Spar Urethane Vs. Polyurethane: What’s Better for My Project?

When finishing your woodworking project, choosing the right type of protective covering is crucial. With so many options on the market, deciding which is best suited for your project can be challenging. Two popular choices among woodworkers are spar urethane and polyurethane. While both offer excellent protection and durability, their properties and application methods differ.

The decision to use either spar urethane or Polyurethane should be based on several factors. These factors include the type of wood used, the project’s location (indoor or outdoor), the desired level of durability, and personal preferences. It is essential to consider these factors to make an informed decision carefully.

This article provides comprehensive information concerning the differences, applications, durability, and drying times of spar urethane and Polyurethane.

Spar Urethane Vs. Polyurethane

What Are the Characteristics and Differences Between Spar Urethane and Polyurethane?

To make an informed decision for your project, it is essential to clearly understand the unique characteristics and distinctions between urethane and Polyurethane. Let us delve into their properties and differences to gain a deeper understanding.

Characteristics of Polyurethane

Polyurethane is a versatile, durable coating with a hard and protective finish. Some of the critical characteristics of Polyurethane include the following:

  • Durability: The durability and resilience to wear and tear of Polyurethane are well recognized. It is resistant to dents, scratches, and other sorts of harm.
  • Water Resistance: Polyurethane is water-resistant, which makes it an excellent choice for use in humid environments or areas prone to water damage.
  • Chemical Resistance: Polyurethane is perfect for use in industrial environments because of its resistance to various chemicals.
  • Clarity: Applying polyurethane results in a transparent coating that effectively showcases the innate elegance of wood grain.

Characteristics of Spar Urethane

Spar Urethane is a specific type of Polyurethane designed for outdoor use. Some of the key characteristics of Spar Urethane include:

  • UV Resistance: Spar Urethane is formulated to provide excellent protection against the damaging effects of sunlight, including fading, yellowing, and cracking.
  • Water Resistance: Like Polyurethane, Spar Urethane is water-resistant, which makes it ideal for use in outdoor environments where it may be exposed to rain and humidity.
  • Flexibility: Spar Urethane is more flexible than other types of Polyurethane, which allows it to expand and contract with changes in temperature and humidity without cracking or peeling.
  • Glossiness: It dries to a high-gloss finish, which gives it a shiny and polished appearance.

What Are the Application Differences Between Spar Urethane and Polyurethane?

Having acquired a fundamental knowledge of Spar Urethane and Polyurethane, it is now time to explore their distinctive differences in terms of application.

Outdoor and Indoor Applications

Spar Urethane is a specialized protective coating designed to safeguard wood surfaces from environmental hazards, making it an excellent choice for outdoor use. In contrast, Polyurethane is typically recommended for indoor applications, as it is not resistant to ultraviolet rays and can deteriorate when exposed to sunlight.

Gloss Level

Polyurethane typically has a higher gloss than Spar Urethane, making it perfect for indoor surfaces such as furniture, floors, and cabinets. On the other hand, Spar Urethane has a lower gloss level, which is more suitable for outdoor surfaces like decks, fences, and boats.

Drying Time

In terms of drying duration, Spar Urethane exhibits a lengthier phase when compared to Polyurethane. The drying process of Spar Urethane is contingent on the prevailing humidity and temperature factors, with some instances taking up to a span of 24 hours to complete, in contrast to Polyurethane, which typically concludes within a period of 4-6 hours.


Spar Urethane is designed to be applied in thick coats, which provides better protection for outdoor surfaces. Conversely, Polyurethane is typically used in thin coats, allowing for faster drying and a smoother finish.

Which Finish Is Better for Your Project?

When choosing between Spar Urethane and Polyurethane for your project, there are a few factors to consider. Here are some scenarios to help you decide which finish is better suited for your project:

Outdoor and Indoor projects

As mentioned, Spar Urethane is the clear winner if you work on an outdoor project, such as a deck or patio furniture. Its UV-resistant formula protects against sunlight and weather damage, making it ideal for outdoor use.

