In the world of woodworking, the finish is the final touch, the grand finale that seals the deal. It’s the protective layer that also enhances the beauty of the wood. Two of the most popular finishes are polyurethane and lacquer. But what happens when you apply polyurethane over lacquer? Is it a match made in heaven or a recipe for disaster? This article will delve into the nitty-gritty of this topic, providing you with the knowledge you need to make informed decisions about your woodworking projects.
Understanding the Basics
Before we dive into the deep end, let’s get our feet wet with some basic concepts. Understanding the materials we work with is crucial to achieving the desired outcome. So, what are polyurethane, lacquer, varnish, Shellac, spar urethane, and water-based finishes? Let’s break it down.
Polyurethane
Polyurethane is a type of synthetic varnish used for finishing and sealing wood. It’s known for its durability and resistance to damage, including scratches, heat, and chemicals.
Polyurethane comes in two types: oil-based and water-based. The oil-based variety adds a warm, amber hue to the wood, while the water-based type is clear, making it a good choice for light-colored woods.
Lacquer
Lacquer is a clear or colored finish that dries by solvent evaporation. It’s often used on furniture, cabinets, and other woodwork. Lacquer provides a hard, durable finish that can be polished to a high gloss or rubbed to a satin or flat finish.
There are two types of lacquer: catalyzed and regular.
- Catalyzed lacquer is a premium finish, offering superior durability and resistance to water, acid, alkali, and chipping.
- Regular lacquer, on the other hand, is easier to work with but less durable.
Varnish, Shellac, and Spar Urethane
Varnish is a transparent, hard, protective finish or film primarily used in wood finishing. Shellac, a natural product made from a resin secreted by the female lac bug, is used as a primer, sanding sealant, tannin-blocker, odor-blocker, and high-gloss varnish. Spar urethane is a type of polyurethane often used on wood exposed to water, sunlight, and temperature changes, like outdoor furniture and boats.
Water-Based Finishes, Top Coat, and Clear Coat
Water-based finishes are clear and have low VOC (Volatile Organic Compounds) levels. They’re non-flammable and dry quickly. A top coat is the final layer of finish applied to a surface, providing protection and enhancing the appearance of the material beneath it. A clear coat is a transparent layer of paint applied over colored paint or finish.
Difference Between Polyurethane and Lacquer
When choosing a finish for your woodworking project, the decision often boils down to polyurethane versus lacquer. Both are popular choices but have distinct properties that make them suitable for different applications. Let’s compare and contrast these two finishes to help you make an informed decision.
Polyurethane
As we’ve already discussed, polyurethane is a synthetic varnish known for its durability and resistance. It’s a champion for protecting wood from scratches, heat, and chemicals. Polyurethane finishes are typically thicker, creating a hard, protective shell over the wood. This makes them an excellent choice for high-traffic areas or pieces that will be used, like floors or kitchen tables.
Polyurethane comes in both oil-based and water-based varieties. Oil-based polyurethane adds a warm, amber hue to the wood and is more durable but takes longer to dry. On the other hand, water-based polyurethane is clear and dries quickly, but it’s not quite as tough as its oil-based counterpart.
Lacquer
Lacquer is a clear or colored wood finish that dries by solvent evaporation. It’s known for its smooth, lustrous finish that enhances the natural beauty of the wood. Lacquer finishes are thinner and penetrate deeper into the wood, providing protection while preserving the wood’s texture and grain.
Lacquer dries incredibly fast, which can be a blessing or a curse depending on your project. On the one hand, it allows for quick recoating. On the other hand, it requires a skilled hand to apply evenly before it dries.
There are two types of lacquer: catalyzed and regular. Catalyzed lacquer is more durable and resistant to damage but is also more challenging to work with. Regular lacquer is less durable but easier to apply and repair.
Can I Put Polyurethane on Top of Lacquer?
The question of whether you can apply polyurethane over lacquer is one that often pops up in woodworking circles. The answer, however, isn’t as straightforward as a simple yes or no. It’s more of a “it depends.”
Polyurethane and lacquer are both finishes but have different properties and are not always compatible. Polyurethane is a more durable and flexible finish, while lacquer is more brittle. If you apply a polyurethane finish over a lacquer finish, the more flexible polyurethane might cause the lacquer underneath to crack.
