When it comes to woodworking and furniture finishing, the choice of finish can significantly affect the final product. Two of the most popular finishes in the industry are Polyurethane and Spar Urethane.
Both are renowned for their protective qualities, but each has unique characteristics and uses. So, which one is the best for outdoor use? Let’s dive in and find out.
Polyurethane: An Overview
Polyurethane is a type of synthetic varnish used for finishing and sealing wood. It’s known for its durability, versatility, and the high level of protection it offers. Polyurethane comes in various sheens, from satin to glossy, and can be oil- or water-based.
One of the key benefits of Polyurethane is its hardness. When fully cured, Polyurethane forms a hard, protective layer over the wood, making it resistant to scratches and wear. This makes it an excellent choice for high-traffic areas or pieces of furniture that see a lot of use.
So, is Polyurethane harder than Spar Urethane? The answer is yes. Polyurethane tends to be harder and more resistant to scratches, making it a go-to choice for indoor furniture, floors, and other surfaces that need a durable finish.
But Polyurethane isn’t just about protection. It also enhances the natural beauty of the wood. It adds depth to the wood grain and can give the wood a warm, rich glow. However, it’s worth noting that Polyurethane tends to yellow over time, especially the oil-based variety.
This yellowing can add a warm tone to the wood, but it might not be desirable on light-colored woods or white paints.
Spar Urethane: An Overview
Spar Urethane, also known as Marine Varnish, is another popular choice for wood finishing. It’s specifically designed for wood exposed to harsh conditions, particularly outdoor use. This is because Spar Urethane has excellent water, heat, and sunlight resistance, making it a great choice for outdoor furniture, decks, and boats.
One of the key features of Spar Urethane is its flexibility. Unlike Polyurethane, which forms a hard, rigid finish, Spar Urethane remains flexible after dries. This flexibility allows it to expand and contract with the wood as it responds to changes in temperature and humidity, reducing the risk of cracking or peeling.
But does Spar Urethane turn yellow? Like Polyurethane, Spar Urethane can also turn yellow over time, especially when exposed to sunlight. However, this yellowing is often less noticeable with Spar Urethane and can even be desirable in some cases, as it can add a warm, golden tone to the wood.
Another important question is, is Spar Urethane waterproof? The answer is yes. Spar Urethane is highly resistant to water, making it an excellent choice for outdoor use or for pieces that may come into contact with water.
Polyurethane vs Spar Urethane: A Direct Comparison
When choosing between Polyurethane and Spar Urethane, it’s essential to understand their differences and similarities. Both are excellent choices for wood finishing, but their unique properties make them better suited for different applications.
Properties
Polyurethane is known for its hardness and durability. It forms a hard, protective layer that is highly resistant to scratches and wear. This makes it an excellent choice for surfaces that require much use, such as floors and furniture.
On the other hand, Spar Urethane is known for its flexibility and water resistance. It remains flexible after drying, allowing it to expand and contract with the wood in response to changes in temperature and humidity.
This makes it less likely to crack or peel, making it an excellent choice for outdoor furniture and other wood exposed to the elements.
Uses
Polyurethane, including furniture, floors, and cabinets, is commonly used for indoor applications. Its hardness and wear resistance make it a great choice for high-traffic areas.
With its superior water and weather resistance, Spar Urethane is the go-to choice for outdoor applications. It’s commonly used on outdoor furniture, decks, boats, and other wood exposed to harsh conditions.
Benefits
Both Polyurethane and Spar Urethane offer excellent protection for wood. Polyurethane enhances the wood’s natural beauty, adding depth to the grain and a warm glow to the finish. It’s also easy to clean and maintain.
With its flexibility and water resistance, Spar Urethane offers superior protection for wood exposed to harsh conditions. It also has excellent UV resistance, helping to prevent the wood from graying and deteriorating under the sun.
Is Polyurethane Better Than Spar Urethane?
The answer to this question depends on your specific needs. If you’re working on an indoor project that requires a hard, durable finish, Polyurethane is likely the better choice. However, if you’re working on an outdoor project that needs a flexible, water-resistant finish, Spar Urethane would be the way to go.
Polyurethane: Pros and Cons
Like any other finish, Polyurethane has its advantages and disadvantages. Understanding these can help you decide if it’s the right choice for your project.
Pros of Polyurethane
- Durability: Polyurethane is known for its hardness and durability. It forms a hard, protective layer that is highly resistant to scratches and wear, making it an excellent choice for high-traffic areas.
- Versatility: Polyurethane comes in various sheens, from satin to glossy, and can be either oil-based or water-based. This versatility allows you to choose the right finish for your project.
- Enhances Wood’s Beauty: Polyurethane enhances the natural beauty of the wood. It adds depth to the wood grain and can give the wood a warm, rich glow.
