Imagine walking into a room and immediately drawing your eyes to a stunning piece of wooden furniture. The grain, the color, the way the light bounces off the surface – it’s all part of the magic that a good wood finish can create. Wood finishes are the unsung heroes of the woodworking and home improvement world. They protect our beloved wooden pieces from damage, enhance their natural beauty, and breathe life into our homes.
Wood Finishes: Shellac and Polyurethane
Let’s dive into wood finishes, specifically shellac and polyurethane. These two are among the most popular choices for woodworkers and DIY enthusiasts. But what exactly are they? Where do they come from? And most importantly, what can they do for your wood?
Shellac
Shellac is a natural finish that has been used for centuries. It’s derived from the secretions of the lac bug, a tiny insect found in the forests of India and Thailand. The bugs consume tree sap and excrete “lac,” a sticky substance processed into shellac flakes. These flakes are then dissolved in alcohol to create the shellac finish we use today.
Shellac has a warm, amber hue that can bring out the character of the wood. It dries quickly, is easy to repair, and is even food-safe, making it a favorite for kitchen utensils and toys. However, it’s not as durable as some other finishes and can be damaged by heat and alcohol.
Polyurethane
On the other side of the spectrum, we have polyurethane, a synthetic finish introduced in the mid-20th century. Polyurethane is a type of varnish that forms a tough, plastic-like coating on the surface of the wood. It’s available in oil- and water-based forms, each with its advantages.
Polyurethane is known for its durability. It’s resistant to water, heat, and many household chemicals, making it a great choice for furniture, floors, and outdoor projects. It also comes in a range of sheens, from matte to high gloss, so you can choose the look that best suits your style. However, it takes longer to dry than shellac and can be more challenging to apply.
The Composition of Shellac and Polyurethane
Shellac
As we delve deeper into the world of wood finishes, it’s essential to understand what makes each unique. Shellac, as we’ve mentioned, is a natural product. It’s a resin secreted by the female lac bug (Laccifer lacca) found in the forests of India and Thailand. This resin is harvested and processed into dry flakes which, when dissolved in alcohol, form the shellac solution used as a wood finish. This natural origin gives shellac its unique characteristics, including its warm amber color and quick-drying properties.
Polyurethane
In contrast, polyurethane is a synthetic product. It’s a type of polymer—large molecules of repeating subunits—created through a chemical reaction involving polyol and isocyanate. The result is a durable, flexible finish that forms a hard, protective layer on the surface of the wood. Polyurethane’s synthetic nature allows it to resist many things that can damage wood, such as water, heat, and household chemicals.
Application Process: Shellac vs Polyurethane
Applying Shellac
The application process for shellac and polyurethane differs, reflecting their unique properties. For shellac, the first step is to ensure the wood surface is clean and smooth. Any dust or dirt can interfere with the finish, so thoroughly cleaning is crucial.
Next, the shellac flakes are dissolved in alcohol to create a liquid solution. This solution is then applied to the wood using a brush or cloth. Shellac dries quickly, often within minutes, so it’s important to work swiftly to avoid lap marks. Once the first coat is dry, additional coats can be applied to achieve the desired level of finish. Between coats, a light sanding with fine-grit sandpaper helps ensure a smooth, even finish.
Cleanup after applying shellac is relatively easy. Brushes and cloths can be cleaned with denatured alcohol, and spills can be wiped with a damp cloth.
Applying Polyurethane
The process for applying polyurethane is a bit more involved. Like shellac, the wood surface must be clean and smooth before starting. However, polyurethane also requires a well-ventilated area due to its strong fumes.
Polyurethane can be applied with a brush, roller, or sprayer, depending on the type of polyurethane (oil-based or water-based) and the size of the project. Applying thin, even coats is important to avoid drips and runs. Unlike shellac, polyurethane takes longer to dry, often several hours between coats. Light sanding between coats ensures a smooth finish.
Cleanup after using polyurethane can be more challenging. Oil-based polyurethane requires mineral spirits or paint thinner for cleanup, while water-based polyurethane can be cleaned with soap and water.
