Is Polyurethane OK For Exterior Use? Will it Yellow

Do you want to protect your outdoor workpieces with a durable sealant but are not sure if polyurethane is the right choice?

Yes, polyurethane is the right choice for exterior use as it provides good resistance to environmental factors such as moisture, sunlight, heat, cold, etc. However, it is important to select specially formulated UV protection polyurethane for applications that are subjected to sunlight for prolonged durations.

We tested polyurethane in outdoor conditions and prepared a detailed guide to help you make the right decision for your project.

Polyurethane for Exterior Use: Is it a Good Choice?

When it comes to finishing materials for exterior projects, polyurethane is a popular choice because of its many benefits.

Polyurethane is a synthetic material known for its durability, resistance to wear and tear, and ability to protect surfaces from damage caused by water, chemicals, and UV radiation.

But whether or not polyurethane is the right choice for your particular exterior project depends on a number of factors.

One of the main factors to consider is the level of exposure to the elements that your project will face.

Oil-based poly is a good choice for outdoor projects that may expose to moderate wear and tear, water, chemicals, and UV radiation, as it offers better protection than water-based polyurethane.

Another factor to consider is the type of surface you’ll be applying the polyurethane to.

Polyurethane works best on surfaces that are smooth, clean, and dry.

If the surface is uneven, dirty, or damp, the polyurethane may not adhere properly and may not provide the level of protection you need.

Ultimately, the decision to use polyurethane for your exterior project comes down to a balance of cost, convenience, and effectiveness.

If you need a durable, long-lasting finish that provides good protection against the elements, and you’re willing to invest the time and effort required to apply the polyurethane properly, then it may be the right choice for you.

Is Polyurethane Waterproof?

Polyurethane finish after prolonged exposure to moisture
Polyurethane finish after prolonged exposure to moisture

Polyurethane can be an effective waterproofing material that can provide a certain level of protection against water damage.

It can also help to extend the lifespan of the surface it’s applied to, making it a smart investment for many DIY projects.

However, it’s worth noting that polyurethane is not completely waterproof.

Over time, exposure to water can cause the material to break down or wear away, which can compromise the protection it provides.

This is especially true if the surface underneath the polyurethane is not properly prepared or if the polyurethane is not applied correctly.

For best results, it’s important to follow the manufacturer’s instructions carefully and to take steps to ensure that the surface is clean, dry, and properly primed before applying the polyurethane.

Is Polyurethane Resistant to UV Radiation?

Polyurethane finish before and after exposure to Sunlight
Polyurethane finish before and after exposure to Sunlight

Polyurethane is known for its durability and resistance to wear and tear, but it’s also important to consider its resistance to UV radiation when using it for exterior projects.

UV radiation can cause materials to fade, discolor, and deteriorate over time, which can compromise the appearance and effectiveness of your project.

Fortunately, polyurethane is generally quite resistant to UV radiation, making it a popular choice for exterior projects that will be exposed to sunlight.

However, it’s important to note that not all polyurethane products are created equal in terms of their UV resistance.

Some products are specifically formulated for exterior use and contain additional UV inhibitors to help protect against sun damage, while others may not be suitable for use in areas with high levels of sun exposure.

To ensure that you’re getting the best possible UV protection from your polyurethane finish, look for products that are specifically designed for exterior use, such as UV-resistant ones.

It’s also a good idea to take steps to minimize the amount of direct sunlight that your project will be exposed to, such as by providing shade or applying a sealant over the polyurethane coat.

Is Polyurethane Resistant to Temperature Changes?

Polyurethane workpiece after exposure to heat for prolonged time
Polyurethane workpiece after exposure to heat for a prolonged time

Polyurethane is a versatile material that is commonly used in many wooden surfaces, including exterior projects that are exposed to harsh temperatures.

While polyurethane is quite durable and resistant to temperature changes, it has limitations.

One of the advantages of polyurethane is its ability to withstand temperatures from extremely hot to freezing cold.

This makes it a popular choice for outdoor projects exposed to varying temperatures.

Also, polyurethane is pliable and can expand or contract as temperatures fluctuate, which helps to prevent cracking and other types of damage.

Unfortunately, exposure to prolonged periods of extreme heat or cold can cause the material to break down, compromising its effectiveness and longevity.

Besides, if the wood surface is not properly prepared or if the polyurethane is not applied correctly, it can easily flake off under temperature changes.

What to Know Before Buying Polyurethane for Outdoor Applications

Polyurethane exposed to sunlight
Oil-based wipe on polyurethane

Resistance to UV Radiations

UV radiation can cause a finish to fade and deteriorate over time, so it’s important to choose a polyurethane resistant to UV radiation.

Look for products that are specifically formulated for outdoor use and that contain UV inhibitors.

Ease of Application

Another important factor to consider is how easy the polyurethane is to apply.

Some polyurethane products may require multiple coats or specialized equipment, while others can be applied with a brush or roller.

When working on an outdoor project that is fixed in place, consider the ease of application.

While a bristles brush is best suited to reach even the smallest corners of the workpiece, wipe-on polyurethane is much easier to apply to large surfaces.

Apart from that, you can also opt for one-coat polyurethane. It is a thicker polyurethane that does not require multiple coats to get the needed result.

Time to Dry

If you use polyurethane outside, you need to think about how fast it dries. Some types dry fast, while others take a long time to harden.

You don’t want dust or rain to spoil your polyurethane finish or your workpiece.

So, use quick-dry polyurethane outside. It will dry fast and stay clean.

Final Thoughts

You can use polyurethane outside, but you need to choose the right type for your weather.

Oil-based polyurethane is good for the outside because it lasts longer and keeps out water.

Also, you should put a new coat of polyurethane on your workpiece every half year.

Sand the damaged poly, wipe it clean with mineral spirit, let it dry, and apply a new coat of poly to maintain it properly.

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Frequently Asked Questions (FAQ)

Can polyurethane be applied over painted surfaces?

Yes, polyurethane can be applied over painted surfaces as long as the paint is fully cured and the surface is properly prepared. Sanding and cleaning the surface prior to application can help ensure proper adhesion.

Can polyurethane be used on all exterior surfaces?

Polyurethane can be used on a variety of exterior surfaces, including wood, concrete, and metal. However, it’s important to choose a product specifically formulated for the surface you are coating and to prepare the surface properly before application.

Can you use a spray gun to apply polyurethane?

Yes, you can use a spray gun to apply polyurethane. However, it is only suitable for large projects where the long set up time is compensated by the time saved in applying polyurethane over the workpiece.