Can Polyurethane be Used Outdoors

Imagine you’ve just finished creating a beautiful outdoor wooden bench. It’s sleek and sturdy, and it perfectly complements the surrounding garden.

Now, you want to ensure that this masterpiece lasts and can withstand the elements – the rain, the sun, and the changing seasons. Here’s where polyurethane comes into the picture.

The Use of Polyurethane

Polyurethane is a polymer, a large molecule of several smaller units linked together. It’s a chameleon in the world of materials, known for its flexibility and adaptability. It can be hard and rigid like plastic or soft and squishy like foam. Polyurethane can take on these various forms based on its manufacture and the specific ingredients.

But why is polyurethane such a popular choice, especially regarding wood protection? Well, it’s all about its unique properties. Polyurethane is highly resistant to temperature variations and water damage, making it a go-to material for insulation, sealants, and wood finishes. It serves as a protective shell, shielding the wood from the potential harm that could be caused by exposure to harsh weather or wear and tear.

When applied to wood, polyurethane acts like a suit of armor. It seeps into the wood’s pores, filling them up and forming a barrier on the surface. This resilient and robust barrier protects the wood underneath from water, sun, and scratches. Not only that, but it enhances the appearance of the wood, giving it a glossy or satin finish that highlights the natural patterns and textures of the material.

Can Polyurethane Be Used Outdoors?

So, we’ve established that polyurethane is a versatile and robust material, ideal for protecting wood. But can it be used outdoors? Can it withstand the harshness of the weather and the changing seasons?

Well, the answer is a resounding yes. Polyurethane, due to its water and temperature-resistant properties, is perfectly suited for outdoor use. It forms a protective shell around the wood, shielding it from the elements and preventing water from seeping in and causing damage. The result? Your outdoor wooden pieces look as good as new for longer, regardless of what Mother Nature has in store.

However, it’s worth noting that not all polyurethanes are created equal. Some are better equipped to handle the great outdoors than others, which brings us to our next point.

Types of Polyurethane for Outdoor Use

When it comes to using polyurethane outdoors, you have a few options. Let’s look at three main types: oil-based, water-based, and water-based oil-modified polyurethane.

Oil-Based Polyurethane

Oil-based polyurethane is the old-school favorite for its durability and beautiful glossy finish. It’s tough, resilient, and can withstand heavy foot traffic, making it an excellent choice for outdoor wooden furniture or decking. However, it tends to yellow over time, which might not be ideal for everyone. Also, oil-based polyurethane takes longer to dry, meaning you’ll need to wait a bit before showing off your woodwork to the world.

Water-Based Polyurethane

Then we have water-based polyurethane. This type is gaining popularity due to its quick-drying time and clear finish that doesn’t yellow over time. It’s also more environmentally friendly, with lower volatile organic compound (VOC) levels. But while water-based polyurethane is great for indoor use, it might not hold up well outdoors. It’s not as durable as its oil-based counterpart and might not provide the same protection against the elements.

Water-Based Oil-Modified Polyurethane

Last but not least, there’s water-based oil-modified polyurethane. As the name suggests, this type combines the best of both worlds. It’s as durable as oil-based polyurethane and has the clear finish and quick-drying benefits of water-based polyurethane. This type could be your best bet for outdoor use, offering excellent protection without compromising on aesthetics.

Understanding Weatherproof Polyurethane

Now that we’ve explored the types of polyurethane fit for outdoor use, let’s dive a bit deeper into the concept of weatherproof polyurethane. You might be wondering, “what makes a polyurethane weatherproof?” Excellent question!

Weatherproof polyurethane is specially formulated to withstand the harsh conditions of the great outdoors. It protects against damaging factors like UV rays, rain, and temperature changes. This polyurethane variant goes beyond merely sealing and protecting the wood and adds a layer of armor against the ever-changing weather.

Imagine you have a beautiful wooden deck, a sturdy picnic table, or a charming garden bench. These outdoor pieces are constantly exposed to sun, rain, snow, and even the occasional hail. Over time, these elements can cause the wood to fade, warp, or rot.

But with weatherproof polyurethane, you add a shield that protects your wooden pieces from these weather-induced damages. It’s like a raincoat for your wood, keeping it dry and protected no matter how hard it pours.

