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In order to protect your wooden vessel or accessories from the damaging effects of water, it can often be necessary to apply some sort of coating to act as a barrier. That’s where spar marine varnish and spar urethane could be useful.
But what’s the difference between the two products and how do you know which one you should use? We have put together this guide to help explain what the products are and what their benefits might be.
What Is Spar Marine Varnish?
Flexible UV Protection
Spar marine varnish is a natural oil based product that is designed to protect wood. Because of its composition it is can allow wooden surfaces to maintain their flexibility. This can be beneficial for wooden surfaces, as they will be able to bend and expand and contract as needed.
Spar marine varnish is intended for coating exterior wooden surfaces that are above the water line. It can add water protection, UV and heat protection, as well as help to prevent scratches, stains and damage from chemicals or solvents.
The appearance of the finished varnished surface can vary depending on the type of varnish you choose, either gloss or satin. One thing about spar marine varnish is that you will likely need to reapply it regularly as it can often flake off or chip.
The word ‘spar’ is relative to marine, in that it is used as a term for the mast or staff on a ship, so spar varnish should be ideal for marine use, as that is essentially what it is designed for.
How To Apply It
Spar marine varnish can require several coats, with several hours in between each one to allow it to dry completely before the next coat. Natural bristle brushes or foam brushes can be ideal for application. You can also use badger hair brushes, which can give a clean finish on the final coats.
It can be important to varnish your canoe or vessel in an area that’s free of dust, wind or hot sunlight, so that it can stay clean and dry evenly.
Video: Varnishing A Canoe
What Is Spar Urethane?
Spar urethane is similar to spar marine varnish in that it acts as a protective barrier against water damage and moisture. It also has the ability to flex with the wood, expanding and contracting with changes in temperature.
One difference between this and spar marine varnish is that the spar urethane is a synthetic product and can be either oil based or water based.
Spar urethane comes in different finishes, including high gloss, semi-gloss and satin, which can allow you to choose the most suitable one for your needs.
Urethane is resistant to ultraviolet light, meaning it could help to protect your vessel against the harmful UV rays from the sun. For vessels that are outdoors for most of the time, this can definitely be beneficial, as it can help to prevent paint from fading and wood from weakening.
UV light can be particularly damaging to exposed wood. Epoxy products can also be used, yet they may not offer the same flexibility of movement as the spar urethane has, which could mean it may crack if the wood moves.
How Is It Applied?
Spar urethane can be applied to the wood using a natural bristle brush to seal the wood. Just like with the spar varnish, you should apply the urethane in a clean and dust-free environment and ensure that you clean and smooth down your boat first.
Video: Spar Urethane Application
You will probably find that you will need around two or three coats in order to get the best protection.
Spar Varnish vs Urethane: What Is Best For Marine Wood?
While both spar marine varnish and spar urethane can offer water protection for your wooden canoe, boat or paddle, the one that is best for you will likely come down to budget and/or maintenance.
With the high level of moisture protection that comes with spar urethane, this could be a good choice for coating paddles, canoes or other wooden vessels. It may also have a higher level of durability, meaning it could require re-application less frequently than spar varnish, but can often cost more.
Both spar marine varnish and spar urethane have their own benefits, such as water and UV resistance and flexibility, and can be very similar. You may find that with different brands of the products you also get slight differences in the composition, for example added UV blockers to provide additional weather protection for your craft.
Pro Tip: Spar marine varnish may require more coats than the spar urethane in order to gain the best results and durability levels, which can take longer, so patience may be needed.
Hopefully you now know the difference between spar marine varnish and spar urethane. You’ll probably have discovered that they can be pretty similar in the protection that they can give your canoe and the aesthetic appearance.
The main goal is to protect your wooden paddle or vessel from water and weather and both of these products could help you do that.
Let us know if you’ve enjoyed this guide and if you’ve found it helpful. Or if you think some of your followers could benefit from this information, please share it with them.
