Spar Urethane Vs Varnish | The Differences You Must Know

Fact Checked By James A Rockey | Post Updated On: December 4, 2022
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The difference between spar varnish and spar urethane is that the former is a natural product, while the latter is synthetic. The two products are water-based but offer different qualities for your woodworking project.

Key Takeaways

  • Spar varnish is a hand-rubbed finish that provides a durable, protective layer of oil and wax
  • Spar Varnish can be applied to any surface including wood, metal, and concrete
  • Spar Urethane is an industrial-grade paint with the same durability but without a hand-rubbed look
  • If you are using Spar Urethane then you have to wait at least 24 hours after the final coat has been applied for the product to cure completely

What Is Spar Varnish And Why Is It Used?

Spar varnish is a wood-finishing varnish. It was originally used for coating the spars of sailing ships. But it is now used for the finishing of various other word products. 

TotalBoat - 409314 Gleam Marine Spar Varnish, Gloss and Satin Polyurethane...
  • CLASSIC MARINE VARNISH contains premium tung oil, phenolic resins and UV blockers for a beautiful transparent amber finish on all types of interior and exterior wood on boats, strip canoes, kayaks, outdoor wooden bar tops, garage doors, furniture and more
  • DURABLE URETHANE SPAR VARNISH with maximum UV resistance; it remains flexible after curing, and won't peel or crack when the wood expands and contracts with seasonal humidity and temperature changes
  • EASY TO APPLY BY BRUSHING, ROLLING OR SPRAYING: For a high gloss finish, apply 4-6 coats of Gleam Gloss; for a sleek satin finish, build with coats of Gleam Gloss varnish and use Gleam Satin for the final coats; Application Temp: 45-105F, 0-85% RH
  • SELF-LEVELING FINISH DRIES FAST: Recoat in 1 hr. @ 72°F; apply up to 3 coats in 1 day; if desired, thin 5-10% with TotalBoat Special Brushing Thinner 100 (brush/roller application) or 10-20% with TotalBoat Spray Thinner 101 (spray application)
  • AVAILABLE IN GLOSS OR SATIN (low-sheen), in Pint, Quart and Gallon sizes; Coverage: 360-400 sq ft/gallon; Thinner: TotalBoat Special Brushing Thinner 100 (brushing/rolling); TotalBoat Spray Thinner 101 (spraying)

Varnish has many uses apart from providing a finishing. It protects the wood from harmful ultraviolet rays and it also protects the wood. Apart from that, it protects the wood from water which is why it was originally used on wooden boats, etc. Varnish provides the wood with a rustic outlook to give an authentic look. 

What Is Spar Urethane And Why Is It Used?

Spar urethane is actually a spar varnish that uses plastic urethane as its resin. It is commonly used for exterior woodwork but because it has high resin content, it gives a yellow hue that cannot be used inside a house. But it has been found that it is a great finishing for woodwork that are more prone to water content. Such as bar tops, etc. 

Minwax Helmsman Water Based Spar Urethane, Quart, Gloss
  • PROTECTIVE CLEAR FINISH – Minwax Helmsman Water Based Spar Urethane is a crystal clear wood finish that is specially formulated to protect against nature’s toughest conditions.
  • EFFECTIVE YEAR ROUND – This wood varnish forms a protective barrier against rain and moisture to protect your projects and keep them looking their best. Special oils allow the finish to expand & contract with the wood as seasons and temperatures change.
  • VERSATILE – Ideal for use on doors, windows, trim, bathroom cabinets, bar tops, kitchen countertops, outdoor furniture and more. It’s a versatile water-based spar urethane that dries quickly and cleans up easily with warm water.
  • GLOSS FINISH – Give your wood projects a sleek finish with this gloss clear varnish. It not only protects the natural beauty of the wood, but offers a shiny, sleek sheen for a modern look. It’s ideal for use over light colored woods and stains.
  • A BRAND YOU CAN TRUST – Minwax is America’s leading brand of wood finishing and wood care products. Since 1904, we have been inspiring consumers to Keep on Finishing. We offer consumers a complete line of products to meet every wood finishing need.
  • Spar urethane
  • Specially formulated protective clear finish for exterior or interior wood that is exposed to sunlight, water or temperature changes
  • Contains UV blockers to reduce the sun's graying and fading effects
  • Forms a protective barrier against rain and moisture
  • Special oils allow the finish to expand and contract with the wood as seasons and temperature changes

One might think that both spar varnish and spar urethane are similar products or that there are no differences. But there are some slight differences between the two.

What Is The Difference Between These Two?

While both spar varnish and spar urethane are similar products with similar consistency, one difference that sets the two aside is the fact that spar urethane takes longer than spar varnish to set. A conventional varnish sets faster in comparison to a spar varnish. 

Another difference includes that spar urethane has high resin contents which it cannot be used inside a house or for interior woodwork as it creates yellow hues that are harmful but a spar varnish can be used for interior woodwork too. 

Another difference includes that spar urethane is synthetic in nature and can either be used as an oil base or water base. 

Spar urethane is more long-lasting especially when the wood product is a boat, that is, it does not require a frequent application but it may cost a lot in comparison to spar varnish which requires a frequent application and is inexpensive. 


How To Apply Spar Varnish?

Here are some steps to follow if you want to make it work.

