What Is the Difference Between Spar Varnish and Spar Urethane?




varnishing wood

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When it comes to protecting and enhancing the natural beauty of wood, nothing compares to the timeless appeal of a finely finished surface. For centuries, artisans and craftsmen have sought to preserve and elevate the aesthetics of their wooden creations using various coating techniques. Two such popular options are Spar Varnish and Spar Urethane, both known for their durability and resistance to harsh environmental elements. However, despite their shared reputation for wood protection, these two finishes possess distinct characteristics that cater to different needs and preferences.

Spar varnish and spar urethane are two popular wood finishes used for outdoor projects and marine applications. Understanding the differences between these two products is important when it comes to choosing the right finish for your project.

In this comprehensive guide, we aim to shed light on the fascinating differences between Spar Varnish and Spar Urethane. We will delve into the composition, application process, benefits, and ideal usage scenarios for each, empowering you with the knowledge to make informed decisions for your woodworking projects.

So, whether you are a seasoned woodworking enthusiast or a novice looking to embark on your first project, join us on this journey to explore the world of protective wood finishes and discover which one best suits your specific needs. Let’s dive into the nitty-gritty details of Spar Varnish and Spar Urethane to help you achieve the perfect finish that not only preserves your wood’s natural beauty but also stands the test of time against the elements.

What is Spar Varnish?

Spar varnish is a traditional wood finish that has been used for hundreds of years. It is made from a combination of natural resins, oils, and solvents. The ingredients are carefully selected to provide a durable, water-resistant finish that can withstand harsh weather conditions and UV rays.

Spar varnish is commonly used for outdoor furniture, decks, and boats. It provides a high-gloss finish that gives wood a warm, rich appearance. The natural ingredients used in spar varnish also help to protect the wood from drying out and cracking.

One of the key benefits of spar varnish is its ability to “breathe”. This means that the finish allows air and moisture to circulate freely, helping to prevent the wood from warping or splitting. However, this also means that spar varnish may need to be reapplied more frequently than other finishes, such as spar urethane.

How To Apply Spar Varnish?

Applying Spar Varnish is a straightforward process, but it requires some careful preparation and attention to detail to achieve the best results. Spar Varnish is specifically formulated to protect wood surfaces from exposure to moisture, sunlight, and other environmental elements, making it an ideal choice for outdoor projects such as boats, decks, and outdoor furniture. Here’s a step-by-step guide on how to apply Spar Varnish:

Materials You’ll Need:

  1. Spar Varnish (Oil-based or Water-based, depending on your preference)
  2. Fine-grit sandpaper (220-grit is recommended)
  3. Clean, lint-free cloths or brushes
  4. Tack cloth or microfiber cloth
  5. Paint stirrer or wooden stick
  6. Paint tray or container
  7. Paintbrush or foam brush (natural bristles for oil-based varnish and synthetic bristles for water-based varnish)
  8. Drop cloth or newspaper to protect the work area
  9. Optional: painter’s tape or masking tape (for precision application)

Step-by-Step Application Process:

1. Prepare the Surface

Ensure that the wood surface is clean, dry, and free of any dust, debris, or previous finishes. Sand the surface using fine-grit sandpaper to create a smooth and uniform texture. Sanding also helps the varnish adhere better to the wood.

2. Clean the Surface

Wipe down the sanded surface with a tack cloth or microfiber cloth to remove any lingering dust or particles. This step is crucial as any debris left on the surface can affect the final finish.

3. Stir the Varnish

If using an oil-based varnish, stir it gently with a paint stirrer or a wooden stick. Avoid shaking the can vigorously, as it can introduce bubbles into the varnish. For water-based varnish, shaking is fine, but stirring gently is also an option.

4. Apply the First Coat

Dip your paintbrush or foam brush into the Spar Varnish and apply a thin, even coat along the grain of the wood. Avoid over-brushing to prevent bubbles and uneven application. If using painter’s tape or masking tape, apply it to any areas you want to keep varnish-free.

5. Allow Drying Time

Let the first coat dry as per the manufacturer’s instructions. This usually takes several hours, depending on the temperature and humidity. Avoid any contact with the varnished surface during this time to prevent blemishes.

6. Sand Lightly (Optional)

If you desire an exceptionally smooth finish, you can lightly sand the dried first coat with fine-grit sandpaper. Remember to wipe off the sanding dust before proceeding.

