9 Best Exterior Polyurethanes: A Complete Guide

Exterior Polyurethanes for wood projects

One of the best things you can apply to improve the longevity and appearance of your wooden items is a smooth and thick coat of polyurethane. Through this one easy step, you can give your surface a much-needed shine while also saving it from moisture. However, when it comes to exterior polyurethanes, they must be more durable than interior polyurethanes and should also have the ability to survive even in the harshest conditions.

 Our pick for a product that has all the qualities mentioned above is the ZAR Exterior Oil-Based Polyurethane. Nonetheless, oil-based products are just one category of exterior polyurethanes and may not be what you’re looking for entirely. If you have just started out, getting the best, or let alone the right exterior polyurethane, can be tough. Therefore, we have reviewed the nine best exterior polyurethanes for your wood projects.

What Is Polyurethane?

Polyurethane is a varnish that is super-tough in nature. It has tiny microscopic chains of resin molecules that bond closely with one another when it dries. As a result, you get a finish that is much more water, solvent, and abrasion-resistant. It is a quality most traditional varnishes lack.

RUST-OLEUM Ultimate Oil-Based Spar Urethane

The RUST-OLEUM Ultimate Oil-Based Spar Urethane is one of the best choices for exterior polyurethane if you are on a budget. It is a great bargain as it is not only Rust-Oleum but also budget-friendly. As expected of exterior polyurethanes, it is resistant to UV lights, which is a source of discoloration. Moreover, it can also withstand rigorous activities in the outdoor environment.


  • Resistant to mildew and mold
  • Resistant to any elements of moisture due to its oil-based nature
  • Can withstand harsh outdoor conditions
  • The formula is durable, and it dries in 2 hours
  • Can cover an area as big as 190 square feet per gallon
  • Comes with a UV and weather-resistant formula
  • Gives a clean and gloss finish
  • Suitable for protecting outdoor fences and furniture
  • Great value for money


  • Turns yellow with time
  • Takes slightly longer than other products to dry

Deft Defthane Interior Exterior Clear Polyurethane Gloss

As the name states, this product is suitable for both exterior and interior environments. Additionally, it also gives a secure finish to your wooden structure. After application, it dries to give you a robust finish that is also water-resistant. If you’re facing trouble understanding how to apply polyurethane for the best results, it is one of the easiest choices for you. Since it has a great consistency, it also helps minimize any remains of brush marks.


  • Can be applied to a variety of surfaces like varnished and lacquered surfaces along with stained wood
  • Has a really good consistency
  • Dries in just 30 minutes
  • Recoating takes 6 hours
  • Helps minimize brush marks
  • Can cover an area as extensive as 600 square feet per gallon
  • Can be used for both exterior and interior surfaces

The Con

  • Takes a long time to cure

ZAR Exterior Oil-Based Polyurethane

It’s a product that gives tints the surface you apply it on, leaving it with a satin finish. Due to this property, it brings out true, natural colors of your wooden surface. The formula guarantees both protection and beauty. If compared to its water-based counterparts, it gives a much shiny finish. It is a product you should consider if you are looking for something to give your surface a classy and contemporary finish.


  • Contains elements to block UV light
  • Contains anti-oxidants that resist yellowing
  • Brings out the wood’s natural color
  • Gives a tough, dry finish
  • Twice as durable as its water-based counterparts

The Con

  • Has a limited shelf life

ZAR Exterior Water-Based Polyurethane

This water-based product is one of the best options for your surface as it is also water-resistant. Even though most great exterior polyurethanes are water-resistant, this stands out the most as it can also withstand heavy rain. However, it is not recommended for usage underwater. In comparison to similar products in the market, it is a little thinner. Moreover, since very few chemicals are involved in making this product, you won’t have to deal with a strong odor.


  • Protects against UV rays
  • Has anti-oxidants that prevent discoloration of your surface
  • Resistant to any weather condition
  • Recommended by leading door manufacturers
  • Can be cleaned with soap and water
  • Provides marine-grade finish
  • Has a long shelf life


  • Susceptible to bubbling
  • Heavy on the pocket

RUST-OLEUM 207008 Spar Varnish, Clear, Polyurethane

Over time, this product has built its reputation for being a reliable product. Its formula provides your wooden surface protection against water, sunlight, and chemical above the waterline. Moreover, it has a flexible coating that contracts and expands depending on the variation in weather conditions. Besides, it’s two times more durable than a standard wood finish.


  • Works best for wood surfaces above the waterline, such as railings, wood furniture, and trim
  • Covers an area of up to 150 square feet
  • Takes only 2 hours to dry
  • Flexible to changes in weather
  • Leaves a beautiful gloss finish as it cures into a crystal clear varnish
  • Affordable and durable
  • Resistant to UV, mildew, and salt.

The Con

  • Few complaints of a white residue during usage of the formula

Deft Interior Exterior Water-Based Polyurethane Finish Gloss, Quart

This water-based formula comes with a clear protective topcoat that protects water and UV lights. Its amazing sanding quality makes it stand out as one of the best exterior polyurethanes as it does not require a sealer. Moreover, it is also a great companion to the environment as it has low levels of VOC. In addition, it has a low odor and does not discolor.


