Spar Urethane vs. Polyurethane


What Is Spar Urethane And Polyurethane?

What are spar urethane and polyurethane? What are the differences? How are they used? Why does this matter? Spar urethane vs. polyurethane and which is better?


Spar urethane is a clear protective finish for exterior and interior wood that may be exposed to sunlight, weather, and changes in temperature. It helps protect against UV rays that cause fading and graying effects to wood.

Polyurethane is in liquid form until it dries. It comes in both water and oil based and in a variety of finishes. Water-based polyurethane has a low odor and toxicity level. Polyurethane goes on clear. Water-based polyurethane cannot stand up to extreme heat, so for furniture near high heat, you should use an oil-based polyurethane.

Which Urethane Is Better To Use?

When doing projects and looking for the final finishing to protect your hard work, you might be asking yourself what the better urethane product to use is? Spar urethane that is water-based, or polyurethane that is oil-based.

Using Spar Urethane


When using spar urethane, make sure to stir occasionally during use. Using a high-quality bristle brush, apply a thin coat of the spar urethane to seal completely. Allow to dry for 4-6 hours. Sand the surface lightly with very fine sandpaper.

Apply a second coat and allow to dry completely. If you want more coats, sand between each coat of spar urethane. Before using the piece, allow sitting for 24 hours to dry and seal completely.

Using Polyurethane

When using polyurethane, start with a clean surface that’s been sanded. You’ll need to have a well-ventilated room when working with polyurethane. To seal the surface, mix your polyurethane with mineral spirits and apply a thin coat evenly with a natural bristle brush.


After 24 hours, apply two coats of undiluted polyurethane to the surface. Use long strokes following the direction of the grain. Once the polyurethane has dried for at least 12 hours, go in and remove any bumps or drips with a razor blade.

Before 48 hours, apply your last coat of polyurethane. Keep in mind, if you choose to wet-sand at this stage, you will have to polish the surface.

Pros And Cons

There are many different sides to using spar urethane and polyurethane products. When you are looking at what you want for your product and what would be best to use around yourself and family, these pros and cons might make you lean towards one or the other.

Pros And Cons Of Using Spar Urethane

The pros of using a water-based spar urethane are the low levels of toxicity and odor. It is durable and long-lasting as long as the furniture if maintained. Can be used inside and outside and can withstand the weather.


The cons of using a water-based spar urethane are the paint won’t stand up to oil-based polyurethane. The colors won’t match as well or take as well to a water-based spar urethane. Spar urethane can’t stand up to extreme heat conditions. It has a slight tint to it, so it doesn’t match completely.

Pros And Cons Of Using Polyurethane

The pros of using an oil-based polyurethane are the durability, long-lasting, and high-quality finishes on wood. It can withstand high heat, weather, is waterproof, and will protect from the sun’s harmful damage.


The cons of using an oil-based polyurethane are the high levels of toxicity and odor can cause you harm and requires you to be in a well-ventilated area. Can get air bubbles in the finish and can be easily messed up. Removing polyurethane from wood can be tricky and time-consuming.

Final Thoughts

While spar urethane and polyurethane are similar, they both have unique and different qualities and characteristics that make them great products. Depending on what you want to use and where you are placing your final pieces, will determine the route you take.

If you have children or pets, and not a large enough space to be well-ventilated, you may want to choose the spar urethane that is low odor and low toxicity. This is a friendlier option to the non-workshop space family who wants to do projects.

However, if you do have a good workspace and can use polyurethane, then the results will be worth the time and effort that is put into the finishing of your project. For this, you should be very careful with how much fumes you breathe in and taking a break is a great idea between coats.

I hope this helps you in understanding urethanes better, and I hope I covered everything you might have been wondering about. If you do have any comments, questions, or concerns, ask below, and I’ll try to help in any way I can.

What’s your favorite finish for a project? Do you prefer spar urethane or polyurethane? Let me know so we can get all aspects on urethane uses, pros, and cons. Maybe what you didn’t like may have some effect on others as well.

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