- Easy to Clean and Maintain: Polyurethane is easy to clean and maintain. It’s resistant to most household cleaners, and minor scratches can be easily repaired.
Cons of Polyurethane
- Can Yellow Over Time: Polyurethane, especially the oil-based variety, can yellow over time. This yellowing can add a warm tone to the wood, but it might not be desirable on light-colored woods or white paints.
- Not Ideal for Outdoor Use: While Polyurethane is durable, it’s not the best choice for outdoor use. It lacks the flexibility of Spar Urethane, making it more susceptible to cracking and peeling in fluctuating temperatures and humidity.
- Application Can Be Tricky: Applying Polyurethane can be tricky. It tends to bubble during application, and these bubbles can harden into the finish if not properly addressed.
Spar Urethane: Pros and Cons
Spar Urethane also has its pros and cons. Let’s take a look at them.
Pros of Spar Urethane
- Excellent for Outdoor Use: Spar Urethane is designed for wood exposed to harsh conditions. It’s highly resistant to water, heat, and sunlight, making it a great choice for outdoor furniture, decks, and boats.
- Flexibility: Unlike Polyurethane, Spar Urethane remains flexible after it dries. This flexibility allows it to expand and contract with the wood as it responds to changes in temperature and humidity, reducing the risk of cracking or peeling.
- UV Resistance: Spar Urethane has excellent UV resistance. It helps prevent the wood from graying and deteriorating under the sun.
Cons of Spar Urethane
- Can Yellow Over Time: Similar to Polyurethane, Spar Urethane can also yellow over time, especially when exposed to sunlight. However, this yellowing is often less noticeable with Spar Urethane.
- Not as Hard as Polyurethane: Spar Urethane is not as hard as Polyurethane. While its flexibility is a benefit for outdoor use, it may not provide the same level of scratch resistance as Polyurethane for indoor applications.
- Longer Drying Time: Spar Urethane generally takes longer to dry than Polyurethane. This longer drying time can slow down your project and requires more care to prevent dust and bugs from sticking to the finish.
Choosing the Right Urethane for Your Project
Choosing between Polyurethane and Spar Urethane depends largely on the specifics of your project. Here’s a simple guide to help you make the right choice:
- Consider the Location: If your project is indoors and requires a hard, durable finish, Polyurethane is likely the better choice. However, if your project is outdoors and needs a flexible, water-resistant finish, Spar Urethane would be the way to go.
- Think About the Look You Want: Polyurethane tends to add a warm, rich glow to the wood, but it can yellow over time. If you’re working with light-colored woods or white paints, a water-based Polyurethane or Spar Urethane might be a better choice as they yellow less over time.
- Evaluate the Use: If your project involves a surface that will see a lot of wear and tear, such as a floor or a kitchen table, Polyurethane’s hardness and durability make it a good choice. For projects like outdoor furniture or a tabletop that needs to withstand the elements, the water and UV resistance of Spar Urethane make it a suitable option.
Safety Tips When Using Urethane
Working with urethane finishes requires certain safety precautions. Here are some tips to keep in mind:
- Ventilation is Key: Urethane finishes can release fumes that are harmful if inhaled. Always work in a well-ventilated area, and consider using a respirator if the area is not adequately ventilated.
- Protect Your Skin: Urethane can cause skin irritation. Wear gloves to protect your skin, and if you do get some on your skin, wash it off immediately with soap and water.
- Avoid Fire Hazards: Urethane finishes are flammable. Keep them away from open flames, and don’t smoke while applying them. Also, be aware that rags soaked in urethane can spontaneously combust if not properly disposed of. Always soak used rags in water before disposing of them in a sealed metal container.
- Store Safely: Keep urethane finishes out of the reach of children and pets. Store them in a cool, dry place away from heat sources.
How to Apply Spar Urethane
Applying Spar Urethane properly can enhance the longevity and appearance of your outdoor wood projects. Here’s a step-by-step guide on how to do it:
- Prepare the Surface: Start by sanding the wood surface to remove any old finish or rough spots. Use a tack cloth to remove any dust.
- Stir the Urethane: Stir the Spar Urethane gently to mix it. Avoid shaking the can as this can create bubbles.
- Apply the First Coat: Using a high-quality brush, apply the first coat of Spar Urethane. Always brush in the direction of the wood grain and avoid over-brushing, which can create bubbles.
- Let it Dry: Allow the first coat to dry completely. This can take several hours, depending on the temperature and humidity.
- Sand Between Coats: Once the first coat is dry, lightly sand the surface with fine-grit sandpaper. This helps the next coat adhere better. Wipe away the dust with a tack cloth.
