No matter how gorgeous your woodworking project is, you know that it can all be for nothing if you don’t use the right protective coat.

While this is typically an easy task, some products try to trip people up. The urethanes are one such example.

Indeed, products that sound the same can be used interchangeably, right? Well, that is mainly true, but some key differences make picking spar urethane vs Polyurethane slightly tricky.

So, we’ll explain their main differences and when to use each for excellent results.

What is the Difference Between Spar urethane and Polyurethane

The difference between polyurethane and spar urethane is that Spar urethane is a more water-resistant finish. It can easily be applied in high humidity conditions, where polyurethane might fail if not given time to cure before the humidity rises.

But Spar urethane paint is more sensitive to chemicals and alcohol than polyurethane. When these chemicals are used to clean the surface of the wood, their effect on the finish may be detrimental.

Polyurethane, on the other hand, is resistant to most chemicals, including ethanol.

What is Spar Urethane?

Spar urethane is a special type of varnish that was originally meant for boats. The older version was called spar varnish, as it was applied on the spar of sailing boats.

As you would expect, these products are waterproof and resist UV light rather brilliantly. However, for the product to become more suitable for interior use, manufacturers started adding urethane plastic as part of the resins, thus came spar urethane.

Fortunately, the urethane did not stop it from being UV and water-repellant. Now, you can use spar urethane for many interior and exterior woodworking projects, especially the surfaces exposed to a lot of moisture and sunlight.

There are two main types of spar urethane:

  • Oil-based spar urethane
  • Water-based spar urethane

Spar urethane is a durable finish that will also protect your wooden surfaces from scratches, dents, and chemical spills.

Both types of spar urethane accomplish the same tasks, but oil-based spar urethane dries slower, has a more pungent smell, and tends to yellow over time.

What is Polyurethane?

Polyurethane is a durable, water-resistant finish that dries very hard. It can be used on a wide range of furniture but is mainly used on floors, tables, fences, and other surfaces that need protection from water and scratches.

Given how thick Polyurethane can be, it is rarely used for high-end furniture.

The two main types of Polyurethane are:

  • Oil-based polyurethane
  • Water-based polyurethane

While they both do the same thing, each one has its unique advantages and disadvantages. For example, oil-based Polyurethane gives a warm glow to wood, and it yellows over time.

Water-based poly dries very clear and remains clear. Both can be used to protect wooden surfaces for over a decade when applied and maintained correctly.

Spar Urethane Pros and Cons

Pros

  • Scratch and water-resistant
  • It is easy to apply
  • It dries quickly
  • It has UV blockers

Cons

  • It does not dry very hard
  • It needs to be reapplied occasionally

Polyurethane Pros and Cons

Pros

  • Thick coat that lasts for a very long time
  • Scratch, chemical and water-resistant
  • Dries hard and can handle a lot of wear and tear
  • It can be applied in different ways

Cons

  • It takes a long time to dry
  • Emits high quantities of VOCs 

Polyurethane vs Spar urethane: In-Depth Feature Comparison

Now that we’ve got the niceties out of the way, it’s time to put these two products against each other and see who comes out on top.

But before we do, it is important to establish some glaring differences. Every mainstream spar urethane product can be used both inside and outside the house.

However, Polyurethane is sold as either interior or exterior Polyurethane. As such, interior and exterior Polyurethane have slightly different attributes.

So, to keep it simple, we will be focusing more on the interior use of these products.

Spar Urethane Vs. Polyurethane – Ease of Application

When working with a new product, one of the first things you need to know is how easy it is to apply. Yes, it may look great, but if the method is complex, you are better off sticking with what you know.

A lot of people say that spar urethane is easier to apply than Polyurethane, but that is slightly misleading.

The application process for both products is identical in every way: scuff the underlying surface, clean it up, add the first coat, wait for it to dry, and then add the second coat and repeat as needed.

Some people give spar urethane the edge because the brush strokes are not as visible compared to Polyurethane. This is true because spar urethane is a softer material, so it tends to level better.

