A nice, thick coat of polyurethane is one of the best things you can do to improve the appearance and longevity of any wooden item. With one cheap and relatively easy step, you create a pleasing shine while protecting the item from moisture. In this article, we will concentrate on exterior polyurethanes. These coatings have to be a little more durable than those that are intended for interior use. They have to stand up to the harshest abuse that nature can inflict, and they have to do it for a long time.
With that in mind, let’s look at our top five picks for the best exterior polyurethanes.
Best Exterior Polyurethanes in April, 2024
| Polyurethane | Coverage (quart) | Recoat dry (hours) | Sheen | ||
|---|---|---|---|---|---|
| 1 | Minwax Helmsman Urethane Editor's Choice | 125 sq ft | 4 | gloss, semi-gloss, satin | Check Price |
| 2 | Rust-Oleum Urethane Oil Based | up to 190 sq ft | 8 | gloss, semi-gloss, satin | Check Price |
| 3 | Rust-Oleum Urethane Water Based | up to 87 sq ft | 2 | gloss, semi-gloss, satin | Check Price |
| 4 | ZAR Exterior Oil Based Poly | 150 sq ft | 2 | satin | Check Price |
| 5 | ZAR Exterior Water Based Poly | 125-150 sq ft | 2 | gloss | Check Price |
1. Minwax Helmsman Indoor/Outdoor Spar Urethane – Best Polyurethane for Exterior Wood
This is a clear coating meant to be used anywhere, whether indoors or outdoors, and we can see that it was formulated for that purpose. First of all, this is one of one gallon-size can that we will examine today, and these gallon-size cans represent a significantly better value than the quart-size cans. When you buy your clear coat by the gallon, you are paying a lot less per quart.
Meant For Hard Use
This finish is meant to deal with the worst of the outdoors. First of all, they included a strong dose of UV blockers to keep this stuff from yellowing after it has sat in the sun for a while. This will also help to keep it from peeling and flaking over time. This coating also apparently contains some special oils that help it to deal with temperature extremes more easily. These oils will allow the coating to expand and contract the same way that wood and metal do.
Dries Very Quick
Despite all these durability-enhancing additives, this coating still maintains a crystal clear finish. It won’t change the color of the paint underneath, but it will give it a lovely shine. I also like the fact that this clear coat dries pretty quickly. This means less time between coats and less project time overall.
At the same time, this low drying time can be a problem at certain times. If you are doing the kind of project that requires minor corrections, you might be out of luck. This coating doesn’t give you much time for corrections. You will ruin the finish if you put a brush to this coating after it has begun to harden. That will force you to sand it down and start over.
Kind Of Watery
The consistency of this stuff is thin, and so it tends to soak into certain surfaces. Soft, porous wood and foam are particularly problematic in this regard. As a result, it will usually take more coats to achieve the same results with this product, reducing its cost-effectiveness by a slight margin.
- Good value
- Contains UV blockers
- Meant for expansion and contraction
- Crystal clear
- Dries fairly quick
- Doesn’t give much working time
- Might be a little too thin
2. RUST-OLEUM Ultimate Oil-Based Spar Urethane – Top Poly for The Money
This is the second of our gallon-sized entries, and it is pretty cheap. In terms of price per quart, this one beats the others by a significant margin. Rust-Oleum is one of the more prominent names in the business, so it’s impressive that this paint is so cheap. As such, it represents one of the best values on the list.
Resists UV Light
Like any good outdoor polyurethane, this one is meant to resist UV degradation. Many people might be surprised at just how much the sun can degrade a finish. It’s good to know that this one is formulated to resist such problems, but it might not have even been necessary to add those extra elements. Because this is an oil-based finish, it is less susceptible to UV damage anyway.
Good Outdoor Performance
Like the previous choice, this one is well-suited for the rigors of outdoor use. Apart from its resistance to the sun, it also includes ingredients that help it resist mold and mildew. For exterior surfaces, this is a great advantage. Anyone who has ever had to remove mold from the side of their home will attest to the fact that it’s an unpleasant job.
Because it’s an oil-based finish, this product is not susceptible to water damage at all. It resists rain, fog, humidity, and pretty much any other kind of moisture. This is because oils are naturally hydrophobic. That’s a fancy way of saying that they don’t like water, and water doesn’t like them either.