You may also enjoy our article on painting kayaks: https://kayakguru.com/how-to-paint-kayak and on kayak UV protection tips
14 thoughts on “Spar Marine Varnish vs Spar Urethane For Paddles, Canoes And Small Boats”
I really like it that you suggested using spar urethane as a great coating for paddles, canoes, and wooden boats because it’s highly durable. Grandpa would definitely want his old boats re-coated with spar urethane instead of spar varnish to make his boats’ color, shine, and finish last longer and more vivid. Since he wouldn’t need to repaint it more often, he’d really be saving a lot of money in using this water- and UV-resistant paint for his marine vehicles.
Thank you so much for this information. For my needs I see that spar urethane is appropriate. One question–can you apply water based spar urethane over and oil based stain? Thank you.
I Believe you could but, why would you want to? One of the primary reasons for using such a finish (“spar” finishes)is to protect wood. For the best results, you want it to penetrate deeply and your oil based finishes are definitely the best for that. It gives you greater durability by far.
After 30 years of using varnish, this may be the year to try urethane.
Hi Bill. Give it a go and be sure to update us with the results!
I am wondering if you can apply Spar Urethane over Spar Varnish or would I need to strip down to bare wood and start over?
I’m about to build and outdoor bench. The seat will be hardwood. It will be exposed to the harsh Australian sun and plenty of winter rain. I need to confirm which product to use. The Spar Marine or the Spar Urethane. Even though there will be a bit more up-keep, I’m leaning towards the Spar Marine due to the amount of movement expected of the timber.
Am I on the right track?
The only concern with the varnish option is it tends to be a bit softer in the direct sun/heat. It may stick to your pants slightly or retain an imprint of the fabric. The urethane will dry harder under those conditions. Based on your non-marine need, I would recommend urethane.
I am constructing a wood fire sauna boat with a repurposed 25 foot tritoon. I have purchased marine grade 3/4″ plywood for the deck to build upon. What should I use to seal all six sides of the plywood before screwing it down to the aluminum floor joists?
The MAJOR difference between the two is that Spar Urethane stays on the surface of the wood and acts like a shell. Spar Varnish soaks into the wood to keep the fibers in the wood from drying out.
OK!! I would like to make a comment about the two finishes. Having owned a 1971 Boston Whaler for 30+ years I’ve used both coatings. The seats and console in my Whaler are Mahogany. and I have redone them about every 5 to 7 years. Mostly because of “Use Ware” When I lived on Long Island Sound sand was the biggest issue on the seats. When I moved to a lake in Maine the boat would sit on the boat lift in the beating sun for 3 months. No matter what, owning a boat with wood as long as I have, you will need either of these coatings multiple times. Here is my experience. When I bought the boat the previous owner said he only put a spit coat of polyurethane on the bare wood and I should apply a couple more, so I did. The durability was great and it held a high gloss for a about 5 maybe 6 years. Here is the rub, actually the real hard rub. The urethane was so difficult to remove I spent hours and hours removing it. At least 10 hours of sanding and prep for each of the 3 seats. I spoke with the fella I bought the boat from to see what kind of urethane he used. He told me he never bothered sanding, he always ran the seats through his thickness planer and skimmed off a little wood. That explains why the seats were thinner than factory. I went to Plan B, I bought 11 feet of 6/4 Honduran Mahogany, planned to 1-1/8″ thick and now had 2 correct thickness seats. But this time “No Polyurethanes” just plain old Spar Varnish. I knew this would require more coats and I put about 8 coats on the new mahogany. That only gave me about 4 or so years of great looking shine. Here is the best part when it came time to strip off that varnish I used glass microscope slides as scrapers to remove the varnish down to bare wood and then some light finish sanding and I was ready for a recoat. This time 10 coats, then the next time 12 coats and that was the magic number. I get 7 years easy now, albeit I do use the boat a little less. 12 thin coats with mild sanding between the first 4 does the trick. So my two cents worth is, 20 to 30 hours of hard sanding and prep verses 20+ hours of watch varnish dry I’ll take the latter.
Thanks for the detailed response, George! I’m sure our readers will get a lot of value from it 🙂
Thank you for the helpful and informative information. Your writing is clear, concise, and articulate. I’m going with Spar Urethane.
Hi Mark….Glad to be of help!