- Apply Additional Coats: Repeat the process for at least two more coats. Remember to let each coat dry completely and to sand between coats.
- Let it Cure: After the final coat, let the finish cure for several days before using the piece.
FAQs about Polyurethane and Spar Urethane
Regarding Polyurethane and Spar Urethane, several questions often come up. Here are answers to some of the most frequently asked questions:
Can you apply Spar Urethane over Polyurethane?
Yes, you can apply Spar Urethane over Polyurethane. However, you’ll need to lightly sand the Polyurethane finish first to ensure the Spar Urethane adheres properly. Remember to clean off any dust before applying the Spar Urethane.
Is Spar Urethane harder than Polyurethane?
No, Polyurethane is generally harder than Spar Urethane. This makes Polyurethane more resistant to scratches and wear, making it a good choice for high-traffic areas or pieces of furniture that see a lot of use.
Does Spar Urethane turn yellow?
Yes, like Polyurethane, Spar Urethane can also yellow over time, especially when exposed to sunlight. However, this yellowing is often less noticeable with Spar Urethane.
Is Spar Urethane waterproof?
Yes, Spar Urethane is highly resistant to water, making it an excellent choice for outdoor use or for pieces that may come into contact with water.
Which is better for outdoor use, Polyurethane or Spar Urethane?
For outdoor use, Spar Urethane is generally the better choice. Its flexibility and resistance to water, heat, and sunlight make it more suitable for outdoor conditions.
The Science Behind Polyurethane
Polyurethane is a type of polymer, a large molecule composed of repeating structural units. These polymers are created through a chemical reaction known as polymerization, where multiple small molecules, called monomers, combine to form a larger, more complex structure.
In the case of Polyurethane, the reaction occurs between a diisocyanate and a polyol. The diisocyanate contains two isocyanate groups (-NCO), and the polyol contains multiple hydroxyl groups (-OH). When these two components react, they form a urethane linkage, characterized by the structure -NH-CO-O-. It’s this urethane linkage that gives Polyurethane its unique properties.
One of the key features of Polyurethane is its versatility. By varying the types of diisocyanates and polyols used, manufacturers can create Polyurethane with a wide range of properties, from soft and flexible to hard and rigid. This versatility makes Polyurethane suitable for various applications, from foam mattresses to protective wood finishes.
The Science Behind Spar Urethane
Spar Urethane, also known as Marine Varnish, is a type of varnish formulated to be flexible and resistant to harsh conditions such as sunlight, water, and temperature changes. The “spar” in Spar Urethane comes from its use in the marine industry, which was used to protect wooden spars on ships.
The flexibility of Spar Urethane comes from its chemical structure. Like Polyurethane, Spar Urethane is a polymer, but it’s formulated to have longer, more flexible chains of molecules. This flexibility allows the finish to expand and contract with the wood as it responds to changes in temperature and humidity, reducing the risk of cracking or peeling.
Spar Urethane also contains added UV blockers that help protect the wood from the damaging effects of the sun. These UV blockers absorb and dissipate the harmful UV radiation as heat, preventing the wood from graying and deteriorating under the sun.
The Future of Urethane
The field of urethane is constantly evolving, with new developments and trends emerging regularly. One of the key trends is the increasing focus on sustainability and environmental friendliness. This has led to the development of water-based Polyurethane and Spar Urethane, which have lower VOC (Volatile Organic Compounds) emissions and are less environmentally harmful.
Water-based Spar Urethane, in particular, is gaining popularity for its environmental benefits and excellent performance. It provides the same flexibility, water resistance, and UV protection as traditional Spar Urethane, but with less odor and a faster drying time. As more people become aware of the need for environmentally friendly products, the demand for water-based Spar Urethane will likely increase.
Another trend is the development of urethane with enhanced properties, such as improved scratch resistance, UV resistance, and durability. Technology and materials science advances enable the creation of urethane finishes that perform better and last longer, even in harsh conditions.
In the future, we can expect to see even more innovations in urethane. These could include new formulations with improved properties, more environmentally friendly options, and perhaps even smart finishes that can adapt to their environment.
Conclusion
Polyurethane and Spar Urethane are excellent choices for wood finishes, each with unique properties and uses. Polyurethane, with its hardness and durability, is ideal for indoor applications, while Spar Urethane, with its flexibility and weather resistance, is perfect for outdoor use.
Choosing between the two depends on your specific needs and the nature of your project. By understanding the properties, uses, and benefits and how to apply them properly, you can make an informed decision and achieve a beautiful, durable finish for your wood project.
The field of urethane is constantly evolving, with new developments and trends emerging regularly. As we look to the future, we expect to see even more innovations that will further enhance the performance and sustainability of urethane finishes.
