If you’ve ever tried using interior polyurethane on exterior wood only to watch it epically fail, welcome to the club! Sure, it looked great at first until it rained or snowed, and you had to strip it and start all over.
That is why it is important not to use just any exterior polyurethane but to find the best exterior polyurethane, and that’s what we’ve done.
Check out our review and guide below to help you avoid the mistakes many of us have made in the past.
Best Exterior Polyurethane
- RUST-OLEUM Ultimate Oil-Based Spar Urethane – (Editor’s Pick)
- Minwax Helmsman Indoor/Outdoor Spar Urethane – (Best Exterior Poly for Small Projects)
- RUST-OLEUM Ultimate Water-Based Spar Urethane – (Best Exterior Water-based Polyurethane)
- Deft Interior Exterior Water-Based Polyurethane Finish Gloss, Quart – (Best Interior/Exterior polyurethane)
- ZAR Exterior Oil-Based Polyurethane – (Best Multipurpose Exterior Polyurethane)
The Best Exterior Polyurethane Reviews (Updated List)
I’ve carefully considered the polyurethanes on the market. Using real-world experiences and advice from the other woodworking experts, I’ve pulled together a list of the best exterior polyurethanes. Here are my top five choices.
1. Editor’s Pick–RUST-OLEUM Ultimate Oil-Based Spar Urethane
- Protects outdoor wood surfaces such as furniture, fences, railings, trim and more
- Oil based formula provides maximum durability and allows for a more even finish
- Dries to the touch in 2 hours with coverage up to 190 sq. ft., recoat after 8 hours
- Weather and UV resistant formula protects the surface from graying and sun damage
- Satin finish provides a classic and natural look
First on our list is a brand that has been at the forefront of woodworking innovation for decades, and their exterior spar urethane does not disappoint.
The Varathane Ultimate spar urethane can be used on furniture, fences, railings, window frames, and a host of other outdoor woodworks.
This oil-based product is very durable, and from the language, Rust-Oleum uses to describe it, it may be even more durable than the water-based alternative and potentially give a smoother finish.
You also get top-of-the-line weather protection, and it is also ultraviolet (UV) resistant. This means the wood won’t absorb water, and neither will it gray or break down due to UV rays, which tends to happen with clear coats.
One thing that sets this apart from cheap imitations is that it has a unique formula that allows it to expand and contract with the wood. It also offers protection from mold and mildew.
As this is an oil-based product, it does not dry as quickly as water-based alternatives. However, you can apply the next coat in 8 hours, which is pretty fast for an oil-based urethane.
The one major knock against this is that it is more expensive than most other products on our list. However, it has a large coverage area of 190 sq. ft per quart.
- Has UV protection
- Expands and contracts with wooden surface
- Offers mold and mildew protection
- Fast drying for an oil-based product
- Quite expensive
2. Best for Small Projects–Minwax Helmsman Spar Urethane
- Recommended Uses: furniture, woodwork, molding, cabinets, doors, paneling, accessories
- Application Tool: natural bristle brush
- Dry Time: 24 hours before normal use
- Cleanup: mineral spirits or paint thinner following manufacturer's safety instructions
- Contains UV blockers to reduce the sun's graying and fading effects
Next up, we have an outstanding interior and exterior spar urethane that boasts similar characteristics to the Varathane Ultimate. As you would expect from an exterior finish, it provides a protective barrier against rain and moisture, making it perfect for use in bathrooms, bars, and other surfaces often covered in liquid.
It also has UV absorbers to prevent the wooden surface from graying, and it has special oils that allow it to expand and contract as seasons change.
When it comes to application, this is even quicker than the Varathane. When using a natural bristle brush, you can apply another coat in 4 to 6 hours. When using a sprayer, you can apply subsequent coats in 1.5 hours.
Even though this is an interior/exterior product, it is not meant for large surfaces such as decks, fences, or indoor flooring. It also shouldn’t be used on white-painted surfaces.
Amid thousands of positive reviews, one issue some users have noted is that it yellows. Minwax says this product dries clear, but it is important to note that ‘dries clear’ is usually the language manufacturers use for oil-based finishes.
Water-based polyurethanes that don’t yellow at all (unless applied on white paint) are said to dry ‘very clear.’ So, if the yellowing is a problem, you might want to check out the following product.
