When it comes to woodworking projects, choosing the right protective coat is essential to ensure the longevity and beauty of your creation. Two commonly used products for this purpose are spar urethane and polyurethane. While they may sound similar, there are key differences between the two that can make choosing the right one a bit tricky. In this article, we will delve into the main differences between spar urethane and polyurethane, and when to use each one for the best results.
What is Spar Urethane?
Spar urethane is a special type of varnish that was originally designed for boats. Its predecessor, spar varnish, was used on the spars of sailing boats to protect them from water and UV light. With the addition of urethane plastic to the formula, spar urethane became suitable for both interior and exterior use. This makes it a great choice for woodworking projects that are exposed to moisture and sunlight. There are two main types of spar urethane - oil-based and water-based.
Oil-Based Spar Urethane
Oil-based spar urethane is a durable finish that provides excellent protection against scratches, dents, and chemical spills. While it is easy to apply and dries relatively quickly, it does tend to yellow over time. Other pros of oil-based spar urethane include its scratch and water resistance, as well as its ability to dry quickly and provide UV protection. However, it does not dry as hard as polyurethane and may need to be reapplied occasionally.
Water-Based Spar Urethane
Water-based spar urethane, on the other hand, is also a durable finish that offers scratch and water resistance. It dries clear and remains clear, without yellowing over time. It is also easier to clean up as compared to oil-based spar urethane. However, it may not provide the same level of protection against UV rays as its oil-based counterpart.
What is Polyurethane?
Polyurethane is a durable and water-resistant finish that dries very hard. It can be used on a wide range of furniture, floors, tables, fences, and other wooden surfaces that require protection from water and scratches. Polyurethane comes in two main types - oil-based and water-based.
Oil-Based Polyurethane
Oil-based polyurethane is known for its warm tone and tendency to yellow over time. It provides a thick coat that lasts for a long time and offers excellent scratch, chemical, and water resistance. It dries very hard and can withstand a lot of wear and tear. However, it takes a long time to dry, emits high quantities of volatile organic compounds (VOCs), and may require multiple coats with lengthy drying times in between.
Water-Based Polyurethane
Water-based polyurethane, on the other hand, dries clear and remains clear without yellowing over time. It is also resistant to scratches, chemicals, and water. It dries faster than oil-based polyurethane and emits fewer VOCs, making it a safer option for both people and the environment. However, it may not be as durable as oil-based polyurethane and may require more frequent reapplication.
Spar Urethane vs Polyurethane - A Feature Comparison
Now that we understand the basics of spar urethane and polyurethane, let’s compare them in terms of various features:
1. Ease of Application
Both spar urethane and polyurethane can be applied in a similar manner. The application process involves scuffing the surface, cleaning it, applying the first coat, waiting for it to dry, and then adding subsequent coats as needed. Some people find spar urethane easier to apply due to its softer material and lesser visibility of brush strokes. However, water-based polyurethane does not have the same issues with brush strokes.
2. Drying Times
Spar urethane generally dries faster than polyurethane. Oil-based spar urethane can be ready for a subsequent coat in just four hours, whereas polyurethane may take up to 24 hours for a single coat to dry. However, it is important to note that there are fast-drying oil-based polyurethane options available that dry in as little as four to six hours. Water-based versions of both spar urethane and polyurethane have shorter drying times, typically two hours.
3. Toxicity
Polyurethane, especially oil-based, emits high quantities of VOCs, which can be harmful to the environment and may irritate the eyes, lungs, and skin during application. Spar urethane also emits VOCs, but typically at lower levels than polyurethane. Water-based versions of both products tend to have lower VOC emissions and are considered safer for use.
4. Finish Durability
Polyurethane is known for its durability and ability to maintain a hard finish for many years. Spar urethane, on the other hand, is designed to have a bit of flexibility to accommodate changes in the wood due to weather conditions. While polyurethane can last for one to two decades, water-based spar urethane may last around five years and oil-based spar urethane may last even longer. Polyurethane is generally considered to be more durable than spar urethane.
5. Ambering
Ambering refers to the development of a yellow or amber hue in the finish over time. Oil-based finishes, including both polyurethane and spar urethane, tend to amber as they age. This can be undesirable, especially on lighter woods or light paint colors. Water-based polyurethane remains clear and does not amber, while water-based spar urethane may amber on light stains and woods. It is important to test water-based spar urethane on an inconspicuous part of the surface to ensure it does not yellow before applying it.
6. Protection from Elements
Spar urethane is designed to withstand the elements and is particularly well-suited for exterior use. It can handle UV rays without the wood turning gray and can withstand a lot of moisture. Polyurethane, especially exterior polyurethane, can provide UV protection as well, but it may not be as resilient to moisture as spar urethane. Interior polyurethane does not offer the same level of UV protection as spar urethane.
7. Versatility
Polyurethane is a versatile product that can be used on various wooden surfaces, including floors, tables, and furniture. Spar urethane, on the other hand, is not recommended for high-traffic areas such as wood floors. It is better suited for surfaces that do not require a rock-hard finish, such as outdoor furniture or woodwork exposed to moisture and sunlight.
Conclusion
In conclusion, both spar urethane and polyurethane have their own unique advantages and disadvantages. The choice between the two largely depends on the specific requirements of your woodworking project. If you need a finish that is water-resistant and can withstand UV rays, spar urethane may be the better choice. On the other hand, if you require a durable, hard finish that is versatile and can be used on various wooden surfaces, polyurethane is a great option. Consider the features and characteristics of both products before making your final decision.
