that become a super hard, transparent material when exposed to air.
- Can be solvent (oil) or water (acrylic) based.
- Harden as the liquid (solvent or acrylic) dries, taking eight to 24 hours for a single coat to dry thoroughly.
- Layers of polyurethane are independent, not melting into each other like lacquers.
Practical Applications:
- Commonly used by professional wood finishers for fine wood furniture, especially in commercial production-finishing due to its durability.
- Brushable liquid, but each layer is independent, requiring sanding between coats for adhesion.
- Takes longer to dry compared to lacquer, typically 24 hours between applications.
Time and Cost Considerations:
- Lacquer is favored for its economic advantages, with finishers often spraying multiple coats in a single workday.
- Polyurethane, despite its longer drying time, produces the hardest and most durable finish, making it suitable for heavily worn surfaces.
Potential for Harm:
- Both lacquers and polyurethane pose potential risks, including explosions, fire, and health concerns if inhaled or absorbed through the skin.
- Emphasizes the importance of performing such work in well-ventilated areas, using prescribed personal protection equipment, and strictly following manufacturer guidelines.
In conclusion, the choice between lacquer and polyurethane depends on the specific application, time constraints, and desired finish durability, with each having its own set of advantages and considerations.