However, it’s not impossible to apply polyurethane over lacquer, but it requires careful preparation. The lacquer must be fully cured, which can take several weeks. Then, the lacquered surface needs to be cleaned and lightly sanded to provide a “tooth” for the polyurethane to adhere to. Even with these steps, there’s still a risk of the lacquer cracking under the polyurethane, so it’s a method best left to experienced woodworkers.
Preparation for Applying Polyurethane Over Lacquer
Before applying polyurethane over lacquer, surface preparation is paramount. This process ensures that the polyurethane adheres properly to the lacquer, resulting in a smooth and durable finish. Here are the steps for preparing the lacquer surface for polyurethane application:
Ensure the lacquer is fully cured: Lacquer must be cured before applying polyurethane over it. This process can take several weeks.
Sand the surface: Lightly sand the lacquered surface using 100-grit sandpaper. This step creates a bondable surface for the polyurethane.
Clean the surface: After sanding, remove all dust and debris from the surface using a tack cloth. This step ensures that the polyurethane can adhere properly to the lacquer.
Stir the polyurethane: Stir the polyurethane gently to mix it well. Avoid shaking the can as this can create air bubbles, leaving bumps on the surface when applied.
Step-by-Step Guide to Applying Polyurethane Over Lacquer
Applying polyurethane over lacquer can be a meticulous process, but with careful application, the result is a smooth and durable finish. Here’s a step-by-step guide:
Apply the first coat: Using a bristle brush, apply the first coat of polyurethane in long, broad strokes. Keep the application thin and even to prevent pooling or dripping.
Let it dry: Allow the first coat to dry completely. This process can take 24 hours for oil-based polyurethane and 4 to 6 hours for water-based polyurethane.
Sand the surface: Lightly sand the surface using 220-grit sandpaper once the first coat is dry. This step helps the next coat adhere better to the surface.
Apply the second coat: Apply the second coat of polyurethane just like the first one. Let it dry completely.
Repeat the process: If necessary, repeat the sanding and coating process until you achieve the desired finish.
Polyurethane Over Lacquer: Durability and Maintenance
Polyurethane over lacquer creates a durable finish that can withstand wear and tear. However, it’s not invincible and requires regular maintenance to keep it looking its best. Regular dusting and cleaning with a damp cloth can help maintain the finish. Avoid harsh chemicals or abrasive cleaners, as they can damage the finish.
Polyurethane Over Lacquer: Heat Resistance and Toxicity
Polyurethane is known for its excellent heat resistance, which makes it a popular choice for kitchen tables and other surfaces that might be exposed to heat. However, it’s important to remember that while polyurethane can withstand heat better than other finishes, it’s not heat-proof.
In terms of toxicity, polyurethane, and lacquer contain volatile organic compounds (VOCs) that can be harmful if inhaled. Always use these products in a well-ventilated area and consider wearing a mask to avoid inhaling the fumes. Water-based polyurethanes and lacquers generally contain fewer VOCs and have less odor than their oil-based counterparts.
Can I Use Lacquer and Polyurethane Together?
While applying polyurethane over lacquer can be tricky, there are scenarios where using both can be beneficial. For instance, you might use lacquer to achieve a smooth, glossy finish on your piece, then top it with polyurethane for added durability and protection.
Again, the key is proper preparation and application. The lacquer must be fully cured and prepared before applying the polyurethane. Also, remember that water-based polyurethane is less likely to cause problems when applied over lacquer than oil-based polyurethane.
Can You Put Lacquer Over Water-Based Polyurethane?
When applying lacquer over water-based polyurethane, the waters get a bit murky. As a rule of thumb, applying lacquer over any water- or oil-based polyurethane is generally not recommended. The primary reason is that lacquer contains strong solvents that can soften and dissolve polyurethane, leading to a compromised finish.
However, if you’re determined to use lacquer over water-based polyurethane, there are steps you can take to increase the chances of success. First, ensure the polyurethane finish is fully cured, which can take up to a month. Then, lightly sand the surface to create a mechanical bond for the lacquer. Use a high-quality, water-based lacquer to minimize the risk of the underlying polyurethane dissolving. Even with these precautions, it’s risky and not typically recommended for beginners.