1. Clean the surface with a solvent

2. Apply a thin coat of spar varnish to one side, and let it dry for 10 minutes

3. Turn the piece over and apply another thin coat on the other side, let it dry for 10 minutes

4. Repeat this process until you have applied at least 3 coats of spar varnish to each side

5. Let the final coat dry overnight before applying any more coats or using your project in any way

How To Apply Spar Urethane?

Sometimes, you may need an expert painter’s help but for DIY, follow the steps below –

1. Clean the surface to be coated with a degreaser

2. Apply primer to bare metal surfaces

3. Shake the can of spar urethane well before use

4. Spray on thin, even coats until desired thickness is achieved 

5. Allow each coat to dry thoroughly before applying the next coat 

6. Wait at least 24 hours after the final coat has been applied for the product to cure completely

How Long Does Spar Urethane And Spar Varnish Last?

The Spar Urethane lasts between 10 to 15 years.

The spar varnish can also last up to 15 years, but the urethane lasts longer if you know how to apply it correctly.

If you’re looking for a finish that is more durable than paint, sparing polyurethane might be what you need on your kayak seat or pad!

Spar Urethane will help protect against scratches and splinters while also being water-resistant which means it’s an excellent option if you plan on using your boat in saltwater often. It comes with UV inhibitors so it won’t crack as regular paint would after time and exposure to sunshine as well as mildew prevention agents. So any grooves left behind by moisture will not hold onto dirt or bacteria as they would.

Which Is Better Spar Urethane VS Spar Varnish?

Both are good in their respective applications.

Both spar varnish and spar urethane come in various sheens and colors – for example, spar varnish comes in satin, semi-gloss, and gloss finishes. The difference between the two has to do with how they’re applied. Spar urethane is used as a protective sealant, whereas spar varnish is more of a finishing product, which can be used over the top of any surface.

Is Spar Urethane The Same As Marine Varnish?

There are three types of varnishes that can be used on a boat hull: spar, marine, and polyurethane.

Spar varnish is a type of marine varnish that is generally composed of natural oils and resins. It was the only type available when boats were made from wood.

Polyurethane is the newest type of coating for boats and it looks like spar varnish but it doesn’t make your boat shiny as a spar does. Marine varnishes are usually not shiny because they have to resist weathering from the elements. Polyurethane, in contrast, is easy to use and can also be applied over existing paint jobs without removing them first.

Do I Need To Sand Between Coats Of Spar Urethane?

One of the most common questions we get is about whether or not you need to sand between coats.

There’s no need to sand in-between coats of spar urethane. The finish will level out and be smooth when dry – ready for the next coat.

The only time you’ll want to sand in-between coats is if you’re experiencing a lot of orange peel, which means you may have applied too much product or sprayed too thickly and it needs to be scrubbed off with some TSP or a similar heavy-duty detergent to remove the build-up, then re-sprayed at a lower spray volume before applying another coat.

Can You Put Spar Varnish Over Spar Urethane?

Yes, you can apply a coat of spar varnish over your spar urethane.

Spar varnish is typically used to seal and protect the surface of the wood. It will help protect your spar urethane from UV damage, moisture, and other outside elements.

Does Spar Varnish Turn Yellow?

Spar varnish does not turn yellow if you keep it in a cool, dark place. But if it’s exposed to sunlight for long periods of time, the UV rays can change their color.

Which Is Better Oil Based Or Water Based Spar Urethane?

Oil-based polyurethanes are made from an organic solvent and a polyol. These products can be difficult to remove from skin, clothes, and tools.

Water-based polyurethanes are made with water, which is much safer than oil-based products. Oil-based products can create a fire hazard because of the heat generated by mixing the two ingredients.

Both oil and water-based products have their own set of advantages over the other type of products. The decision comes down to personal preference for handling, safety, and properties you are looking for in a finish coat.

What Is The Difference Between Spar Urethane And Polyurethane

Spar urethane is a type of urethane that has a density of 0.9 g/cm^3. It is often used in snowsports and surfboard production because it has excellent abrasion resistance.

Polyurethanes are more widely used in construction materials, such as sealants, adhesives, coatings, insulation materials, and packaging. Polyurethanes are also used in making golf club heads, boat hulls, and many other industrial applications.

There are four types of polyurethane finishes. They are matte, satin, semi-gloss, and high gloss.

So what’s the difference between spar urethane and polyurethane? Spar Urethane is tough, durable, and resists extreme weather conditions. Polyurethane is more flexible than spar urethane.


Studying spar varnish vs spar urethane – the differences we come to the conclusion that both these components are used for similar reasons. While the latter is more concentrated and is limited because of the same, the former is more conventional in nature and can be used more extensively. But since they both are perfect in some way or the other, the usage totally depends on the requirement and circumstances!


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Rockey is a kayaking enthusiast who has been kayaking with a local group for the last five years. He loves using kayaks while out on outings on the water or camping when the friends want to have a BBQ party somewhere on the bank of a local lake. More About James R Rockey at About Page Here: Authors
Based on his experiences with the different types of kayaks, he is sharing his opinion about kayaking tricks and required gears so that a beginner can get started right away.
Find his team on Twitter here. Happy reading!

Last update on 2023-03-20 / Affiliate links / Images from Amazon Product Advertising API

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