- Suitable for interior and exterior use
- Easy to apply
- Fast drying time
- Has UV absorbers
- It can’t be used on fences and decks
- Has a strong odor
3. Best Exterior Water-based Polyurethane–RUST-OLEUM
We are back to Rust-Oleum, but this time, we are admiring this water-based iteration of their spar urethane. This provides complete weather resistance from rain to humidity, temperature changes, and sunlight like the oil-based option.
UV rays blockers in this product will protect your outdoor woodworks from graying. You also get protection from mold and mildew.
As this is a water-based product, it does not yellow either now or in the future. It also has a low odor, so you won’t need a respirator to apply this.
Of the products reviewed so far, this has the fastest drying time. Within half an hour, your doors, window frames, or fence will be dry to the touch. You can apply another coat after two hours.
To get maximum durability from this product, you will need to apply at least four coats. This gives it the lowest coverage area so far, of only 87 sq. ft per quart, which is less than half the capacity of the oil-based alternative.
Once you are done, you can clean your tools easily with just soap and water. The one major drawback is that this product turns milky when it rains. However, as soon as you wipe it down and leave it to dry, it looks just as good as new.
- Fast drying
- Protection from UV rays and light
- Mold and mildew protection
- Does not have a yellow tint
- It is quite expensive per sq. ft
- May turn milky when wet
4. Best Interior/Exterior polyurethane–Deft Finish Gloss
- Interior/Exterior Multi Use Focus
- Greater Durability Than Oil Based Poly
- 2 Hour Recoat
- Water based polyurethane provides ideal protection for interior and exterior wood surfaces
- A 100-Percent urethane water-based clear protective top coat, formulated with the latest water-based oil modified urethane technology
One of the best ways to save money on woodworking projects is to buy two-in-one products, just like this interior exterior water-based oil-modified polyurethane. Oh my, that’s a mouthful!
But is it all words and no action, or does this product meet expectations? This multipurpose polyurethane from Deft is the real deal! It can adequately protect your furniture, doors, floors, windows, window frames, and outdoor tables, to name a few.
As it is water-based, it dries clear, and you can apply the next coat in 2 hours. Besides being waterproof, it also contains UV rays protection, so no need to worry about your furniture turning gray over time.
Another thing you’ll appreciate about this is that it is easy to apply. You can use a brush, a pad, or spray. And unlike many water-based finishes, you also don’t need to use a sanding sealer before applying.
Amid all the great reviews we saw, which included favorable comparisons to other brands on this list, was a comment on yellowing. When applied on white paint, it will absolutely yellow.
However, this is common with all water-based polyurethanes. Nearly every manufacturer has a disclaimer about using polyurethane on white paint, so this is not a stain against Deft polyurethane.
- Fast drying
- Dries clear
- Easy to apply
- Offers UV protection
- It yellows on white paint
- Only sold in 1-quart sizes
5. Best Multipurpose Exterior Polyurethane–ZAR ZAR 34112
- Provides superior protection on exterior wood surfaces
- Outperforms other exterior clear finishes by 2-1
Finally, we come to another product that delivers consistently exceptional results. Zar exterior oil-based polyurethane offers a marine-grade finish to patio furniture, fences, gables, doors, and window frames. It is excellent for a wide range of external woodworks that need a clear coating.
Like the other polyurethanes on our list, this has UV absorbers, but it also throws in antioxidants. So this will not only protect your wood from graying but also keep it from losing its color and strength over time.
Of all the oil-based exterior polyurethanes on our list, this one has the fastest drying time. You can apply a second coat in just two hours, and it is completely dry in 4-6 hours. Using either a natural bristle brush or a spray, you need to apply at least three coats.
As a bonus, this exterior finish can also be applied to metal and fiberglass.
In terms of coverage, each quart will handle between 125 – 150 sq. ft. Even though it is meant for exterior use, many reviewers have used it for indoor projects with admirable results.
- It dries quickly
- It contains UV absorbers and antioxidants
- Easy to apply
- No protection from mold and mildew
What is the Difference Between Interior and Exterior Polyurethane?
Suppose you have read our reviews of the best water-based and oil-based polyurethanes for hardwood floors, you may have noticed some terminologies are missing or added.
That is because interior and exterior polyurethanes do the same thing but in different ways. some of the differences are:
Interior polyurethane dries hard and remains that way forever, while exterior polyurethane maintains a bit of rigidity.
Changes in temperature, moisture, and humidity cause outdoor wood to shrink and expand. Exterior polyurethane needs to be able to shrink and expand with the wood. As a result, exterior poly does not dry as hard and may not need as many coats.