Can You Put Varnish on Top of Lacquer?
The question of whether you can apply varnish over lacquer is another common one. Much like with polyurethane and lacquer, the answer is that it’s possible but not without its challenges.
Varnish, like polyurethane, is a more flexible finish than lacquer. This means that applying varnish over lacquer can lead to the lacquer cracking due to the movement of the varnish. Additionally, varnish requires a porous surface to adhere properly, something that lacquer, with its smooth, sealed surface, does not provide.
If you decide to apply varnish over lacquer, the lacquer must be fully cured, and the surface must be lightly sanded to create a bondable surface for the varnish. However, due to the potential for cracking and adhesion problems, it’s generally best to use either varnish or lacquer, not both.
Clear Coat Over Lacquer
Applying a clear coat over lacquer is a common practice in the woodworking world. The clear coat, as the name suggests, is a transparent layer of finish applied over the lacquer to provide additional protection and enhance the appearance of the wood.
The benefits of applying a clear coat over lacquer are numerous.
- It adds an extra layer of protection against scratches, wear, and damage from UV light.
- It also enhances the depth and luster of the lacquer finish, making the wood’s color and grain more vibrant.
To apply a clear coat over lacquer:
- first, ensure the lacquer is fully cured.
- Then, lightly sand the lacquered surface with fine-grit sandpaper to create a bondable surface for the clear coat.
- Apply the clear coat in thin, even layers, allowing each layer to dry fully before applying the next.
- Once the final layer is dry, you can buff the surface to your desired gloss level.
Is It Better to Use Lacquer or Polyurethane?
The question of whether it’s better to use lacquer or polyurethane is a bit like asking whether it’s better to use a hammer or a screwdriver. The answer depends on the task at hand.
Lacquer shines when it comes to achieving a smooth, lustrous finish quickly.
- It dries incredibly fast, allowing for quick recoating, and it enhances the natural beauty of the wood.
- However, it’s not as durable as polyurethane and can be more challenging to apply evenly.
Polyurethane, on the other hand, is the go-to finish for durability.
- It creates a hard, protective shell over the wood, making it an excellent choice for high-traffic areas or pieces that will be used.
- However, it takes longer to dry and can alter the wood’s color, especially in oil-based polyurethane.
Lacquer Over Polyurethane
Applying lacquer over polyurethane is not a common practice and is generally not recommended. As we’ve discussed earlier, lacquer contains strong solvents that can soften and dissolve polyurethane, leading to a compromised finish.
However, if you find yourself in a situation where you need to apply lacquer over polyurethane, there are steps you can take to increase your chances of success.
- The polyurethane finish must be fully cured, which can take up to a month.
- Then, the surface should be lightly sanded to create a bondable surface for the lacquer.
- Use a high-quality, water-based lacquer to minimize the risk of the underlying polyurethane dissolving.
Remember that this is a risky proposition and not typically recommended for beginners or pieces that will see heavy use or exposure to heat or chemicals.
Shellac Over Lacquer
Applying Shellac over lacquer is a more feasible proposition. A natural resin, Shellac is compatible with most other finishes, including lacquer. It’s often used as a sealant or barrier coat between incompatible finishes.
Applying Shellac over lacquer can provide additional protection and create a barrier that prevents the lacquer’s solvents from affecting subsequent layers of finish. It can also add a warm, amber tone to the piece, enhancing the wood’s natural color and grain.
To apply Shellac over lacquer:
- First, ensure the lacquer is fully cured.
- Then, lightly sand the surface to create a bondable surface for the Shellac.
- Apply the Shellac in thin, even coats, allowing each coat to dry fully before applying the next.
- Once the final coat is dry, you can apply your final finish, if desired.
Spar Urethane Over Lacquer
Applying spar urethane over lacquer is a technique that can be used to provide additional protection to outdoor furniture or other wood pieces exposed to the elements. Spar urethane is a polyurethane formulated to resist water, sunlight, and temperature changes, making it an excellent choice for outdoor applications.
