Exterior polyurethane can enhance the natural beauty of the wood grain, providing a glossy or satin finish that’s aesthetically pleasing. However, choosing between the types of polyurethane is confusing and can make or break your DIY project.
If you don’t want to risk uneven or rough surfaces, our woodworking experts tested the best exterior polyurethanes to help you choose the right one for your needs.
Reviews of the Top Exterior Polyurethane Finishes
1. Minwax Helmsman Indoor/Outdoor Spar Urethane
This clear finish from Minwax, the Helmsman Spar Urethane, will keep your wood looking great and protected from the elements for years to come. Like an exterior coating, it acts as a barrier against water, making it ideal for kitchens, bars, and other exterior wooden surfaces prone to spills.
We like that it includes specific oils that allow the wood to grow and shrink with the changing seasons and contains UV absorbers to keep the wood’s surface from graying due to UV light.
Additionally, the Minwax Helmsman provided a clear and glossy finish that proved to be resistant to scratches and chemicals. It’s also easy to apply and dries quickly.
What We Like
- Ideal for interior and exterior surfaces
- Fast drying poly
- UV blockers
- Crystal clear finish
- Durable coating
What We Don't Like
- Messy cleaning
- It is not odorless
2. ZAR-34112 Ultra Fast Drying Exterior Polyurethane
The ZAR 34112 Ultra-Fast Drying Exterior Polyurethane is the latest high-quality offering from a well-known American wood stain manufacturer. Its unique recipe guarantees outstanding results, making it a good option for do-it-yourselfers and professionals wishing to bring out the wood’s natural color with a slight tint and a satin finish.
ZAR 34112 is an exterior polyurethane that not only protects wood surfaces brilliantly but also makes them look stunning due to its clear coatings.
The antioxidants and UV-resistant formula protect the exterior wood surfaces exposed to the sun’s rays. This external coating can also adhere to fiberglass and metal as an added benefit.
What We Like
- Marine grade and includes UV blockers
- Provides a smooth surface
- Easy to apply on exterior woods
- Weather-resistant
- Superior protection with satin finish
- Good shelf life
What We Don't Like
- A bit expensive
- Not ideal for beginners
3. Rust-Oleum Varathane 9341 Ultimate Oil-Based Spar Urethane
You can expect an extraordinarily long lifespan from the Rust-Oleum Varathane 9341 Ultimate. When it dries, it forms a firm surface and can hold up well because it is difficult to dent or destroy.
Unlike other versions, it is intended to be transparent and won’t age into a yellow hue. It contains UV rays blockers to prevent the graying of outdoor wooden surfaces. There will also be no mildew or mold to bother you, either.
It has the quickest drying time of the products we’ve looked at, as outdoor wood surfaces are dry to the touch in half an hour. After two hours, you can add another layer.
What We Like
- UV rays blocker
- Water-based exterior polyurethane
- It is mold and mildew resistant
- Crystal clear finish
- Quick drying oil-based formula
What We Don't Like
- Natural bristle brush required
- White hue when wet but turns back to normal if dried
4. 1 qt Deft DFT257 Clear Water Based Polyurethane
This interior and exterior polyurethane is water-based oil-modified and can be used for various purposes. The glass in your exterior doors, floors, windows, and tables can all be safely covered with this.
Water-based means it dries transparent, so you can apply another coat in two hours. You will not be concerned about your exterior surfaces fading to a dull gray because it is watertight and incorporates UV protection.
You’ll also like how straightforward it is to use. Brushes, swabs, and sprays are all proper tools you can use with them. And unlike other water-based treatments, you don’t need to use a penetrating resin sealer or any sealer before application with the Deft DFT257 Polyurethane.
What We Like
- Water-based oil-modified outdoor polyurethane
- Ideal for exterior and interior surfaces
- Dries clear on glass and wooden surfaces
- UV protection
- Quick drying
What We Don't Like
- Best for non-white colored surfaces
- Not sold in various sizes
5. TotalBoat Gleam Marine Spar Varnish
The TotalBoat Gleam Marine Spar Varnish comes in both satin and gloss finishes, promising to meet the needs of anyone who care about maintaining the aesthetic value of their exteriors.
You can apply the traditional maritime polyurethane paint to many different surfaces, and its phenolic resins and high-quality tung oil provide an attractive, translucent ambient final coat.