7. Apply Additional Coats

Apply two or more additional coats of Spar Varnish, allowing each coat to dry between applications. The number of coats depends on the level of protection and sheen you desire. Sand lightly between coats if desired.

8. Final Drying and Curing

After the final coat, let the varnish dry and cure completely as per the manufacturer’s instructions. This final curing process ensures the varnish achieves its maximum hardness and durability.

9. Enjoy Your Finished Project

Once the Spar Varnish has fully cured, your wood project is ready to face the elements while maintaining its natural beauty. Enjoy the stunning results and the knowledge that your creation is now protected for years to come.

Remember to follow the manufacturer’s instructions on the product label for specific guidelines related to application, drying times, and clean-up. With proper application, Spar Varnish can provide a beautiful and durable finish to your outdoor wood projects.

What is Spar Urethane?

Spar urethane is a modern wood finish that is made from synthetic resins and solvents. Unlike spar varnish,

it provides a much more durable and long-lasting finish, thanks to its high resistance to UV rays, water, and other environmental elements.

Spar urethane is commonly used for marine applications, as well as for outdoor furniture and decks. Unlike spar varnish, it provides a low-gloss finish that can range from satin to semi-gloss, giving wood a more natural appearance.

One of the key benefits of spar urethane is its long-lasting protection. This finish can last for several years without cracking, peeling, or fading, making it a popular choice for outdoor projects.

How To Apply Spar Urethane?

Applying spar urethane is a straightforward process, but it requires attention to detail and careful execution to achieve the best results. Spar urethane is a durable and weather-resistant finish commonly used on outdoor wood surfaces such as decks, fences, and furniture. Here’s a step-by-step guide on how to apply spar urethane:

Materials and Tools Needed:

  1. Spar urethane (oil-based or water-based, depending on your preference)
  2. Stir stick
  3. Clean, lint-free cloths or brushes
  4. Sandpaper (220-grit or higher)
  5. Drop cloths or plastic sheets
  6. Safety goggles and gloves
  7. Well-ventilated work area

Step-by-Step Application Process:

1. Prepare the Surface

Ensure the wood surface is clean, dry, and free from any dust, debris, or old finish. If necessary, sand the wood with fine-grit sandpaper to create a smooth surface for better adhesion. Wipe away any sanding residue with a clean cloth.

2. Stir the Spar Urethane

Open the spar urethane can and use a stir stick to gently stir the contents. Avoid vigorous shaking, as it can introduce air bubbles into the finish, leading to an uneven application.

3. Test in a Small Area

If you’re using spar urethane for the first time or if you are uncertain about the compatibility with your wood surface, perform a test application in a small inconspicuous area. This will help you check the color and how the finish interacts with the wood.

4. Application

You can apply spar urethane using a brush, cloth, or foam applicator. Each method has its advantages, so choose one that suits your project and comfort.

  • Brush Application: Dip a high-quality natural bristle brush into the spar urethane, then remove any excess on the rim of the can. Apply a thin, even coat following the wood’s grain. Avoid over-brushing to prevent brush marks and bubbles. Allow the first coat to dry as per the manufacturer’s instructions.
  • Cloth Application: Dip a clean, lint-free cloth into the spar urethane, saturating it slightly. Wipe the finish onto the wood, again following the grain. This method is useful for smaller areas or intricate woodwork. Allow the first coat to dry.
  • Foam Applicator: Foam brushes or foam applicators can be useful for smooth surfaces, as they minimize brush marks. Apply in the same manner as with a brush or cloth.

5. Drying and Sanding Between Coats

Follow the manufacturer’s instructions for drying time between coats. Typically, you’ll need to wait several hours to let the first coat dry completely. Once dry, lightly sand the surface with a fine-grit sandpaper (220-grit or higher). This helps to create a smooth surface and promotes adhesion for subsequent coats. Wipe away any sanding dust with a clean cloth.

6. Apply Additional Coats

For optimal protection and a beautiful finish, apply two or more coats of spar urethane, following the same application method as before. Sand lightly between each coat to ensure a smooth surface.

7. Final Drying Time

After applying the final coat, let the spar urethane cure for the recommended drying time. Avoid exposing the finished surface to heavy use or moisture until it has thoroughly cured.