However, that is only the case when you’re applying oil-based Polyurethane. Water-based Polyurethane does not have the same issues with brush strokes and dust nibs as the oil-based version. Besides, you can either wipe on or brush on polyurethaneane!

This is an important distinction as many people now use water-based poly more often, even though this caveat won’t change the overall grade.

Verdict – spar urethane by a narrow margin

Urethane vs polyurethane clear coat– Drying Times

This is another hot topic that gets a lot of one-sided answers. However, ask nearly anyone that has used these two products before, and they’ll tell you that spar urethane dries much quicker than Polyurethane.

Again, that’s very misleading.

Polyurethane is notorious for drying way too slowly. One coat can take up to 24 hours before you can apply the next one. One day per coat? Absolutely ridiculous! On the other hand, spar urethane is ready for a subsequent coat in just 4 hours.

That is a ridiculous margin, and it would be tempting to stop the comparison right then.

However, that is only when you are referring to traditional oil-based Polyurethane and not the fast-drying types. Fast-drying, oil-based Polyurethane is dry in as little as 4 to 6 hours, which is a massive improvement.

It is important to note that some companies now only sell their fastest drying oil-based polys, so judging by old standards is obsolete.

As for the water-based versions of both products, they are both ready for a new coat in just 2 hours.

Even the curing times for the water-based options are identical, as are oil-based spar urethane and fast-drying oil-based Polyurethane.

Now, when you consider options like one-coat poly and wipe-on poly, the drying time shrinks even further, thus making it slightly faster than spar urethane. So, all in all, this is a tighter race than imagined.

Verdict – tie

Polyurethane vs Spar urethane – Toxicity

Now, we get to an option without any hope for a comeback. Polyurethane is great at many things and for many things, but the environment is not one of them.

Contained in Polyurethane are isocyanates and other products that emit high quantities of volatile organic compounds (VOCs).

Some VOCs are known carcinogens, i.e Benzene – and they can also irritate the eyes, lungs, and skin during use.

As a result, you need to be extra careful when using Polyurethane, especially oil-based. The only saving grace is that after Polyurethane dries, it is no longer harmful.

Before you get the wrong idea, I must mention that spar urethane also emits high quantities of VOCs, though not as high as Polyurethane. This is true for both the water-based and oil-based versions.

If we compare water-based spar urethane vs polyurethane, it is possible to find a few water-based versions that emit lower VOCs than water-based spar urethane, but this is not common.

On average, spar urethane tends to be much safer for both people and the environment.

Verdict – spar urethane

Urethane vs polyurethane finish – Durability

Now, this is the point of the comparison where we get tough, really tough (pun intended). Fortunately, that is very easy for Polyurethane.

As you probably know by now, Polyurethane is one of the toughest topcoats for interior woodwork. Its unique combination of resins and solvents makes it dry very hard, and it will maintain this firmness for years to come.

This is true of both oil-based Polyurethane and water-based. You will still hear some people say that oil-based poly is tougher, but those are reviewers that are still hung up on older, disappointing versions of water-based Polyurethane.

On the other hand, spar urethane is tough, but it doesn’t dry as hard as Polyurethane. As these products are made for interior and exterior use, they maintain a bit of flexibility.

That is because as the weather changes, outdoor wood will expand and contract. Therefore, the topcoat needs to be able to do likewise without breaking or peeling.

As a result, spar urethane doesn’t dry as hard as interior poly. Consequently, spar urethane is not as durable.

While Polyurethane can last for one to two decades, water-based spar urethane may last five years and oil-based up to thrice as long.

Spar urethane is also more likely to suffer irreparable damage long before that time.

Verdict – Polyurethane

Polyurethane vs urethane – Ambering

When considering the longevity of a product, it is also meaningful to include its desirability. By this, we are referring to the point at which the finish begins to hurt your eyes, and you want a change.