The Durability of Polyurethane Outdoors

As we journey further into outdoor polyurethane, a question arises: “How long will polyurethane last outdoors?” It’s a valid concern. After all, you don’t want to invest time and energy into a project only for it to degrade after a few short years.

The good news is that polyurethane is renowned for its durability. Once applied, it forms a hard, protective shell around the wood that can last for years. However, the exact longevity of polyurethane outdoors depends on several factors.

The Type of Polyurethane

As we’ve discussed earlier, not all polyurethanes are created equal. Oil-based polyurethanes generally offer longer-lasting protection compared to water-based ones. Water-based oil-modified polyurethane combines both strengths, providing a durable and aesthetically pleasing finish.

The Severity of Weather Conditions

The harsher the weather conditions, the faster your polyurethane finish might wear down. If you live in an area with intense sun, heavy rainfall, or extreme temperatures, you might need to reapply polyurethane more often.

Maintenance and Upkeep

Regular maintenance can significantly extend the life of your polyurethane finish. This includes cleaning the surface regularly, checking for signs of wear and tear, and reapplying a new coat of polyurethane when needed.

In general, with proper care and maintenance, a good coat of polyurethane should last anywhere from 10 to 15 years. But remember, the key to longevity is regular maintenance and prompt action at the first sign of wear.

Applying Polyurethane Outdoors

Embracing the use of polyurethane outdoors requires knowledge of the application process. It’s not rocket science, but some finesse and know-how can go a long way. Here’s a step-by-step guide on how to go about it:

  1. Preparation: Start with a clean, smooth surface. Sand the wood with medium-grit sandpaper, followed by fine-grit sandpaper. Remove all dust with a tack cloth.
  2. Application: Using a high-quality, natural-bristle brush, apply the polyurethane toward the wood grain. Try to maintain a wet edge to prevent overlapping marks.
  3. Drying: Allow the polyurethane to dry completely. This process can take anywhere from a few hours to overnight, depending on the specific product and weather conditions.
  4. Sanding: Once dry, lightly sand the surface with fine-grit sandpaper. This helps the next coat adhere better. Remember to remove dust with a tack cloth after sanding.
  5. Second Coat: Apply a second coat of polyurethane, again following the grain of the wood. Let it dry thoroughly.
  6. Repeat: Depending on your desired level of protection, you may want to repeat the process for a third or even fourth coat.

Remember, the best results come from patience and attention to detail. Avoid applying polyurethane in direct sunlight or extreme temperatures, as this can cause it to dry too quickly and result in a less-than-optimal finish.

Common Mistakes When Using Polyurethane Outdoors

While polyurethane can work wonders for your outdoor wood projects, common mistakes can hinder the desired results. Let’s explore some of these pitfalls and how to avoid them:

Using Interior Polyurethane Outside: This is a classic misstep. Interior polyurethane lacks UV protection and durability to withstand harsh outdoor conditions. Always ensure you’re using a product designed for outdoor use.

Applying Polyurethane to Dirty or Wet Wood: Polyurethane needs a clean, dry surface to adhere properly. Using it on dirty or damp wood can lead to an uneven finish and reduce effectiveness.

Applying Inappropriate Conditions: As mentioned earlier, extreme temperatures or direct sunlight can affect the drying process and final result. Try to apply polyurethane in mild, dry conditions.

Skipping Sanding Between Coats: This crucial step helps the subsequent coat adhere better, resulting in a smoother, more durable finish.

Polyurethane and Outdoor Furniture

Outdoor furniture can take a beating from the elements. Polyurethane, with its ability to provide a robust protective barrier, is an excellent choice for defending your outdoor pieces. It adds a glossy sheen, enhancing the beauty of the wood, and it’s durable enough to withstand rain, snow, and even the blazing sun.

But what about specific brands, like Minwax polyurethane? Can they be used outdoors? In general, Minwax produces several types of polyurethane suitable for outdoor use. However, always ensure that the product you choose specifically states it is designed for outdoor use.

Some Minwax products are for interior use only and lack UV protection and water resistance needed for outdoor conditions. So, yes, you can use Minwax polyurethane outdoors, but ensure it’s the right kind for the job.