Remember, proper ventilation and safety precautions are essential when working with any finish. Spar urethane emits fumes, so work in a well-ventilated area, wear safety goggles and gloves, and follow the manufacturer’s safety guidelines.

Differences Between Spar Varnish and Spar Urethane

Spar Varnish Vs Spar Urethane

While both spar varnish and spar urethane provide a protective finish for outdoor wood, there are several key differences between these two products.

Let’s delve into their characteristics:

1. Composition

  • Spar Varnish: Spar varnish is typically oil-based and contains natural resins like linseed or tung oil, combined with a resin like alkyd. It also incorporates UV absorbers and inhibitors to protect the wood from the sun’s harmful rays.
  • Spar Urethane: Spar urethane, on the other hand, is a synthetic product, a type of polyurethane specifically formulated for outdoor use. It often combines urethane resin with other chemicals to enhance durability and UV resistance.

2. Durability

When it comes to durability, spar urethane is the clear winner. This synthetic finish provides much better protection against UV rays, water, and other environmental elements, making it a more suitable choice for marine and outdoor applications.

  • Spar Varnish: Spar varnish provides good protection against water, sunlight, and mildew, but its durability may not be as high as spar urethane. It can be prone to cracking, yellowing, and flaking over time due to exposure to the elements.
  • Spar Urethane: Spar urethane is highly durable and offers excellent protection against moisture, sunlight, and temperature variations. It tends to resist cracking and yellowing better than spar varnish, making it a preferred choice for more demanding outdoor applications.

3. Drying Time

  • Spar Varnish: Spar varnish tends to have a slower drying time compared to spar urethane. This can be advantageous in some cases, as it allows for smoother application and reduces the chances of brush strokes or lap marks.
  • Spar Urethane: Spar urethane generally dries faster, which can be beneficial when you need a quicker project turnaround time.

4. Application

  • Spar Varnish: Spar varnish is often brushed on surfaces, and multiple coats are recommended for optimal protection.
  • Spar Urethane: Spar urethane is also applied using a brush, but it can sometimes be sprayed for larger projects. Like spar varnish, multiple coats are advisable for better protection.

5. Odor and Cleanup

  • Spar Varnish: Oil-based spar varnish has a strong odor during application and requires mineral spirits or paint thinner for cleanup.
  • Spar Urethane: Spar urethane, being a synthetic product, usually has a milder odor during application and can be cleaned up with mineral spirits or water, depending on the specific formulation.

6. Indoor vs. Outdoor Use

  • Spar Varnish: While spar varnish can be used both indoors and outdoors, it is more commonly applied to outdoor projects due to its additional resistance to UV light and moisture.
  • Spar Urethane: Spar urethane is specifically designed for outdoor use, but it can also be used indoors on wood surfaces that will experience heavy wear or moisture exposure.

7. UV Resistance

Spar urethane is highly resistant to UV rays, which can cause wood to fade or discolor over time. On the other hand, spar varnish provides less protection against UV rays, which can result in fading and discoloration.

8. Flexibility

Spar varnish is more flexible than spar urethane, which means that it is less likely to crack or peel when exposed to temperature changes or humidity fluctuations.

9. Glossiness

Spar varnish provides a high-gloss finish that gives wood a warm, rich appearance. Spar urethane, on the other hand, provides a low-gloss finish that ranges from satin to semi-gloss, giving wood a more natural appearance.

10. Cost

In terms of cost, spar varnish is usually less expensive than spar urethane. However, this difference in cost should be weighed against the longer-lasting protection and durability provided by spar urethane.

In summary, both spar varnish and spar urethane are effective wood finishes with protective properties. If you’re working on an outdoor wood project that requires excellent durability and UV resistance, spar urethane might be the more suitable choice. However, for indoor projects or less demanding outdoor applications, spar varnish can still provide adequate protection and a beautiful finish.


In conclusion, when it comes to choosing between spar varnish and spar urethane, it is important to consider the specific needs of your project. For projects that require long-lasting protection and durability, such as marine applications, spar urethane is the better choice. For projects that require a more flexible finish with a high-gloss appearance, such as outdoor furniture, spar varnish is a suitable option.

No matter which finish you choose, be sure to follow the manufacturer’s instructions carefully and take the time to prepare the wood surface properly before applying the finish. By doing so, you can ensure that your wood will be protected and look great for years to come.

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