Durability and Moisture Resistance
Shellac
When it comes to durability and moisture resistance, shellac and polyurethane each have their strengths and weaknesses. As a natural product, Shellac is not as durable as its synthetic counterpart. It’s more susceptible to scratches and isn’t the best choice for high-traffic areas like kitchen tables or floors.
In terms of moisture resistance, shellac has a moderate level of water resistance. It can handle the occasional water spill, but prolonged exposure to moisture can cause it to turn white or cloudy, a phenomenon known as “blushing.” Additionally, shellac is soluble in alcohol, so it’s not the best choice for a bar top or anywhere it might come into contact with alcoholic beverages.
Polyurethane
Polyurethane, on the other hand, is a powerhouse of durability. Its hard, plastic-like coating can withstand heavy use, making it an excellent choice for floors, countertops, and outdoor furniture. It’s resistant to scratches, heat, and many household chemicals.
When it comes to moisture resistance, polyurethane outshines shellac. It forms a waterproof barrier that protects the wood from water damage, making it a popular choice for bathroom and kitchen cabinets and outdoor projects. However, it’s worth noting that while polyurethane is water-resistant, it’s not entirely waterproof. Prolonged exposure to water can still cause damage, so wiping up spills promptly is important.
Curing Time: Shellac vs Polyurethane
Shellac
Curing time is another factor to consider when choosing a wood finish. Shellac dries incredibly fast. It can be dry to the touch within minutes of application and fully cured within a few hours. This quick curing time allows multiple coats to be applied daily, speeding up the project timeline.
Polyurethane
Polyurethane, however, takes a bit longer to cure. Depending on the type (oil-based or water-based) and the environmental conditions, polyurethane can take anywhere from a few hours to several days to fully cure. This longer curing time means that projects finished with polyurethane will take longer. However, the trade-off is a highly durable, water-resistant finish that can withstand heavy use.
Toxicity Levels of Shellac and Polyurethane
Shellac
In the realm of wood finishes, safety and toxicity are important considerations. As a natural product, Shellac is generally considered safe and non-toxic once cured. It’s even used in the food and pharmaceutical industries to coat pills and candies. However, the alcohol used to dissolve shellac flakes can be flammable and should be handled carefully.
Polyurethane
Polyurethane, on the other hand, is a synthetic product and comes with more safety concerns. Oil- and water-based polyurethanes contain volatile organic compounds (VOCs) that can be harmful if inhaled. These VOCs are released into the air during application and as the finish dries. Therefore, working in a well-ventilated area and using appropriate protective equipment, such as gloves and a respirator, is crucial.
Once fully cured, polyurethane is generally considered safe for normal use. However, it’s not food-safe, so it’s not the best choice for cutting boards or bowls.
Color Alteration: How Shellac and Polyurethane Affect Wood Color
Shellac
When it comes to aesthetics, both shellac and polyurethane can impact the color of the wood. With its warm amber hue, Shellac can enhance the natural color and grain of the wood, giving it a rich, warm glow. This can be a desirable effect, especially on woods with a beautiful grain pattern. However, it can also darken lighter woods or alter the color of stained wood.
Polyurethane
Polyurethane, on the other hand, is typically clear and does not significantly alter the color of the wood. It’s available in both gloss and satin finishes, allowing you to choose the level of shine that best suits your project. However, oil-based polyurethane can yellow over time, especially when exposed to sunlight. This can add a warm tone to the wood but also alter the color of light-colored woods or whites.
Cost Comparison: Shellac vs Polyurethane
Shellac
When budgeting for a woodworking project, the finish cost is an important factor to consider. Shellac is generally less expensive than polyurethane. It’s available in dry flakes that you dissolve in alcohol, allowing you to control the thickness of the solution and potentially get more coverage from a single package. However, keep in mind that the cost can vary depending on the quality and brand of the shellac.
Polyurethane
Polyurethane, on the other hand, tends to be more expensive. It’s a high-performance finish that offers superior durability and water resistance, and its price reflects these qualities. However, considering its long-lasting protection and the potential to reduce future maintenance costs, many woodworkers find polyurethane cost-effective in the long run.