We like that it doesn’t require much effort to apply so that you may achieve a long-lasting and beautiful result. Moreover, it dries quickly and can be reapplied after only an hour. Best of all, you can apply up to three coats daily without sanding in between.
What We Like
- Easy application
- Ideal for various surfaces
- Available in satin and gloss wood varnish forms
- Best exterior polyurethane that withstands humidity
- It provides a durable wooden surface
What We Don't Like
- Solvents needed for cleanup
- Cleanup can be messy
6. MODERN MASTERS MCS90132 Clear Coat Matte
Modern Master MCS90132 is a water-based acrylic polyurethane that will not yellow with time for indoor and outdoor use. It provides a hard, transparent finish that dries rapidly and protects wood from moisture and wear.
In addition, It is reliable in preventing damage caused by oxidation, bird poop, and mold. UV absorbers and blockers are incorporated into the proprietary composition to protect the coating against premature deterioration.
It also has mildewcides built to prevent mildew growth, making hardwood surfaces last even longer. We found that it reduces gloss to a matte finish when applied to painted or prepared surfaces.
What We Like
- Highly-efficient outdoor polyurethane
- Dries fast
- It provides maximum durability
- Gloss to matte polyurethane finish
- Mold and mildew protection
What We Don't Like
- Pricey
- Consistency is a bit thick
What is Polyurethane?
Varnishes made with polyurethane are exceptionally hard because the resin molecules that make them up are linked in microscopic links or chains. The resulting finish will be more resistant to wear and tear as well as solvents and water than conventional disappears.
Oil-Based, Water-Based, or Both?
Even if improvements have been made in response to concerns over volatile organic compound (VOC) emissions, it’s still important to consider the following factors before purchasing oil-based or water-based poly:
Oil-Based Poly
A little amber tint of this poly can make your wooden surface more inviting. Applying just a few applications will give you a tough, long-lasting finish.
Unfortunately, it is unavailable in all areas of the country due to its higher VOC content than water-based alternatives. To remove oil from polyurethane, use mineral spirits.
Water-Based Poly
Water-based polyurethane starts milky but dries crystal clear, making it an excellent choice if you want to keep the natural color of your wood. You will need more applications than oil-based polyurethane, but the good news is that it dries rapidly despite its watery consistency.
Although the VOC content is lower than in an oil-based product, it is nevertheless important to apply it in a well-ventilated location.
Water-Based Oil-Modified Poly
This version dries to a golden hue. It dries quickly, can be used on any wood, emits few VOCs, and may be easily cleaned with water.
Exterior Polyurethane Buyer’s Guide
UV and Weather Resistance
Sunlight can damage wood, so avoid using a clear finish to show off the grain. Because of the complexity of UV blocking, most products use finely ground metallic compounds that are crystal clear to visible light but reflect UV rays.
Color
Contrary to the label claims, oil-based polyurethanes does not dry clear. Rather, they will dry with an amber tint, though the intensity varies by brand. The coat’s yellow color intensifies as it ages.
The water-based polyurethane dries transparent and keeps its clarity for the product’s life. When applied to white paint, however, it becomes an exception. If that happens, it turns yellow immediately, not in the warm amber way that oil-derived finishes are known for.
Ease of Application
A product’s ease of use is a major factor in your purchasing decision. It is a crucial consideration for first-time Do-It-Yourselfers. As you expect, your polyurethane is easier to apply. You can save money on a professional’s services.
Wood Type
In general, you may use any outdoor poly on any outside wood surface, but that’s not always the case. Therefore, you should pick an exterior polyurethane according to its intended application.
Flexibility
As the temperature and humidity outside fluctuate, wood contracts and expands. Thus, it is advisable to go for an exterior polyurethane with just the correct ratio of resins to oils to allow the layer to contract and expand with the wood. Before making a choice, it is important to determine how flexible the requirements are.
Durability
The product’s longevity is arguably the most crucial issue to think about. If you choose a long-lasting product, you won’t have to retouch the surface nearly as often, which is a significant cost saving.
Dry Time
Experts who must finish their tasks in a specific amount of time need to consider the drying time of the polyurethane. You should choose the best exterior finish with a quick drying time, so you can get more projects done in a day.
VOCs
Water-based polyurethanes win regarding odor and volatile organic compound (VOC) emissions. Manufacturers of common household items have gone to great efforts to cut back on volatile organic compounds (VOCs) because of the harm they cause.