However, as with applying any finish over lacquer, some important considerations must be remembered.
- The lacquer must be fully cured, which can take several weeks.
- The lacquered surface should be lightly sanded to create a bondable surface for the spar urethane.
- Apply the spar urethane in thin, even coats, allowing each coat to dry fully before applying the next.
The benefits of applying spar urethane over lacquer include enhanced durability and protection against the elements. However, it’s important to note that spar urethane will add a slight amber tint to the piece, which may alter the appearance of the lacquer finish.
Top Coat Over Lacquer
Applying a top coat over lacquer is a common practice in woodworking. A top coat is the final layer of finish applied to a surface, providing additional protection and enhancing the appearance of the material beneath it.
Applying a top coat over lacquer is similar to applying any other finish over lacquer.
- The lacquer must be fully cured, and the surface should be lightly sanded to create a bondable surface for the top coat.
- Apply the top coat in thin, even coats, allowing each coat to dry fully before applying the next.
Applying a top coat over lacquer includes added protection against wear and tear and an enhanced, polished appearance. Depending on the type of top coat used, it can also add depth and luster to the lacquer finish, making the wood’s color and grain more vibrant.
Water-Based Finish Over Lacquer
Applying a water-based finish over lacquer is a technique that can be used to provide a clear, protective layer over a lacquered piece. Water-based finishes are known for their low VOC levels, non-flammability, and quick drying times.
However, as with any finish applied over lacquer, there are some important steps to follow.
The lacquer must be fully cured, which can take several weeks.
- Then, the lacquered surface should be lightly sanded to create a bondable surface for the water-based finish.
- Apply the water-based finish in thin, even coats, allowing each coat to dry fully before applying the next.
The benefits of applying a water-based finish over lacquer include added protection against wear and tear, and a clear finish that doesn’t alter the color of the lacquer beneath it. However, water-based finishes are not as durable as oil-based finishes, so they may not be the best choice for high-traffic areas or pieces that will see heavy use.
Can You Stain Over Lacquer?
Staining over lacquer is not typically recommended. Lacquer creates a smooth, sealed surface that stain cannot penetrate. If you try to stain over lacquer, the stain will sit on the surface and wipe off, failing to change the color of the wood.
However, if you’re determined to change the color of a lacquered piece, there are some steps you can take. First, the lacquer must be fully cured. Then, the lacquered surface should be lightly sanded to create a bondable surface for the stain. Apply a gel stain, which is thicker and can sit on the surface of the wood, rather than a traditional liquid stain, which requires a porous surface to penetrate.
Remember that staining over lacquer is tricky and may not yield the desired results. It’s generally better to remove the lacquer, stain the wood, and then reapply it or another finish to seal the stain.
How to Test Whether You Have Catalyzed or Regular Lacquer
Identifying whether you have catalyzed or regular lacquer can be tricky, as they look similar. However, you can perform a few tests to help determine the type of lacquer you have.
One method is to test the lacquer’s resistance to certain chemicals. Catalyzed lacquer is more resistant to chemicals than regular lacquer. Try applying a small amount of acetone (found in nail polish remover) to a hidden area of the piece. If the finish softens or dissolves, it’s likely regular lacquer. If it remains unaffected, it’s probably catalyzed lacquer.
Another method is to look at the finish’s appearance and durability. Catalyzed lacquer tends to have a more durable, water-resistant finish than regular lacquer. If the finish shows signs of water damage or wear, it’s likely regular lacquer.
Remember, these tests are not foolproof, and it can be difficult to determine the type of lacquer with certainty. When in doubt, it’s best to consult a professional.
Conclusion
In woodworking and furniture finishing, understanding the intricacies of different finishes such as polyurethane, lacquer, stain, varnish, clear coat, top coat, and water-based finishes is crucial. Each finish has its unique properties, benefits, and challenges, and knowing how to use them individually or in combination can significantly impact the outcome of your project.
The world of wood finishes is vast and complex, but with some knowledge and practice, you can navigate it confidently. So, don’t be afraid to experiment, learn from your mistakes, and, most importantly, have fun. After all, every piece of wood has a story; as a woodworker, you get to be a part of that story.