The primary reason why you may want to change the undamaged wood finish is ambering. Oil-based finishes have an amber hue, which gets noticeably darker over time. While this might not be a problem on dark woods, it can be displeasing on lighter woods or light paint colors.

But then, even with darker woods, you may not complain for the first few years, but it may eventually get on your nerves. Therefore, it would be safe to say that ambering should also be considered a part of durability.

In this argument, oil-based Polyurethane has no leg to stand on. It is undeniably yellow and gets more so as it ages. The same is true for oil-based spar urethane.

Let’s look at water-based spar urethane vs Polyurethane.

Where we have a distinction is with the water-based options. Water-based poly is crystal clear and remains that way until the end of time. Sadly, the same cannot be said for water-based spar urethane.

While it is also technically a crystal clear coat, it ambers on light stains and woods. So, before you use it this way, you first need to test it on an inconspicuous part of the surface to ensure it doesn’t yellow.

Does water based polyurethane yellow? To be fair, some cheap water-based polyurethanes yellow when in contact with white paint, and some poor products will yellow, but they tend to behave well on light wood and stains.

Verdict – polyurethane by a comfortable margin

Helmsman-spar urethane vs. polyurethane – Protection from Elements

Now, this is spar urethanes strong suit and probably a slightly unfair comparison. As mentioned earlier, spar urethane was originally made for boats, so it can weather the weather like no other.

Spar urethane can handle UV rays without the woodturning gray, and it can also take a lot of abuse from water.

However, as this is a slightly softer finish than Polyurethane, spar urethane can look milky when exposed to a lot of moisture.

This might make you think the finish is no longer working, but it becomes clear once more when it dries. Polyurethane does not have that problem, but it definitely cannot handle as much moisture or sunlight.

Only exterior Polyurethane normally comes with UV blockers. Interior versions can’t hold a candle to spar urethane.

So, if you need to apply a top coat on interior wood that will be exposed to the sun all day, you’re better off with spar urethane.

Verdict – spar urethane

Spar Urethane Vs. Polyurethane – Versatility

Polyurethane is a wonderful product for many reasons, one of which is its versatility. As it is a very resistant product, it can be used on any wooden surface.

Unfortunately, that is not the same with spar urethane. The significant difference between how to use both products is floors.

While you can apply Polyurethane to wood floors, you cannot do the same with spar urethane. Since spar urethane is a tad soft, it will quickly wear off in high-traffic areas.

Being constantly pounded by feet, furniture, shoes, golf clubs, falling chairs, and everything else will damage it.

On the other hand, Polyurethane dries hard and remains hard enough to handle any form of abuse for years without weakening.

Besides floors, you may not want to use spar urethane on any surface you want to be rock hard. This could be tabletops, kitchen countertops, or coffee tables – if, like me, you tend to rest your feet on them.

As great as spar urethane is, not being able to use it on some of the surfaces that need it most is a bit of an issue.

Verdict – Polyurethane

Can you put polyurethane over spar urethane?

No, you should not put Polyurethane over spar urethane. This is because oil-based Polyurethane or interior varnish have a lower oil ratio than spar urethane. You should sand down the old finish and apply the same finish like the one you’ve removed. This will give you a good finish without requiring any extra work.

Can you put spar urethane over polyurethane?

Yes, as long as it’s completely dry, you can put spar urethane over PolyureSpare. Spar urethanes are a little trickier to use but can be very forgiving and adhere well to multiple types of paint.

We recommend you test the adhesion on a small inconspicuous area first before going all out on your project.

Poly vs spar urethane FAQs

What is spar urethane used for?

Spar urethane is a great topcoat for interior and exterior wood surfaces. Spar urethane has UV blockers and is water-resistant, so it is great for objects that will be exposed to water and/or sunlight. The protective spar urethane forms a barrier against moisture and rain.

Does spar urethane turn yellow?

Oil-based spar urethane will turn yellow, while water-based spar urethane will not yellow. However, some brands of water-based spar urethane turn yellow when applied to light woods and light stains.