  • Can be used on both interior and exterior wood surfaces
  • Can easily be applied using a spray, pad, and brush
  • Easy to clean
  • Dries in 2 hours
  • Recoating can be done after just 2 hours
  • Lasts longer than the water-based polyurethane
  • Contains low VOCs and low odor
  • Protects against UV light

The Con

  • The formula tends to get yellow, as per some users

Minwax Helmsman Indoor/Outdoor Spar Urethane

has a tendencytendsou can use this clear coating formula for both interior and exterior wooden surfaces. Its gallon-sized cans are comparatively better than the quart-sized cans. This product was developed to deal with the harshest outdoor conditions.

Moreover, it also contains UV blockers that prevent it from getting yellow after staying in the sun. Additionally, the formula protects it from flaking and peeling over time. Its special oils make it easy to deal with temperature variations.


  • Gives and maintains a crystal clear finish
  • Does not change the paint color underneath
  • Dries quickly
  • Has UV blockers
  • Good value for money


  • Not suitable for projects that require small corrections since it dries quickly
  • The finish can be ruined if you use a brush on the hard coating
  • Thin consistency due to which it can soak into certain surfaces
  • Difficult to use on foam and soft, porous wood

RUST-OLEUM Ultimate Water-Based Spar Urethane

The formula of this product is quite similar to RUST-OLEUM Ultimate Oil-Based Spar Urethane. However, the only quality that sets it apart is the fact that it’s water-based. It gives your wooden surface a long-lasting and beautiful, rock-hard finish. In addition, it is quite hard to damage any surface with this coating, and it is also very clear, as opposed to its oil-based counterpart.


  • Takes only 30 minutes to dry
  • Ready for recoating after only 2 hours
  • Fewer chances of yellowing with time
  • Durable for many outdoor wood surfaces such as doors, furniture, fences, windows, etc.
  • Has a low odor and can easily be cleaned up using water and soap
  • Can cover up to 87 square feet per quart
  • Gives a glossy finish and is water and UV light-resistant

The Con

  • Can leave streaks on the wood surface

TotalBoat Halcyon Marine Varnish

This water-based product is one of the most durable exterior polyurethanes. It is also quite popular and one of the most recommended products among marine fishing product consumers.

 A unique feature of this product is the Halcyon Gloss Marine Varnish that gives your wooden surface a long-lasting and lustrous finish. Furthermore, it also dries fast and allows you to apply five coats each day without sanding in between.


  • Improved depth and clarity of the finish after every coat
  • Can be used on both interior and exterior surfaces above the waterline
  • Has low levels of VOC and is water-based
  • Easy to maintain and cures into a glossy, hard finish
  • Dries faster
  • Resistant to UV light and weather changes
  • Has excellent flexibility and adhesion that makes it contract and expand naturally
  • Does not have harsh fumes

The Con

  • Can be a little tricky to apply

How to Apply Polyurethane

Once you have purchased the desired product, the next step is to understand how to apply polyurethane. There are a few steps to follow to apply it successfully.

Get the Wood Ready

To obtain ideal results, make sure to clean the surface before you start. Next, choose the right polyurethane finish that suits your surface needs best. It is always best to sand your surface using sandpaper and if the wood is open-grain, seal it with wood grain filler before applying the polyurethane.

This technique ensures that you get a smoother finish. Before splashing on more polyurethane, get rid of any dirt by cleaning the wood thoroughly. There are various methods to apply the product. Some of the ways are:

  • By using a vacuum with a tack cloth
  • By using a rag dipped in spirits (especially if you are using an oil-based polyurethane)
  • By using a cheesecloth dipped in alcohol ( especially if you are using a water-based polyurethane

How to Apply Oil-Based Polyurethane

Since oil-based polyurethanes have a thicker consistency, experts recommend that you use a thinner and thin the solution. You can use naphtha or mineral spirits as your thinner but check if it works well with your polyurethane. If your polyurethane has a thin consistency, it will help you coat all surfaces better.

Moreover, you can use a fine bristled brush to apply these types of exterior polyurethanes. Make sure to buy a good quality bristled brush, or you may cause brush marks on your wooden surface. To use your exterior polyurethane better, use the brush on it gradually and run the brush strokes parallel to your wood. Avoid bubbles on the surface by using straight strokes and using enough finish to coat your exterior surfaces well.

The best way to apply polyurethane is to apply the first coat and wait till it fully dries. Following that, sand the surface by going in the opposite direction of your grain pattern. It is better to sand the surface with 320-grit sandpaper. Be careful while sanding as doing it through too thin a coat can hard the wood under. For the second coat, use a vacuum with a tack cloth.

To get the best possible protection from your polyurethane paint, always repeat the steps. To avail the complete benefit of your coat, use the least amount for both coats. With each coat, the next one appears better and smoother. For an adequate amount of shine on the surface, try rubbing the coat with steel wool and applying paste wax. 