The Downsides
I do see a few minor issues with this product, of course. First of all, the advertising says that it will darken to a “rich, golden glow” over time. When I read this, it made me a little concerned. This clear coat may not remain clear forever and may take on a yellowish hue. For some projects, like antique furniture, this might not be a problem.
I also can’t help but notice that this stuff doesn’t dry very quickly. It takes up to eight hours between each coating, and that will probably create some delays. Still, it’s hard to complain about drying time at such a reasonable price.
- Best value on our list
- Formulated to resist mold and mildew
- Exceptionally shiny
- Flexible and waterproof
- Resists UV rays
- Might change color over time
- Requires 8 hours between re-coats
3. RUST-OLEUM Ultimate Water-Based Spar Urethane – The Watery Cousin
This one is very similar to choice number two, right down to being manufactured by the same company. However, this one differs significantly in the fact that it’s water-based. Thus, we have two versions of the same product here.
Clear and Hard
This coating does provide an exceptionally durable finish. It dries hard and creates a rigid surface. This surface is pretty hard to dent or damage, so it seems like it will hold up well over time. Unlike its oil-based cousin, this one is meant to be clear. Thus, it should avoid the tendency to yellow as it ages.
Very Time-Effective
Unlike its oil-based cousin, this coating is rapid and easy to use. It only requires 30 minutes to dry and can be re-coated in about two hours. That is leaps and bounds ahead of the other version. Overall, you couldn’t ask for a quicker working product than this.
Some Complaints
Although this item gets excellent reviews overall, some complaints caught our attention. At least three reviewers said that this coating would take on a white, milky color when it rains or otherwise gets wet. They say it will return to normal after drying out again, but this is still a severe potential flaw. Because most buyers, including me, did not complain about this factor, I believe that it was either a defective batch or a case of user error.
Some others have remarked that this clear coat is too thick and thus challenging to spread on a surface without leaving streaks and other marks.
- Very hard finish
- Less odor
- Easier cleanup
- Non-yellowing
- Quick-dry time
- Easy to put streaks in the surface
- Some say it turns white when wet
4. ZAR Exterior Oil-Based Polyurethane – Rich Shine Exterior Urethane
This is a satin finish. It imparts a slight tint to the surface on which it is used. This slight tint can actually make a big difference when finishing certain kinds of wood. Any type of wood that has a reddish tone will pop out by this finish, as it will bring out the natural colors more fully.
Beauty And Durability
I like this finish because it offers a great mix of durability and beauty. Even by the standards of an oil-based finish, this one produces a very high shine. There is just no comparison between a coating like this and the relatively dull finish provided by a water-based coating. It gives a look that is both classic and modern at the same time.
Apart from its nice looks, this product is also very tough. It is hard enough to resist damage, yet flexible enough to resist weathering. It has proprietary ingredients to help it resist UV damage, and it even has antioxidants. Because most clear coat discoloration is caused by oxidation, an antioxidant is a natural choice if you want to prevent yellowing and staining.
May Not Be Consistent
Some customers have complained about the consistency of this product. Some say it was too thin, while others say it was too thick. Others say it was a mix of the two. Either way, there is a lot of consistency in these reviews. What I read here points to a problem with consistent performance. I would guess that this product doesn’t have a particularly long shelf life.
- Satin finish works well with some woods
- Deep, rich shine
- Meant for beauty and durability
- Very resistant to UV light
- Antioxidants to resist yellowing
- Some complaints about the uneven thickness
- Short shelf life
5. ZAR Exterior Water-Based Polyurethane – Marine Grade Urethane
This is one of the most expensive coatings on the list, but it’s not that far ahead of the other two quart-size cans. As such, its price isn’t a huge downfall. Still, this one gives extreme water resistance and a lot of other perks.
Good Enough For A Boat
This is the only marine polyurethane on my list, which means it is a very water-resistant coating. All polyurethane coatings are water-resistant due to the nature of the material, but this one is obviously a little bit more so. For areas that see a lot of rain, or areas near the waterside, this finish is an ideal choice. Of course, I should mention that it is recommended to use this coating above the waterline. Thus, it’s a waterproof coating but not suitable for underwater usage.
