Besides selecting materials and tools, the right wood finish can add a significant difference to your project’s overall quality. Some beginners might assume that it doesn’t matter whether they use spar urethane or polyurethane, but not all attributes of these products are suitable for every wood surface.
Before you head to the local hardware store, it might be worthwhile for you to check my comparison of spar urethane vs. polyurethane to ensure you select the right finish for your wood project.
About Polyurethane
If you’ve been a woodworker for a while now, there’s no way you haven’t heard of how polyurethane finish works. It is best used as a protective barrier for interior surfaces. This smooth finish is made of synthetic polymer in its water-based or oil-based version.
It has a flexible coating that prevents chipping and scratching. The only problem is that oil-based polyurethane will darken or turn yellow after it dries. Nevertheless, it forms a durable finish that can fight against external elements like mildew and moisture.
And because it seals the wooden surface well, you can count on exterior polyurethane products to last a long time despite exposure to harsh environments.
Although wood materials hold well when you apply polyurethane, it’s crucial to point out that it’s not better than the durability spar urethane can offer.
Polyurethane Types
As previously mentioned, woodworkers can purchase polyurethane products in their water-based and oil-based versions.
Since oil-based poly has combustible components, it produces more toxic fumes than water-based polyurethane.
On the brighter side, oil-based polyurethane offers higher abrasion levels and scratch resistance. Because of these perks, I highly recommend oil-based products for interior wood surfaces.
Meanwhile, water-based polyurethane is composed of non-combustible elements that release fewer fumes. Considering its toned-down nature, many woodworkers see water-based poly as a more environment-friendly option.
Another good thing about water-based polyurethane is it dries faster than products with oil content. Thanks to this, you can apply more coats in a shorter time.
The tricky thing is that oil-based polyurethane has a thicker consistency. So while water-based poly can dry coats for a short time, oil alternatives require fewer coats overall.
Regardless of the difference between water-based and oil-based polyurethane, this finish forms a durable protective layer once completely dry.
Additionally, don’t forget that regular poly differs from Polycrylic (acrylic polyurethane) because it can lead to confusion as you shop.
Pros
It’s not a secret that polyurethane remains popular in the woodworking industry, mainly because it’s a versatile and convenient material around the workshop. Here are some of the perks you can expect when using it:
- It’s scratch and water-resistant.
- You can apply it through brush strokes and spray cans.
- It also works through the wiping method.
- It produces fewer fumes.
- The coating is smooth and durable.
- It holds well against wear and tear.
Cons
Despite the many advantages polyurethane can offer, it has some setbacks that may not be suitable for some wooden materials. You must take note of these disadvantages to know when and where polyurethane will work best.
- Oil-based polyurethane carries strong odor & toxic fumes.
- It has no UV blockers to protect the surface from UV rays.
- Polyurethane produces highly volatile organic compounds (VOC).
- Oil-based polyurethane applications must be in a well-ventilated area.
When to Use Poly
I recommend using polyurethane to prevent grease or oil from seeping into the wood’s surface. It’s also durable against regular water contact and scratches. Here are some areas and pieces of furniture where you can benefit from using it:
- Wooden Floors
- Wood Doors
- Moldings
- Kitchen Countertops
- Dinner Tables
- Cabinets
- Furniture Pieces
If it’s not for water and scratch damage protection, then using polyurethane isn’t the best option to complete the task.
Applying Polyurethane
No matter how many coats your material requires, the great thing about polyurethane is you can apply it by spraying, brushing, and wiping. Regardless if it’s water-based or oil-based, don’t forget that this process must be in a well-ventilated area.
Since the application and drying processes can span several hours, I always suggest working in a dust-free environment and wearing masks to avoid inhaling VOCs. Here are the specific steps you must remember:
- The workpiece should be well-prepped with an even surface. You must ensure that there is no excess on the wood.
- You must sand the wood’s surface with sandpaper (at least 220-grit) to eliminate dents and scratches.
- When applying polyurethane, don’t forget to check for dust particles settling in. If notice these accumulating, remove them right away before it dries.
- Let the polyurethane dry according to the drying time recommended on its label.
- Add a polish on the applied surface for smooth results.
- Make sure to use a high-quality brush for polyurethane applications.
About Spar Urethane
Spar urethanes are often referred to as “spars of the ship” because they have the durability that can protect boat sails from potential damage. True to its name, the word “spar” refers to the wooden poles that support the boat’s sail.
You may not know, but these boat parts are exposed to extreme conditions like ultraviolet rays exposure and changing temperatures. But when spar urethane dries on their surfaces, they undergo oxidization, where wood expands and shrinks according to weather conditions.
Since it contains more oil than polyurethane, other woodworkers refer to spar urethane as a long oil varnish. You can compare it to urethane plastic because it has synthetic elements like solvent and resin. These attributes make the wood finish softer and more flexible.
If you scan today’s market, you’ll encounter two options for this product: water-based and oil-based spar urethane.