How to Apply Water-Based Polyurethane

Working with water-based polyurethanes is way different than working with their oil counterparts. If you apply water-based polyurethane to an oil-based surface, roughen the wood surface first by using some synthetic steel wool. This will prevent the polyurethane from bleeding out.

The process of applying your polyurethane is quite similar to the oil-based application. You can use a fine bristle brush or a foamy cloth to apply a clear coat of your exterior polyurethane. As you are applying it, keep the grain’s appearance in mind and do not use the product excessively.

Generally, the first coat dries faster than the second. The next coat should only be applied when the one before that is completely dry. You may, however, be required to sand during your applications, and to learn how to do it, always refer to the instructions given on the polyurethane can. In the end, irrespective of the size of your wooden surface, pre-plan to apply at least three coats of your product.

How to Use Spray-on and Wipe-on Polyurethane Types

The biggest advantage of polyurethane is that you can spray or wipe it on your wooden surface. The paint you apply through the spray-on method eventually becomes thin. Both wipe-on and spray-on polyurethane can be used in your home to protect surfaces. If you’re a beginner wondering how to apply polyurethane, use a lint-free cloth to help the paint seep into all corners.

Once you have sprayed it onto the surface, it works like spray paint, and a thin layer of polyurethane appears. Using a lint-free cloth, wipe-on exterior polyurethane can also be applied to surfaces. Some experts believe that to ensure a smoother finish, it is best to apply a thinner film of the product on top.

Types of External Polyurethanes

Water-Based Polyurethane

 It consists of a milky formula that gives you a clear finish and is also used by experts who prefer the wood’s natural appearance. As the name suggests, the formula of this type of product is watery and less solid if compared to oil-based formulas.

To get your desired results, you may have to apply many coats. Though on the positive side, it has fewer VOCs. However, it is still recommended to use them in a well-ventilated area. Also, avoid cleaning this product with any ammonia-based cleaning tools, as you can clean it with soapy water.

Oil-Based Polyurethane

These are the most preferred external polyurethanes; however, their usage is restricted in some states due to high VOC presence. Most people prefer oil-based polyurethane because it gives an appealing amber tinge to your wood and coats your surface effectively.

The disadvantage of such products is that they take a while to dry, which means you cannot use them for fast-paced projects, and you will also have to wait for coating in-between. To clean it, you can use mineral spirits.


Water-Based, Oil-Modified Polyurethane

 This is one of the ideal external polyurethanes for people who need qualities from both water and oil-based polyurethanes. It is not only fast drying but also gives an amber tinge to your surface, just like an oil-based product would. You can also clen it easily with soapy water, and despite being oil-modified, its VOC count is low.

Factors to Consider When Buying Exterior Polyurethanes

To make an informed decision about purchasing a brand of polyurethane, you must keep the following factors in mind:

How easy it is to use

Ease of use is a key factor if you’re a beginner. Moreover, you would need much less assistance to pull off easy projects

How long it takes to dry

If you’re working on a project that’s fast-paced and requires immediate results, go for polyurethane that dries quickly. If you’re working on a flexible project, a quick-drying polyurethane may not be necessary.

How flexible it is

Exterior polyurethanes should have the right amount of resin and oils so they can give your wooden surface a fine finish. It should also be resistant to any changes in weather conditions. However, recoat your painted surfaces every year, even if these additives are present in the mix. This suggestion could work well since adding a new coating layer means you hardly need to remove dirt and grease to prepare a surface. To remove dirt effectively, you can wipe your surface down with mineral spirits after sanding the surface.

How long-lasting it is

Even though it is an important factor, sometimes the long-lasting property alone is not as vital. You must choose a product that lasts long and gives your wooden structure the desired amount of protection. Long-lasting exterior polyurethanes save you from the hassle of refinishing and also save your time.

If it’s resistant to UV rays

Polyurethanes that give a clear finish may have some drawbacks. For instance, they make the wood visible and also unprotected as it gets exposed to the sun. Therefore, choosing a product based on the level of protection you’ll get from UV light is crucial, and achieving ideal protection by using a product that gives a clear finish is very tough.

Several polyurethane formulas have elements that can reflect UV light. One such component is titanium dioxide that can reflect sunlight. However, you must understand that no additive is 100% successful in blocking the sunlight away. If you keep adding more compounds to your polyurethane, it will end up appearing opaque and resembling paint.

Frequently Asked Questions

Is it necessary to seal the wood before applying polyurethane?

Some types do not necessarily require sealing. However, if you are required to seal, make sure that your sealer is compatible with varnish. Additionally, use a resin sealer that will seep well through the wood.

 What are the dangers of using polyurethane?

Some exterior polyurethanes have isocyanates. These substances can affect your lungs, and if left untreated, they can cause asthma and other breathing issues. Spending time in rooms with uncured polyurethane can also cause headaches, coughing, nausea, and vomiting.

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