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Polyurethane and shellac are two of the most commonly used finishes in the world of woodworking and home improvement. While both are used to provide protection and enhance the appearance of wood surfaces, they have several differences that make them more suited for different applications. But, polyurethane vs shellac; what are the differences? When is it better to use one over the other?
Shellac is a natural product made from the resin of certain trees. It has been used as a wood finish for centuries. Shellac is durable and provides a high gloss finish. On the other hand, polyurethane is a synthetic product made from petroleum products. It was developed in the 20th century as an alternative to shellac. Polyurethane is more durable than shellac and provides a high gloss finish.
What Is Shellac?
Shellac is a resin that is secreted by the female lac bug. It has been used as a protective coating and sealant for centuries and was once the primary finish used in the furniture industry. It dries quickly, provides a hard and clear finish, and is easy to apply. Shellac is still a popular choice for antiques and fine woodwork, as it provides a natural look and enhances the beauty of the wood grain.
Properties Of Shellac
Durability: Despite its natural composition, shellac is a durable finish that can withstand wear and tear, making it a great choice for high-use items like tabletops, desks, and cabinetry.
Water Resistance: While shellac provides some level of water resistance, it is not waterproof, and prolonged exposure to water can cause it to soften or discolor.
Heat Resistance: Shellac has a relatively low melting point, making it susceptible to damage from heat.
UV Resistance: Shellac does not provide much protection from UV rays, which can cause it to yellow and become brittle over time.
Breathability: One of the unique properties of shellac is its breathability, which allows the wood to expand and contract with changes in temperature and humidity, helping to prevent cracking and splitting.
Ease of Application: Shellac is easy to apply with a brush, making it a great choice for DIY projects.
What Is Polyurethane?
Polyurethane is a synthetic resin that is commonly used as a clear protective coating for wood surfaces. It dries to a hard, crystal-clear finish that provides excellent protection against wear, tear, and moisture. Polyurethane is available in both oil-based and water-based formulas, and can be used for a wide range of applications, from furniture and cabinetry to flooring and trim.
Polyurethane is made up of two components: a polyol, which is alcohol with more than two hydroxyl groups, and an isocyanate, which is a compound containing the -NCO group. When the two are mixed, they react to form urethane links (–NHCOCH) between the polyol and isocyanate groups. These urethane links create a very tough, cross-linked polymer that is resistant to solvents and heat.
Properties of Polyurethane
Durability: Polyurethane is a highly durable finish that can withstand heavy use and exposure to moisture, making it a great choice for high-traffic areas like kitchen and bathroom floors, as well as for outdoor furniture and decks.
Water Resistance: Polyurethane provides excellent water resistance, making it a great choice for areas that are frequently exposed to moisture, such as kitchens, bathrooms, and outdoor spaces.
Chemical Resistance: Polyurethane is also resistant to chemicals and solvents, making it a great choice for areas that are exposed to spills or splashes, such as countertops and table tops.
UV Resistance: Polyurethane provides excellent protection from UV rays, making it a great choice for outdoor furniture and trim that is exposed to sunlight.
Flexibility: Polyurethane is a flexible finish that can accommodate changes in temperature and humidity, helping to prevent cracking and splitting.
Ease of Sanding: Polyurethane can be sanded to a smooth finish, making it easy to achieve a professional-looking result.
Polyurethane Vs Shellac; Similarities
Both Are Used as Protective Coatings: Both polyurethane and shellac are commonly used as protective coatings for wood surfaces. They provide a durable and long-lasting finish that helps to protect the wood from scratches, water damage, and other types of wear and tear.
Both Can Be Used on a Variety of Surfaces: Both polyurethane and shellac can be applied to a variety of surfaces, including wood, metal, and plastic. This versatility makes them ideal for a range of different projects, from furniture refinishing to DIY home improvements.
Both Offer a High-Gloss Finish: Both polyurethane and shellac are known for their high-gloss finish that provides a sleek and polished look. This makes them ideal for use on high-traffic surfaces or for creating a shiny and eye-catching finish.
Both Have a Quick Drying Time: Both polyurethane and shellac have a relatively quick drying time compared to other types of wood finishes. This makes them convenient to use and helps to reduce the amount of time required to complete a project.
Both Can Be Easily Sanded and Re-Coated: Both polyurethane and shellac can be easily sanded and re-coated if needed. This makes it easy to touch up the finish or to change the look of the surface over time.
Both Provide Good Protection Against Water: Both polyurethane and shellac provide good protection against water, which makes them ideal for use in areas that are prone to moisture or humidity. Whether you’re refinishing a kitchen table or protecting a bathroom vanity, both of these finishes will provide the protection you need to keep your surfaces looking great for years to come.