2. UV protection
As a clear coat in the sun, polyurethane cannot prevent uv rays from penetrating the wooden surface. When this happens, the wood becomes gray and dull.
To protect outdoor wood, every exterior polyurethane must have UV absorbers, while it is not required and even rare for interior polyurethane.
Polyurethane is a great coat for wood because it is waterproof, unlike paint and shellac. However, interior polyurethane cannot handle heavy rain. After a few weeks of rain, the water will seep through the wood, which will cause mold, mildew, and wood fungi to grow.
Even though it is possible to get rid of mildew on wood, it is a long and draining process and easily preventable by using the correct finish.
Exterior polyurethane has superb waterproofing capabilities, making it great for the outdoors and bathrooms.
3. Other special features
Exterior polyurethane also has other attributes that make it better suited for harsh weather. One such feature on our list is mold and mildew resistance.
If water manages to get through to the surface of the wood, which will happen eventually, at least there will be no mildew. Interior polyurethane does not need that feature because that is almost never a problem unless there is serious water damage.
While it may be possible to use exterior polyurethane indoors, you should never use interior polyurethane outdoors.
Should I use Water-Based or Oil-Based Exterior Polyurethane?
Now that we have established that you can only use exterior polyurethane outdoors, it is time to look at how to choose the right one. There are many factors to consider when looking for the best exterior polyurethane, and we will get to that later, but this one deserves its own space.
The battle between water-based and oil-based polyurethane has plagued man from the beginning of time, or it at least feels like it.
To give you a fair assessment, we have to analyze how each one performs in different categories.
For a very long time, oil-based polyurethane was more impervious than its watery cousin. Nevertheless, things began to change a few years ago, and now, water-based polyurethanes are just as durable, if not more durable.
However, when it comes to exterior polyurethane, oil-based polyurethane is still the undisputed champion. Exterior oil-based polys offer longer-lasting protection, something Rust-Oleum essentially admitted in their own descriptions.
Even though great strides have been made to improve the durability of water-based poly for floors, the same hasn’t happened in exterior polyurethanes yet.
2. Drying Times
The competition isn’t even close for this one. Water-based polyurethane will always dry quicker than oil-based polyurethane, just as water dries faster and evaporates quicker than oil.
Of the products listed above, the water-based Varathane and the Deft are dry and ready for a recoat in two hours. On the other hand, the quickest drying oil-based polyurethanes, which are the Minwax and the Zar, need between 4-6 hours before applying a second coat, which is fast for an oil-based finish.
3. Odor and Volatile Organic Compounds (VOCs)
This is another slam dunk for water-based polyurethanes for both odors and VOC emissions. Given how harmful VOCs are, manufacturers of household products have gone to extreme lengths to reduce them.
That is one reason why water-based polyurethanes are more common. Given the chemical makeup of this type of polyurethane, they also don’t smell as much as oil-based polyurethanes.
Some water-based polys are almost odorless, like the Varathane Ultimate Spar Urethane.
Why is odor a factor? Some people find it repulsive, and if you are working around children and pets, it is much safer to use a water-based finish.
When using oil-based exterior polyurethane, it is important to wear a respirator at all times to protect you from the odor and the VOCs. The good thing is the VOCs are no longer harmful when the poly dries.
- Oil-based polyurethanes don’t dry clear, despite what you might read on the can. Instead, they dry with a bit of an amber hue, though some brands are more amber than others. As the coat gets older, it becomes even more yellow.
- Water-based polyurethane dries clear and remains clear for the duration of the product. The only exception is when it is put on white paint. In which case, it immediately turns yellow and not the type of amber glow people appreciate with oil-based finishes.
So, who wins this round?
It is entirely up to you. At the end of the day, you get to choose how you want your wood to look, whether you want it to maintain its color or to appear a little darker.
That is why you also get to decide on what type of stain to use. Just me like, you could decide that you will use water-based polyurethane for some finishes, and oil-based for others, depending on how you feel.
So, don’t be swayed by reviews that complain about finishes yellowing. Just follow the instructions, don’t apply polyurethane over white paint, and you’ll be fine.
The major knock against water-based polyurethane is the price. Cans of water-based topcoats are typically a few dollars more. The only exception, in this case, is with the water-based Varathane, which is significantly cheaper than the oil-based alternative.