It is one explanation for the widespread use of water-derived polyurethanes. Due to their chemical makeup, these polyurethanes emit less stench than their oil-derived counterparts.
Using a water-based finish is preferable, especially if you have to work in a space with individuals who are sensitive to smells, such as youngsters and dogs.
Always use a reliable respirator when working with oil-based exterior polyurethane to avoid inhaling toxic fumes and unpleasant odors. The good news is that once the poly dries, the VOCs are not dangerous anymore.
Do not apply exterior polyurethane inside your home or workshop to prevent unpleasant odors that are not easy to remove.
Cost
The high cost is the main drawback of water-based poly. Water-based topcoat spray cans are usually a couple of dollars more expensive. However, water-based Varathane is much more affordable than its oil-derived counterpart.
When costs are included, however, oil-based polyurethane emerges as the more economical option. The oil-based alternatives fill twice as much area as the water-based external polyurethane. It’s around 50% more expensive but accomplishes twice as much work.
Resistance to Stains
In many respects, water-based poly has outperformed its oil-based counterpart. And in some conditions, it may even be more resilient now. One area where it falls short, however, is stain resistance.
Rain can leave water-based polyurethane looking as milky as it did when you originally painted it. On the other hand, if you use Rust-Oleum, you can simply wipe it off, wait for it to dry, and it will be as good as new.
Coats Needed
How many coats of polyurethane you need to apply? Water-based polyurethane enhances wood grain; therefore, it requires more applications than oil-based polyurethane.
For this reason, a smooth finish may require as many as three or four coats. According to Rust-Oleum, the exterior water-based polyurethane needs at least four coats, while the oil-based kind needs at least three.
Finish and Sheen
The most prevalent polyurethane finishes are clear, gloss, and satin. You should check the product description to see what kind of finish it has, as this can affect the appearance of your wooden surfaces.
Extra Features
Since companies often provide extras, you won’t realize you need them until it’s too late.
The best exterior polyurethane should include extra features. The Zar outer poly, for instance, is infused with antioxidants. The fact that they offer it may make you feel like they have an advantage, and indeed, they do.
Varathane compounds are resistant to mildew and mold, which is certainly a remarkable quality since mold quickly spreads and is difficult to remove from wood and discolors the material.
How to Apply Polyurethane
Prepare the Wood Surface
All wood finishes require proper preparation before applying exterior polyurethane, meaning the surface must be clean and smooth. Start sanding the surface using 220-grit paper. Use wood grain filler before applying polyurethane to an open grain wood like oak, walnut, or ash.
To finish, use a vacuum or tack cloth to remove all the sanding dust from the wood surface. If you’re working with oil-based polyurethane, use a cloth drenched in mineral spirits, and if you’re working with water-based polyurethane, use cheesecloth drenched in denatured alcohol [1].
(Tip: Check out the best polyurethanes here if you’re working with wood countertops.)
Applying Oil-Based Poly
Mineral spirits can dilute oil-based polyurethane, which is usually unnecessary. Please refer to the manufacturer’s instructions for further information on this topic. Your wood’s surface may accumulate less finish if you thin it.
You can use either a foam or fine-bristle brush to apply polyurethane. Cheap paintbrushes can leave visible strokes on the surface. The foam brush is great for painting flat surfaces because it is inexpensive, disposable, and effective. Detail work is better with a paintbrush that has bristles.
Always use brush strokes perpendicular to the wood grain. Use lengthy, straight strokes to cover each section, as overlapping strokes will create bubbles. The last coat should not be overly thick.
When the first coat has dried completely per the manufacturer’s directions, lightly sand with 320-grit sandpaper in the direction of the wood grain, it’s important to be cautious while sanding the poly off, as doing so can damage the underlying wood.
Again, use a vacuum or tack cloth to remove all sanding dust. It’s time to put on the second coat.
As needed to achieve the desired polyurethane layer thickness and application quality can be carried out. You can apply a second coat to protect the wood, but if you live in humid areas and foot traffic, you should apply at least three coats.
After applying each application, the surface will feel smoother. Add paste wax after buffing it with fine-grade steel wool to achieve the desired gloss.
Applying Water-Based Poly
Water-based polyurethane will absorb oil stains, but the opposite is not true. Synthetic steel wool can rough up an area before applying water-based polyurethane over an oil stain.
Since water and oil cannot blend, this will stop the poly from beading out, like when water is poured over a waxed automobile.