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Polyurethane Vs Shellac; Differences
Composition: One of the key differences between polyurethane and shellac is their composition. Polyurethane is a type of plastic made from the reaction of a polyol and an isocyanate, while shellac is a resin produced by the female lac bug.
Drying Time: Another key difference between the two is their drying time. Polyurethane takes longer to dry than shellac, often taking several hours to fully cure. On the other hand, shellac dries quickly, typically within 15-30 minutes.
Appearance: The appearance of the finished product can also differ between polyurethane and shellac. Polyurethane provides a clear, glossy finish, while shellac can have a slight amber tint and a matte finish.
Water Resistance: In terms of water resistance, polyurethane has a distinct advantage over shellac. Polyurethane provides excellent protection against water and moisture, while shellac is not as effective in this regard.
Durability: While both polyurethane and shellac are durable, polyurethane is considered to be more durable and scratch-resistant. Shellac, on the other hand, is more delicate and can be damaged by solvents or other chemicals.
Solvent Resistance: Finally, solvent resistance is another key difference between the two. Polyurethane is highly resistant to solvents and chemicals, while shellac can be dissolved or damaged by many common solvents.
When to Use Each:
When to Use Polyurethane: Polyurethane is ideal for use on surfaces that will be exposed to moisture or heavy wear and tear. It is also well-suited for use on surfaces that will be exposed to harsh chemicals or solvents.
When to Use Shellac: On the other hand, shellac is best suited for use on delicate or intricate surfaces that require a clear, non-yellowing finish. It is also ideal for use as a sealer or primer, as it dries quickly and can provide a smooth base for other finishes.
Preparation Before Applying Shellac or Polyurethane
Proper preparation is key to achieving a successful and long-lasting finish when using either shellac or polyurethane. Before you begin, make sure that the surface you’ll be working on is clean, dry, and free of any dust, dirt, or debris. If the surface has any cracks, dents, or imperfections, you should fill them in with wood filler and sand the surface smooth. You should also remove any old paint or finish from the surface and sand it lightly to help the new finish adhere properly.
It’s also important to consider the temperature and humidity in the room you’ll be working in. Both shellac and polyurethane have specific temperature and humidity requirements for proper application, and failure to meet these requirements can result in a poor-quality finish. It’s best to apply these finishes in a room that is between 60- and 80-degrees Fahrenheit, with a relative humidity of between 40% and 60%. If the temperature and humidity are too high, the finish will dry too quickly, resulting in a rough surface and poor adhesion. If the temperature and humidity are too low, the finish will dry too slowly and may not dry evenly.
In addition to these preparation steps, it’s important to choose the right tools for the job. For shellac, you’ll need a clean, soft-bristled brush for application, and for polyurethane, you can use either a brush or a roller. It’s important to use high-quality brushes and rollers, as lower-quality tools can leave streaks and bristles in the finish. Before you begin, make sure that your tools are clean and free of any debris that could affect the quality of the finish. With proper preparation and the right tools, you can ensure a successful and long-lasting finish with either shellac or polyurethane.
FAQs
What is the difference between polyurethane and shellac?
Polyurethane is a type of plastic made from the reaction of a polyol and an isocyanate, while shellac is a resin produced by the female lac bug.
Can polyurethane be applied over shellac?
Yes, polyurethane can be applied over shellac, as long as the shellac is fully cured and sanded smooth.
Is shellac the same as polyurethane?
No, shellac and polyurethane are not the same. They have different compositions, drying times, appearances, water resistance, durability, and solvent resistance.
Should I use shellac or polyurethane?
The choice between shellac and polyurethane will depend on the specific needs of your project. Consider the surface you are working with, the intended use of the surface, and any specific requirements such as water resistance or durability.
Is polyurethane more durable than shellac?
Polyurethane is considered to be more durable than shellac. Polyurethane is a type of plastic that is known for its strength and durability, while shellac is a resin secreted by the lac beetle that is used as a wood finish. Polyurethane is often used in high-traffic areas and on surfaces that are subjected to frequent wear and tear, while shellac is often used in low-traffic areas or as a sealer for other finishes. In terms of durability, polyurethane is more resistant to scratches, dings, and other forms of damage than shellac, making it a better choice for items that will be subjected to a lot of wear and tear.
Conclusion
When deciding between shellac and polyurethane, it is important to consider the specific use case. If you are looking for a natural finish for a low-traffic item, shellac is a great choice. However, if you are looking for a protective finish for a high-traffic item, polyurethane is the better option. Additionally, if you are looking for a finish that is water-resistant or heat-resistant, polyurethane is the better choice. Ultimately, the choice between shellac and polyurethane will depend on your specific needs and preferences.
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