However, when you look at the figures, the oil-based polyurethane ends up cheaper. In this case, the oil-based options cover more than twice the square footage of the water-based exterior polyurethane. So while it costs roughly fifty percent more, it does twice the job.
So, it might be more expensive up front, but not when applied. Some other water-based polys are more expensive and still cover less wood.
That being said, water-based polyurethane makes up for this in other ways. If you choose a product that doesn’t need sanding, you’ll save money here. You also get to finish the task significantly quicker, meaning you can move on to the next task.
So, even though water-based polyurethane is cheaper, it could make you more money when you have a backlog of work to do.
6. Stain Resistance
Water-based polyurethane has exceeded oil-based poly in many ways. Now, it might even be more durable in some settings. But the one thing it can’t seem to get right is stain resistance.
When rain pours on water-based polyurethane, it can appear milky, just like how it looks when you first apply it. However, in the case of the Rust-Oleum, you can just wipe this off and let it dry, and it will be back to normal.
You can expect the same thing from superior brands. However, cheaper brands might turn milky and remain milky.
7. Number of Coats
In a nutshell, water-based polyurethane needs more coats than oil-based polyurethane because it raises the grain of the wood. As a result, you often need three or four coats to get a smooth finish. Rust-Oleum recommends at least four coats for the water-based exterior polyurethane and at least three for the oil-based. Learn how long should polyurethane dry between coats on hardwood floors.
How to Choose the Best Exterior Polyurethane
So, how is that tally looking? Which of the two polyurethanes are you leaning towards right now? Actually, hold that thought.
Before you make that decision, here are a few other things to consider.
1. The Wood you Need to Apply it on.
Not every product we’ve listed is suitable for every type of exterior wood surface. Therefore, it is important to select an exterior polyurethane based on where you want to use it.
All of the options we provided can be used on doors, window frames, and outdoor furniture. However, the Minwax cannot be used on fences or other large surfaces that might be difficult to manage.
So, if you want to use the exterior polyurethane on a fence, it won’t matter that the Minwax is oil-based; what matters is where you want to apply it.
2. UV Absorption and Weather Resistance
This is a tricky one to decide because all of them on our list boast UV protection and superior weather resistance. It is pretty difficult to decide which one does it best, so we can leave this one as a tie.
3. Ease of Application
To get a smooth and blemish-free finish, you need to know how to apply polyurethane the right way. Whichever product you buy will be relatively easy to apply. What sets them apart is if you need to sand between coats, how many coats you need, and the tools you can use.
The water-based Varathane requires at least four coats, and you also need to sand between coats. However, it dries quickly, so you can apply three coats in one day.
The Deft interior/exterior polyurethane is probably the easiest to apply, given that you can use a brush, a pad, or spray. Unfortunately, most of the others only give two application methods.
Not only that, but it is also self-priming, and you don’t need a sealer. You can also wash your tools easily with soap and water, which is an important part of the application process.
Polyurethanes typically come in four sheen or luster options: matte or flat, satin, semi-gloss, and gloss or high-gloss. The glossier it is, the more light it reflects, and sadly, the more scratches and dents it reveals.
Only the Minwax is readily available in two different sheens – gloss and satin. The rest are either satin or gloss.
Is that a deal-breaker? Not quite. This is a matter of choice, so there is no right or wrong answer to this. You also need to be mindful that when you don’t stir the products during the application, they may appear glossier than what is written on the tin.
5. Other Features
Yes, this is a bit vague, but only because manufacturers like to throw in things you never knew you needed until you see them.
For example, the Zar exterior poly has antioxidants. They are the only ones that offer it, and it might make you feel like that gives them an edge, and it does.
However, the Varathane products offer mold and mildew resistance. Now, that’s an impressive feature. Not only does mold discolor wood, but it also spreads quickly, and it’s hard to remove.
Final Thoughts on the Best Exterior Polyurethane
And so, we come to my least favorite part of the review because these are all so good. However, the best exterior polyurethane is the Rust-Oleum 9341 Ultimate Spar Urethane Oil Based. Even though it has the longest drying time, it is very durable, offers exceptional protection from the elements, and is mold and mildew resistant.
The water-based alternative is a worthy contender, but its small coverage area is a problem. The Deft exterior/interior polyurethane had a chance to take the top spot, but it doesn’t have any extra features to push it over the top.
Let us know what you think of our list, or jump straight to our review of the best brush for polyurethane.