Spar Marine Varnish vs. Spar Urethane

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If you have a boat or canoe, your watercraft and paddle or oars will be exposed to the elements and can deteriorate. To protect them and maintain them in good condition, you need to apply a coating of some sort. But what layer to apply?

You need a coating that protects wood. Such a coating will help maintain the mechanical strength of your boat and make it look good. You can use spar marine varnish or spar urethane. They are two types of finish specially designed for use on the outer surfaces of watercraft.

In this post, we take a closer look at the characteristics of spar marine varnish vs. spar urethane and their uses.

Spar Marine Varnish

Rust-Oleum 207008 Marine Spar Varnish, Quart
Marine Spar Varnish (Amazon)

Spar marine varnish offers protection to the outer surfaces of boats from the elements. However, it also allows the wood to stay flexible. It will be free to swell and contract in line with the changes in outside temperature.

Spar marine varnish is meant to use on the parts of your boat above the water. It provides adequate protection from scratches and protects the surface from heat and ultraviolet (UV) rays and chemicals.

You get spar marine varnish in two types of finish – glossy or satin. Each class creates a different appearance to the surface. The varnish tends to flake or peel off over time, so you need to reapply eventually.

Spar Urethane

Rust-Oleum 250241H Ultimate Spar Urethane Water Based, Quart, Satin Finish
Spar Urethane (Amazon)

The common factor between spar marine varnish and spar urethane is protecting a wooden surface from the elements. They also allow the wood to contract and expand according to changes in temperature.

However, spar urethane makes the surface of the wood water-resistant. You can get oil-based or water-based spar urethane, and it comes in hi-gloss, semi-gloss, and satin textures.

The three essential components of spar urethane are oils, resins, and solvents. They may exist in different ratios, and the proportion determines the properties and abilities of the finish.

Spar Marine Varnish: How to Apply it

Hand holding brush painting wooden surface with protective coati

You need to add multiple coats while applying spar marine varnish. It takes a few hours for one coat to dry before you can use the next coat. You can go on applying multiple coats until you achieve satisfactory results.

But ensure that the coating is completely dry before you apply the next coat.

Ensure that the surroundings are entirely dust-free, should not be in direct sunlight, nor have direct contact with moisture. If you want a clean and smooth finish, you should use natural bristles.

Spar Urethane

Spar urethane shares a lot of similarities with spar marine varnish. It protects the surface from damage through water and moisture and allows the wood to flex with temperature variations.

A significant difference is that spar urethane is produced synthetically, and it may be oil or water-based.

Like spar marine varnish, spar urethane also comes in different finishes, usually hi-gloss, semi-gloss, and satin.

Spar urethane offers protection from the ultraviolet (UV) rays of the sun. Since vessels are in the outdoors for most of the day, every day, adequate protection from the sun’s rays is a helpful thing to have.

You can use epoxy products to apply to the wood surface, but you may not as much flexibility. There will be an increased tendency to crack with the movement of the wood.

Spar Urethane: How to Apply it

Restoration of wooden chairs

You can best apply spar urethane by using a natural bristle brush for sealing the wood. Ensure that the surrounding air is free from dust and moisture.

Clean the surface of the wood before applying and smooth it down with fine grain sandpaper or steel wool.

You may need two to three coats to achieve an adequate level of protection.

Spar Varnish vs. Spar Urethane: Which is Better?


Both categories of finish offer a reasonable level of protection for your watercraft. It is spar urethane that provides a higher level of protection to your boat, canoe, or paddle.

This finish will give you the best value for your money in the long run, as it will reduce the chances of the material of your watercraft deteriorating rapidly.  But although spar urethane may be a better choice than spar marine varnish, urethane generally costs more.

Spar urethane offers higher protection from moisture, so it is a good choice for coating the watercraft’s undersides and for paddles as well.

The more regularly you apply spar urethane to your boats’ wooden parts, the more durable the surfaces will become. Also, you need to use fewer coats of spar urethane than spar marine varnish to achieve the desired results.

But since spar urethane is costlier than spar marine varnish, it kind of balances out.

The Decision is Yours

Small rowing boat on white

Ultimately, you have to decide on the level of maintenance you want to do with your watercraft. The cost factor is also critical since there can be a large difference in price between these products.

You can use either or both of these finishes depending on the money you are prepared to spend.

The bottom line is to provide enough protection to boats, canoes as well as paddle surfaces. Without such products and regular maintenance, the wooden surfaces could quickly deteriorate due to UV radiation and moisture.


We hope that you benefit from the information provided in this post. If you have a canoe, kayak, or boat, it is good to know how to maintain them as watercraft does not come cheap.

With such an expensive item, you would want to maintain it adequately to enhance its longevity. The best way of preserving your watercraft is to keep adding a protective coating in many layers regularly.

The best two marine finishes you can use are spar marine varnish and spar urethane. The information in this post should tell you about the benefits of these two types of wood finish to put them to be the best use.