Before applying on any light-colored surface, test the spar urethane on a small portion to see if it yellows.

Can I use spar urethane on floors?

No, you should not use spar urethane on interior floors. Spar urethane is flexible because it is designed to expand and contract as the weather changes.

However, floors need a very hard finish due to all the movements and heavy materials they come in contact with.

Is polyurethane better than spar urethane?

It depends on the usage. Polyurethane is great for interior floors while spar urethene is good for outdooor woodworks that will be exposed to too much sunlight and temperature changes.

Spar urethane vs spar varnish

The difference between spar urethane and spar varnish is that spar varnish is known to eventually chalk off or chip over time, while spar urethane can maintain a hard, shiny surface for a long period.

Spar Urethane Vs Polyurethane Verdict

Comparing exceptional topcoats is never easy, especially when they have different purposes.

Therefore, you need to choose based on how you plan to use them.

Use spar urethane when:

  • The wooden surface will be exposed to sunlight
  • When there is a lot of moisture
  • You need a bit of flexibility on the surface
  • Minimizing toxicity is a priority

Use polyurethane when:

  • Working on high-traffic areas
  • You want to protect a surface for years
  • Working on large surfaces
  • Working on light colors

Again, spar urethane was made for a different purpose from Polyurethane.

What to Do Next

Many people are under the impression that lacquer and Polyurethane have a lot in common. They’re wrong. There are some key differences between lacquer and Polyurethane that will make your life easier when choosing which is best for you.

23 thoughts on “Spar Urethane Vs Polyurethane Comparison”

  1. Very helpful article. I’m preparing to replace an old wooden threshold on my front door (ocean-side house in Massachusetts) with a new oak one, and am looking for the most durable finish for this high-traffic application. (The wood will get a dark stain, so yellowing is not a concern.)

    From what you wrote it looks like polyurethane is the way to go, but oil-based or water-based? And although I’d like to save time, is there any benefit to using slow-drying products instead of fast-drying, or disadvantages to the fast-drying ones?

    Also, I’ve found a product called Eco-Poly, which claims to be more eco-friendly than conventional polyurethanes. Thoughts?

    Thanks!

    Reply
  2. Working on a project for outside. Will be exposed to all elements and is a light wood, so prefer no yellowing. What do you recommend?

    Reply
      • Very informative article Goodell thank you. Can I get your judgment on something?

        I’m building a camper set-up (long pull-out drawer under a bed + some cabinets) using sanded plywood in a Tacoma truck bed, and I’m deciding between poly and spar. It seems like this is an “in-between” case –
        1. The wood will be exposed to big temperature changes (+1 for spar).
        2. It will be exposed to a bit of sun, though not as much as backyard furniture since there will be a truck shell with tinted windows over it.
        3. It will be exposed to quite a bit of humidity, and occasionally a small bit of rain water will seep in a few cracks that aren’t quite sealed. (But never more than a little bit of rain seeping in.)
        4. I would prefer the wood doesn’t yellow.

        Deciding between water based poly and water based spar. Pretty much everyone on Youtube who builds similar truck campers go with poly, though that may be in part because it’s better known. Your thoughts?

        Reply
  3. Hi! I exposed the wood floor in my half bath, stained it, and sealed it with an acrylic polyurethane several months ago. I recently noticed a spot where it was pealing. I’m thinking a drop of some liquid must have spilled on it and remained there. So, after I fix that, I’m planning on applying a coat of something that is more durable. What do you think would be the best to use in this situation?
    Thanks!

    Reply
  4. Thank you so much. I’m amazed at all of the information this article has revealed. I’ve made a raised garden box. I chose water based spar urethane for the water resistance and uv protection. I have just assembled it there is no soil in it yet. My concern is food safety and curing time. I herd that its safe once cured. “30 days” then put the soil in True or false. Also is that for inside and out side of the box or do I only do the outside? If its only the outside would I still have to wait 30 days to fill it and plant? The time Is a concern for it’s a suprise gift. Am I barking up the wrong tree with the spar ??