For indoor projects, both finishes can be used depending on the type of project. If you’re working on something that requires high durability, such as flooring or kitchen cabinets, then Polyurethane is the better choice. Spar Urethane may be the better option if you’re working on something that requires a more natural look and feel, such as wooden furniture or decorative pieces.

Ease of application

Both finishes are easy to apply, but Polyurethane has a shorter drying time and can be sanded and recoated within a few hours. This makes it a good choice for projects that require multiple coats.


Spar Urethane is the way to go if you want a low-maintenance finish. Its UV-resistant formula protects against weather damage and only requires occasional cleaning to maintain its shine. On the other hand, Polyurethane may require periodic sanding and recoating to maintain its appearance.

Which is better for my woodworking project, Spar Urethane or Polyurethane?

When deciding between Spar Urethane and Polyurethane for your woodworking project, consider the unique qualities of each. Spar Urethane is known for its UV protection, making it ideal for outdoor use. On the other hand, Polyurethane offers greater resistance to abrasion and chemicals. Think of it as a wood hardener compared with stabilizer.

Can I Use Emery Cloth to Prep Surfaces Before Applying Spar Urethane or Polyurethane?

When preparing surfaces before applying spar urethane or polyurethane, emery cloth uses and grades are important to consider. Using a fine grade emery cloth, you can gently sand the surface to create a smooth, even finish. This will ensure better adhesion and a professional-looking final result.

How to Apply Spar Urethane and Polyurethane?

Having determined the most suitable option for your project, it is now imperative to acquire knowledge on how to apply it effectively. The application process is crucial to attaining a polished and consistent finish on your project.

Preparing the Surface

Before you apply any finish, it’s crucial to prepare the surface properly. Begin by sanding the surface with fine-grit sandpaper to remove any imperfections or roughness.

Use a tack cloth to remove the sanding process’s dust and debris. Clean the wood with mineral spirits or a similar solvent if it has any stains or oils. Allow the surface to dry completely before proceeding.

Applying Spar Urethane

When applying spar urethane, a natural bristle brush is best to avoid leaving brush marks. Start by applying a thin and even spar urethane coat, working toward the wood grain.

To ensure a flawless finish, it is paramount to exercise caution when brushing. Excessive brushing may result in unsightly bubbles and streaks. It is highly recommended to allow the initial coat to cure before the subsequent application fully. For maximum protection, it is advisable to administer two to three coats of spar urethane.

Applying Polyurethane

Polyurethane can be applied using a natural bristle brush, a foam brush, or a sprayer. When using a brush, begin by loading it with a small amount of Polyurethane and apply it toward the wood grain.

Avoid over-brushing, as this can cause bubbles and streaks. Allow the first coat to dry completely before applying the next coat. It’s best to apply two to three coats of Polyurethane for optimal protection.

Tips for Applying Spar Urethane and Polyurethane

  • Keep the room temperature between 55-90°F and the humidity level between 40-60%.
  • Stir the finish thoroughly before use, but avoid shaking it to prevent bubbles from forming.
  • Apply the finish in thin and even coats to avoid drips and runs.
  • Sand lightly between coats with fine-grit sandpaper to ensure adhesion.
  • Wait for each coat to dry completely before applying the next coat.
  • Avoid applying the finish in direct sunlight or windy conditions.
  • Clean your brushes or sprayer thoroughly with mineral spirits or paint thinner after use.

Which is a Better Fit For My Project: Spar Urethane Vs. Polyurethane?


The selection process between Spar Urethane and Polyurethane is contingent upon many variables, including but not limited to the specific nature of the undertaking, how it is to be applied, and the degree of resilience deemed necessary.

If you’re working on an outdoor project exposed to the elements, Spar Urethane is the best option due to its UV resistance and ability to withstand moisture. On the other hand, if you’re working on an indoor project that doesn’t require exposure to harsh weather conditions, Polyurethane is the more cost-effective option.

Both finishes offer excellent protection to wood surfaces and enhance their appearance, but selecting the right one for your project can make a significant difference in the longevity of your work. Ultimately, the choice between the two depends on the specific requirements of your project and personal preferences.

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