Using water-based polyurethane is extremely close to oil-based polyurethane in terms of application. Apply your polyurethane in a thin coating using a foam pad, cloth, or paintbrush. Always make sure you paint in the direction of the grain, and never use too much finish, as this might cause the wood to rise.
You can apply a second layer within two hours after the initial layer of water-based polyurethane has dried. This method requires one but checks the manufacturer’s guidelines beforehand.
Water-based polyurethane requires a minimum of three coats for optimal results. A minimum of 4 applications is recommended for floors to get the necessary level of protection; apply more coats if required.
Spray vs Wipe-On Poly
Spraying or wiping on polyurethane to get a uniform layer is preferable because of its added thickness. Both techniques can apply a thin finish layer to inaccessible spots, but you must take care to avoid overloading the surface.
The spray approach is applied the same way as spray painting, whereas the wipe-on method calls for a dry, clean cloth without lint. Applying a polyurethane coating like a spray paint results in a flawless finish free of brush strokes; thus, many people choose to do it this way.
Interior vs Exterior Polyurethane: Key Differences
Waterproofing
Polyurethane applied on exterior wood surfaces outperforms interior polyurethane finish; it is also superior to paint and shellac as a wood finish because it chip or peel. Heavy rain, however, can damage polyurethane used indoors.
A few weeks of rain will allow water to permeate the wood, encouraging the growth of fungi, mildew, and mold growth. You can remove Mildew from the wood, but it’s a time-consuming and taxing procedure that you can avoid with the right finish.
Due to the excellent waterproofing properties of exterior polyurethanes, they are ideally suited for use in both outdoor settings and indoor bathrooms.
UV Protection
Polyurethane fails as a transparent coat in direct sunlight because it allows UV rays to penetrate the wood. Wood loses its natural beauty and turns gray when this happens.
Exterior polyurethanes must contain UV absorbers to protect outside wood, but interior polyurethanes rarely do.
Texture
Interior polyurethane dries hard and stays that way forever, but polyurethane used on the outside remains somewhat firm.
Outdoor wood contracts and expands as the weather changes, so exterior polyurethane must move in tandem with wood movement to prevent cracks. Therefore, external poly may not require as many coats and may not dry as hard
Other Extra Features
Other features of exterior polyurethane improve its suitability for severe weather. One of the things we look for is resistance to mildew and mold.
Because of this, even if water penetrates the wood and sits on the surface, as is inevitable, mildew will not form. Since there is rarely an issue with inside polyurethane, without significant water damage, that function is unnecessary.
FAQ
Can you recoat oil-based poly with water-based poly?
Recoating a water-based acrylic finish with oil-based polyurethane is not an issue as long as the old finish is cleaned and buffed thoroughly. Thus, good preparation is the best solution.
Can polyurethane make your wood waterproof?
Polyurethane does not make hardwoods waterproof, but it makes them water-resistant and protects them. The polyurethane will prevent the wood from absorbing any further moisture and repel any water that gets through.
By creating a barrier, polyurethane preserves the natural beauty and integrity of the wood while enhancing its resistance to water damage.
Is sealing wood needed before the poly application?
Most polyurethanes do not require you to seal the surface beforehand, but if it does, choose one that is suitable. Use a permeating resin sealer to finish off the wood, then add polyurethane for a smoother finish.
Can you apply interior poly over exterior polyurethane?
There is no requirement to apply interior polyurethane over exterior polyurethane directly because resin, a flattening agent used in external poly, helps lower shine while also soaking up UV light. Remove the existing polyurethane, then put a new coat of your chosen poly.
Can you apply marine polyurethane on hardwood floors?
Indoor application of marine polyurethane may not yield the greatest results. It was built with the outdoors in mind and can handle the elements. Instead, look for a polyurethane coating designed for indoor use.
Is polyurethane toxic?
The isocyanates in polyurethane are hazardous and have been linked to lung damage. However, those made with water are less hazardous. Refer to the product’s instructions for further information. The best preventative measure is always to use safety equipment.
Our Top Pick For an Exterior Polyurethane: Minwax Helmsman Indoor/Outdoor Spar Urethane
Our unanimous choice for best exterior polyurethane is the Minwax Helmsman. It gives a durable finish and is resistant to water, sun, and temperature changes.
It is available in gloss, semi-gloss, and satin finishes. We also like that it can be applied using a brush, roller, or sprayer and is dry to the touch within 2-3 hours.
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