Polyurethane in Different Weather Conditions

Polyurethane is like the Superman of wood finishes, providing a shield against various weather conditions. But how does it fare in the sun, rain, or snow?

Let’s start with sunlight. Polyurethane for outdoor use contains UV blockers that protect the wood from the sun’s harmful rays. This prevents the wood from turning gray or bleached over time. However, the finish may require reapplication every few years to maintain this UV protection.

In rainy conditions, polyurethane stands strong. Its waterproof finish creates a seal that prevents water from penetrating the wood. This helps prevent warping or rotting, ensuring your outdoor projects stay intact and look great for years.

Cold and snow don’t phase polyurethane, either. It’s designed to withstand freezing temperatures and the wetness of melting snow. However, temperature fluctuations can cause the wood to expand and contract, which might lead to cracking over time. Regular maintenance can help mitigate this issue.

Best Outdoor Polyurethane for Wood

When protecting outdoor wood, not all polyurethane products are created equal. Here are a few that stand out for their superior performance.

  1. Minwax Helmsman Spar Urethane: This product is designed for outdoor wood exposure. It contains special UV blockers and is water-resistant, perfect for protecting wood from the elements. It also provides a beautiful, glossy finish.
  2. Varathane Spar Urethane: Varathane offers exceptional durability and protection against UV light, making it ideal for outdoor furniture, doors, and windows. It’s available in various sheens and is known for its fast-drying formula.
  3. General Finishes Exterior 450: This water-based topcoat is built to be durable in outdoor conditions. It’s suitable for vertical surfaces, such as doors or outdoor furniture. Its built-in UV stabilizers protect the wood from the sun.

Polyurethane Wood Sealant for Outdoor Use

If you’re wondering whether polyurethane protects wood outdoors, the answer is a resounding yes. Polyurethane acts as an excellent sealant for outdoor wood applications. It provides a clear, hard finish that protects wood from moisture, sun damage, and wear and tear.

Polyurethane seals the wood and enhances its natural beauty, making the grain and color pop. It’s available in several finishes, from glossy to satin, so you can choose the look that best suits your project.

However, it’s important to note that outdoor polyurethane is not a one-and-done solution. Although it provides robust protection, it does wear over time and will need reapplication every few years, especially in harsh weather conditions. Regular maintenance will ensure your outdoor wood projects remain protected and look their best for years.

Popular Brands of Outdoor Polyurethane

Choosing the right brand of polyurethane can make all the difference in your outdoor wood projects. Here are some popular ones that you might consider:

  1. Minwax: Known for its quality wood finishing and wood care products, Minwax offers a range of outdoor polyurethanes, including the well-regarded Helmsman Spar Urethane.
  2. Rust-Oleum: A big name in protective paints and coatings, Rust-Oleum’s Varathane line of polyurethane provides excellent UV and weather protection for outdoor wood.
  3. General Finishes: This brand is praised for its high-quality finish and durability. Their Exterior 450 outdoor polyurethane is a favorite among woodworkers.
  4. Deft: Deft’s water-based polyurethane is known for its easy application and excellent durability, making it another good option for outdoor use.

Each of these brands offers its unique features and benefits, so take the time to research and choose one that best meets your project needs.

Frequently Asked Questions About Outdoor Polyurethane

To wrap things up, let’s tackle some of the most common questions about using polyurethane outdoors:

  • Can interior polyurethane be used outside? The short answer is no. Interior polyurethane lacks the UV blockers and weather-resistant properties found in outdoor formulas. Using it outdoors could result in a subpar finish that deteriorates quickly.
  • What happens if you use polyurethane outside? Using the correct type—outdoor polyurethane—will provide a hard, protective layer that guards against weather and wear. If you mistakenly use an indoor formula, it may not hold up well against the elements and could peel or crack over time.


In our journey through polyurethane and its outdoor applications, we’ve covered a lot of ground. We’ve learned about the different types of polyurethane suitable for outdoor use, their durability, and how to apply them correctly. We’ve also examined the top polyurethane brands and answered some common questions about its outdoor use.

Remember, the key to a successful outdoor wood project lies in choosing the right type of polyurethane and applying it properly. With this knowledge, you’re well-equipped to make your outdoor wood projects shine with resilience and beauty. So, why wait? Get started on your project today, and let the world marvel at your craft!