Polyurethane coating is one of the most commonly used finishing materials for furniture and also one of the components of many other solid materials like mattresses and sofa. Some paints also contain polyurethane for extra smooth and shine. Polyurethane is used to acquire a smooth, blemish free texture on the products.
Spar urethane, on the other hand, is commonly used on wood that is commonly exposed to the light, heat and sun. This is also a common finishing used for things that are submerged in water like boats because of its resistance to water.
Spar Urethane vs Polyurethane: Differences
One of the most common differences between the two is the amount of oil mixed with them.
Spar Urethane tends to have more oil mixed with it; therefore, it is also called long oil varnish. Due to a large amount of oil on spar urethane, it tends to be softer and pliable, unlike polyurethane which is hard and stiff, due to the lesser amount of oil in its mixture.
In applying polyurethane, one must consider the stroke, direction, and style of application. Wrong or improper application of polyurethane may cause bubbles or brush strokes.
Some craftsmen use thinning method to acquire a smooth surface; however, this might also need multiple applications and layers. Polyurethane also dries slowly, therefore, making the work duration longer.
Spar Urethane is considered to be much easier to apply than polyurethane. It is applied in the same manner like polyurethane; however, it tends to dry faster and doesn't require a lot of layers and application to achieve a shiny finish.
Spar urethane cures by oxidation, not by drying, so make sure air circulates.
Should be noted that while the spar urethane doesn’t have as many fumes during application, the smell will take much longer to cure out than a polyurethane finish. (Luke Greer - paint expert)
Spar Urethane and Polyurethane: Pros vs Cons
Polyurethane gives off a smooth, satin-like finish on the product. It goes well on hard objects specially rubbers and metal.
Polyurethane is also more resistant to harsh environments and oxidation that causes wear on the finish. It is also longer lasting and produces a fine quality result.
Spar Urethane, on the other hand, is more preferred to be used for surfaces that are susceptible to harsh conditions like the weather.
Spar urethane also has a low level of toxicity and doesn't produce strong fumes or odor. One of the best qualities of spar urethane is the UV blockers that enable it to prevent wear, fading, or yellowing of the surface as time goes by. It is also a water-resistant compound, which is why it is used mostly used on boat finishing.
One of the major cons of polyurethane is the strong fumes and odor that it emits during application. Too much exposure to the fumes often results in dizziness and headache, as well as difficulty in breathing.
It also requires careful application to avoid air bubbles and brush strokes from appearing on the surface.
Oil-based polyurethane will require more time to dry than a water-based polyurethane.
Since it is also a very resistant compound, removing polyurethane from surfaces for re-touch, refurbishing or cleaning could be a hard, messy task.
One of the difficulties in using spar urethane is that it doesn’t mix well with oil-based products like paint, especially paints with polyurethane. This often results in unbalance in color upon application.
Though it doesn't produce fumes or odors as strong as that of polyurethane, it could still affect one's health if the workspace is not a well-ventilated area.
Exposure to too many fumes could result to nausea, headache and breathing difficulty.
Safety Tips to Remember When Using Spar and Polyurethane
It's a given rule that we should always be careful while working. Here are the tips that you should keep in mind when using Urethane products.
Be Alert and Prepared in Case of Fire
Urethanes are flammable compounds and could easily catch fire. Make sure to have an extinguisher ready on your workplace.
Proper Gear and Clothing
Make sure to wear comfortable clothes that allow easy movements to avoid accidents in the workplace. It is also advised to wear mask and goggles as protection from the fumes that might affect your sight and breathing.
Cleanliness and Workplace
Make sure that the workplace has a good ventilation that allows good air passage to avoid suffocation. Also, maintain a clean and orderly workplace. Make sure that no tools are littering on the ground to avoid chances of tripping or having an accident. Cleanliness must also extend to post-work, making sure that all of the tools and compounds used are properly stored.
Both spar urethane and polyurethane are good compounds that you could use to achieve fine quality finishing.
In using either of them, you need first to consider the material to which you will apply it. Second is the condition that the material will be exposed to.
If you're only working on a small home workshop or basement without a very good ventilation system, it is much better to use spar urethane since it doesn’t emit too many fumes.
You could also avoid health risks specifically if you’re living with children, old people or people with respiratory problems and allergies.
Consider using water-based coating if your workshop does not have a well-ventilated system; you could leave it dry naturally.
If you have a large workspace that allows good air flow, polyurethane is advisable to use since the fumes will circulate properly and flow with the air in the surroundings.
But if you want to make sure that you’re using the right product on your material, you could always ask your local hardware store for advice. Tell them the project you’re doing, the type of material used, the purpose of the material, etc.
They could give you good advice on the product fit for your work. They could also give you inputs and techniques with regard to the application of either spar urethane or polyurethane.
Did the article help you understand and learn more about both polyurethane and spar urethane? Have you decided which of them to use? Share your project and insights with us in the comments section and help your fellow craftsmen understand these compounds.
Have you discovered a technique in applying polyurethane or spar urethane? Help your friends by sharing your discovery together with this article. We can't wait to see your next project!
Extremely helpful breakdown of the two products without all the non-sense you don’t need. Your summery was also a nice touch to wrap things up. My project happened to be removing the paint from a Guitar neck and going bare with a light cover of protection. I choose to go with the Spar over the Poly. So far, I’m very happy with the results and the product was very easy to use.
The pro’s & cons, gave me the information I needed. I’m making a Traditional Long bow With a Fiberglass backing. After reading Article I chose the Spray-on Urethane. For It’s Flexibility, water Resistance,and the Durability.
Thank you, Wayne!
Thank you, Jim!
Very clear, very useful. Thank you for this
Thank you, Brian!
Should be noted that while the spar doesn’t have as many fumes during application, the smell will take much longer to cure out than a poly finish.
Thank you for the useful information, Luke.
Is it advisable to use spar urethane on teak as compared to Teak Oil or is there too much natural oil in the teak? Thanks, Rob
Honestly, I haven’t used it on teak; but I think it would be really oily. Stick with Teak Oil.
Can spar urethane be used on metal outside decorative wall decorations?
I’ve not tried it on such surface. I’m not sure, but I think that you should avoid it.
I have a wooden staircase and the top rails have become to look and fell like an “alligator” finish. I refinished them maybe 5 or 6 years ago using Helmsman® Spar Urethane finish, but in hot and humid weather in the summer, they get soft and “sticky” and caused this problem. Would you suggest I take the surface back down to bare wood and use Polyurethane for a tougher finish?
The situation does require further investigation, but I think you’re on the right track. I’d agree with your solution.