Shelf Life and Storage of Shellac and Polyurethane
Shellac
Proper storage can extend the shelf life of both shellac and polyurethane. Shellac flakes have an almost indefinite shelf life if kept dry and away from heat. However, once mixed with alcohol, shellac has a shelf life of about 6 months to a year. After this time, it may not dry properly when applied. You can apply a small amount to a non-porous surface to test old shellac. If it dries in a reasonable time, it’s still good to use.
Polyurethane
Polyurethane, whether oil-based or water-based, has a longer shelf life—often several years if stored properly. It should be sealed in its original container and stored in a cool, dry place away from heat sources and freezing temperatures. If the polyurethane becomes thick or stringy, or if a skin forms on the surface, it’s no longer good to use.
Popular Products: Shellac and Polyurethane
Shellac
There are several popular shellac products on the market that woodworkers swear by. One such product is “It’s Knot Shellac,” a clear shellac solution ready to use straight out of the can. It’s known for its easy application and quick drying time, making it a favorite among DIY enthusiasts.
Polyurethane
In polyurethane, “CrystaLac Extreme Protection POLYURETHANE” is a standout product. This water-based polyurethane is praised for its durability and environmental friendliness. It provides a hard, clear finish resistant to water and household chemicals, making it an excellent choice for high-use furniture and floors.
Using Shellac and Polyurethane in Real Projects
Shellac
A real-world example of shellac in use can be seen in antique furniture restoration. One woodworker, for instance, used shellac to restore an early 20th-century oak table. The shellac brought out the wood’s natural grain and color, giving the piece a warm, rich glow. Plus, because shellac is easy to repair, any future damage to the table’s finish can be easily touched up.
Polyurethane
On the other hand, polyurethane is often the finish of choice for new furniture builds. For example, a custom-made dining table was finished with several coats of polyurethane to protect it from daily use. The polyurethane provided a durable, water-resistant finish that could withstand spills, heat from hot dishes, and the wear and tear of family meals. Plus, the clear finish allowed the beauty of the wood to shine through, enhancing the table’s aesthetic appeal.
FAQs
What is the difference between shellac and polyurethane?
Shellac is a natural finish derived from the secretions of the lac bug, while polyurethane is a synthetic finish that forms a durable coating on the wood’s surface.
Is shellac safe to use?
Once cured, shellac is generally considered safe and non-toxic. However, care should be taken when handling alcohol-dissolving shellac flakes.
Is polyurethane waterproof?
Polyurethane provides a waterproof barrier on the wood’s surface, making it resistant to water damage. However, prolonged exposure to water can still cause damage.
Which finish is more durable: shellac or polyurethane?
Polyurethane is generally more durable and can withstand heavy use and exposure to household chemicals better than shellac.
Can shellac be used on outdoor projects?
Shellac is not recommended for outdoor use as it is susceptible to moisture and UV exposure damage.
How long does it take for shellac and polyurethane to dry?
Shellac dries quickly, often within minutes, while polyurethane can take several hours to dry between coats.
Can I apply polyurethane over shellac?
Yes, you can apply polyurethane over shellac, but it’s important to ensure it is fully cured and lightly sanded before applying it.
Conclusion
Both shellac and polyurethane offer distinct qualities and benefits for wood finishes. Shellac is a natural product that enhances the wood’s natural beauty with its warm, amber hue. It dries quickly and is easy to repair. However, it is less durable and not as moisture-resistant as polyurethane.
Polyurethane, on the other hand, is a synthetic finish known for its durability and water resistance. It provides a hard, protective layer on the wood’s surface and can withstand heavy use. However, it takes longer to dry and may require more careful application.
When choosing between shellac and polyurethane, consider the specific needs of your project. If you’re looking for a natural, warm finish and don’t require extreme durability or moisture resistance, shellac can be a good choice. Polyurethane is the better option if durability, water resistance, and long-term protection are key factors.