    Reply
  5. Thanks for the article.
    Is there a product that can be applied over an existing spar urethane finish to increase its durability?
    Thanks again.

    Reply
  6. Thanks for a great article! We are refinishing our wooden front door that is protected on a porch for rain but gets a lot of sunlight. Because it’s the main entry to the house, it also sees a lot of wear. The stain will be on the darker side so yellowing is not an issue. Do you recommend spar urethane or poly?

    Reply
  7. I am making a table (40″ X 40″) with a 26″ square butcher-block type center (walnut end grain), wrapped by a 1 1/2″ band of Padauk, and then wrapped with a band of 5 1/2″ walnut board. Legs are basically 4″ X 4″ walnut. Primary use will be as a game table (frequently with coffee and cold drinks). Environment is indoor in Arizona (low humidity). Priorities are moisture protection, handling wear and tear, and UV protection (to protect the color on the Padauk). What are your recommendations on finishing to achieve these priorities in the given environment?

    thanks – scott

    Reply
    • If you really need UV protection, the cost effective method would be spar urethane. Go for oil-based spar urethane if you can handle a little ambering of the color, waterbased if not.
      The other option would be epoxy with UV protection added, and it’s my understanding a normal “bar top pour” doesn’t have it. Typical indoor poly doesn’t either.

      Reply
  8. Thanks for the article. Great advise. I’m building a new cedar patio table for outside, under my deck, so it won’t be seeing that much sunlight or rain but of course be exposed to changes in temperature and humidity. It’s going to get a lot of use, so I was thinking Exterior Poly instead of Spar. Waddya think? Not sure I would like the darkening amber tinit on a new table so would a water based product be just as good?

    Reply
  9. Excellent & helpful article! I have a freestanding (unfinished) butcher block island, with 2 lower slatted shelves. Used in kitchens past 20 years, but now has to be outside, on a covered porch. It has little sun exposure, but can get splattered in windy rains. Including the humidity changes & pollen, ugh. Now has some moldy spotting to it also, from this past fall+winter. Plan to clean some with bleach+water spray+brush, then sand. I’m planning to use water-based polyurethane, as decided thru my preferences of your various categories & comparisons. Am I on the right path ? I did 4get to mention the top has had applications of butcher-block conditioners, several times thru its 20 yrs.

    Reply
    • “Several times” over a 20-year period is probably far too few for a working butcher block. If you plan to continue using it for its intended purpose, poly is not the best choice. Keep oiling it more frequently if you intend to use it for food contact.

      If it’s simply a “table” now, I’d go with a spar urethane instead of indoor poly. Minwax and varathane make one you can get at a box store. Spar urethane has UV protection and a more flexible coating than polyurethane designed for exterior.

      Reply
  10. Thank you for the article. I used an interior water-based Varathane polyurethane on a piece that will be in a garage and inside a vehicle. It will not be exposed to water, snow or UV. It will be exposed to different temperatures. Do you believe the poly will hold up or are the temperature swings going to cause a problem? Thanks for your opinion.

    Reply
    • I used Minwax Gloss for years without any issue…I did switch to spar urethane and use it every week for enclosures that go into cars nationwide…the spar urethane seems to hold its shine a little longer than the regular polyurethane. So Spar is definitely the better option because it’s a little more flexible coating to deal with temperature changes better. Poly will work but spar would be better.

      Reply
  11. I am stenciling a floor in a greenhouse. Being a greenhouse, it will be exposed to seasonal temperature extremes and lots of traffic in certain areas, as well as lots of UV light. The stencil “experts ” told me I should use Varthane spar urethane, but I’m not sure given my unique circumstances. Can you offer your input please?

    Reply
    • Spar urethane is better than poly when it comes to UV protection, water. And it handles extreme temperatures better.

      So, between the two, definitely spar. If you wanted to go “BEST” I’d say epoxy with a UV protectant added.

      Reply

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