Not Harsh Or Messy
This is a water-based coating, and it seems to be a little thinner than most. When you open up the can, its fumes are not too bad. Cleanup is extremely easy and requires no special chemicals. Brushes can be rinsed with water and allowed to air-dry.
Made For The Outdoors
I have already talked about UV protection and antioxidants, as well as some of the other additives that separate exterior polyurethanes from interior ones. This product seems to contain all of those important additives, so I will simply say that this one should hold up to the weather very well indeed.
A Little Goes A Long Way
Some reviewers have remarked on the good coverage offered by this product. This is probably due to its thin consistency and its extra waterproofing. A more durable coating allows you to use thinner coats, which makes the product last a little longer.
- Suitable for marine use
- Easy cleanup
- Contains antioxidants
- Very good coverage
- Long shelf life
- Discolors slightly as it dries
- Most expensive on our list
- Prone to bubbling
Conclusion
After putting in the time and effort to create an attractive paint job, it would be incredibly dumb to ruin all of that work with a substandard polyurethane finish. That’s why you need to choose carefully and avoid inferior products. While there isn’t a whole lot of variation between these products on the list, you can see a lot of differences on closer inspection. Overall, I would advise you to look at six factors: durability, beauty, drying time, value, rate of defects, and coverage. By following my instructions, you should have no trouble obtaining the results you want.
Hi William! I have put 2 coats of Rustoleum Marine Spar Varnish on an unfinished interior bathroom pocket door (lightly sanding between each coat). I applied the 1st coat with a sponge brush and the 2nd coat with a soft paint brush since some areas on the door have a skinned appearance where the wood and varnish doesn’t seem to be bonding. The brushed on varnish had to be applied thick to cover the skinned looking spots. My problem is, I’m pressed for time. I have a contractor that needs to install the door in a few days….so I was wondering if I can put a water based polyurethane over the marine spar varnish to smooth it better, as well as harden it?
Hi, Linda. Short answer? No.
You’ll be adding to the problem and potentially giving yourself a world of grief. The only way to speed up the drying time of either spar varnish or polyurethane is to increase the airflow across it, warm it up slightly, and reduce the humidity around it.
If that sounds like a fan heater to you, you’re right. Don’t overheat it, though. Ten degrees temperature change will dramatically increase the drying time, but too much more might cause problems requiring you to strip it off and restart it. Good luck!
Hello Will
We recently cut down a large tree in our yard and left a 10 feet stump that I’ve used to hang plants. What is the best product to use to cure or preserve the wood so that it doesn’t rot or become infested with termites?
Your expert opinion is truly appreciated.
Hello, Claudene.
It sounds as though the stump is still in the ground and you wish to preserve it.
However, be aware that while whatever you do will slow the rot, but it will ultimately rot given that the roots are still in the soil and wicking moisture up into the stump.
I’m not sure if you have the bark on or off – if the bark is off, I’d be cleaning the stump, getting the surface as dry as possible, possibly sanding the exposed surfaces with 80-grit sandpaper, and then applying a matte oil-based polyurethane or even better, a spar varnish (here’s a good one: https://geni.us/v44Rv7e).
You can use a wood stabilizer, but that costs a bit and given the stump will still rot, you’ll be wasting money. If the bark is on, it gets even harder as while you might apply a sealer or polyurethane to the bark, the moisture will get in behind the bark and the stump will still rot. What ever you do will delay the inevitable by a year or two.
Hi William!
Thank you so much for your blog. I’m new to this and was wondering if you could help me.
We have an old home (100 year old redwood inside!) with hardwood flooring on the front porch. It is covered but gets a little sun and some rain (very little, we live in San Diego).
The porch flooring had a varnish on it, but we are sanding it down to bring out the natural wood again and want to cover it with a clear sealant. I’ve been looking at clear sealants like Superdeck, TWP, or marine poly/urethane. What do you recommend?
Thank you!!
Emily
Hello Emily,
If you don’t want to use varnish, I suggest you use this sealer by Seal-Once.
It is Water-based, low VOC, non-toxic, safe for people, pets, and plants; specially formulated to be applied around and over fresh or saltwater.
It penetrates deep into wood fibers, coating them like an oil-based sealer without the harmful chemicals or side effects. It enhances, stabilizes, and protects wood by creating a flexible, breathable barrier.