What Does it Look Like?
Besides its water-based and oil-based varieties, spar urethane also comes in a wide range of sheens. You should know that higher sheens mean a shiner finish when the application dries.
If you’re aiming for the most shine in your wood finish, my recommendation would be to go for products labeled as “gloss”. For a moderate sheen, you might consider semi-gloss, or if you prefer a subtler sheen, satin would be a good choice.
Since it has an abundant oil component, spar urethane makes the formed layer look softer. It’s a direct contrast to polyurethane which has a hard-looking appearance when dried.
Spar Urethane Types
We all know that oil-based spar urethane is more popular than its water-based alternative. However, these variations can deliver the same durable finish that’s scratch, dent, and UV-resistant.
The main difference is water-based spar urethane dries faster than oil-based options. It’s also important to note that the latter carries an unpleasant scent and develops a yellow tint over time, unlike water-based spar urethane.
Pros
Considering its flexibility, it’s not surprising that spar urethane is sought-after for a wide range of interior and exterior woodworking projects. If you’re wondering how this wood finish can help with your finishing task, check out its perks:
- It can fight against extreme moisture and other weather conditions.
- It has a much thicker consistency than polyurethane alternatives.
- Spar urethanes can resist UV light [1] and scratches.
- Water-based spar urethane has excellent water resistance.
Cons
Although spar urethane carries many perks, it has some attributes that may not suit specific applications. Take note of these downsides to avoid wasting time and money:
- Spar varnish doesn’t mix well with oil-based paint.
- It doesn’t form a hard coating after the drying process.
- Long drying durations and bad-smelling fumes.
When to Use Spar Urethane
The ideal temperature to apply spar urethane is between 50 to 90 degrees. It also works best on exterior woodworking projects like:
- Door Finishing
- Sashes on the windows
- Exterior furniture pieces
I’d strongly advise against using spar urethane in environments where the temperature is either too low or excessively high.
Suggested Readings:
Applying Spar Urethane
The best way to apply spar urethane is through a natural bristle brush. Like polyurethane, this wood finish will also work with a paint sprayer.
If you don’t have those tools available, you can use a clean rag to wipe the spar urethane solution over the surface. All you need to do is mix equal parts of oil-based spar urethane and mineral spirits. Here are the next steps you must follow:
- Apply at least three coats of spar urethane on the surface, regardless if it’s an interior or exterior project. It also applies to unfinished wood materials.
- For a finished material, two coats will suffice.
- After applying the final coat, wait a whole day to dry the spar urethane before using the surface.
Main Differences Between Polyurethane and Spar Urethane
Having given you a brief overview of each type of finish, I will now delve deeper into their distinctions. Let’s explore a detailed comparison between polyurethane vs. spar urethane:
Indoor or Outdoor Use?
Although spar urethane and polyurethane work with almost the same surfaces, they have different attributes that may or may not suit indoor and outdoor applications. Here’s how they differ:
Indoor Projects
It’s a no-brainer that polyurethane suits interior pieces more than spar urethane because it forms a harder coating. It can withstand extended exposure to water and prevents the wood stain from fading.
Between spar urethane and polyurethane, the prior mentioned offer more flexibility. Because of this, you can’t expect polyurethane to fight against cracking and chipping when used outdoors.
Outdoor Projects
When protecting exterior surfaces, you don’t need any final words. Spar urethane is the immediate solution between the two because it has more capacity to handle temperature changes.
When applied, spar urethane is the kind of product that expands and contracts with the wood’s growth and movement. It also includes protective attributes that prevent potential sun damage.
Oil Amount and Shine
When comparing the oil percentage between spar urethane and polyurethane, it’s hard to ignore that the latter lacks in the ratio department. The excellent oil concentration that spar urethane can deliver better shine and coating flexibility.
Compared to other alternatives, spar urethane is more flexible upon drying. So even though polyurethane delivers a harder coating, spar options can work through wood movements better.
Ease of Application
The application process for spar urethane and polyurethane isn’t as different as you think since both products work better when applied with brushing.
When it comes to the oil-based versions of these products, I’ve noticed that spar urethane tends to leave less pronounced brush strokes compared to polyurethane. That said, with the water-based variants of both finishes, this isn’t a concern.
The only reason spar urethane marks slightly higher than polyurethane in the application is that it levels better due to its softer consistency.
Dry Time
If you’re not using fast-drying products, it could take around a day before a typical oil-based polyurethane clear coat dries. Meanwhile, spar urethane of the same variety only takes four to six hours to dry.
The good news is most polyurethane finishes sold in the market today are fast drying. As point of comparison, I can say that its drying time matches with spar urethane.
And if you’re using water-based options from both products, you must know that these variations also dry in a similar time frame of two hours.
Softness and Consistency
As previously mentioned, the excellent oil concentration on spar urethane gives it an edge for softness. However, polyurethane is more rigid, making it more consistent in application than spar urethane despite its thicker solution.
Flexibility and Durability
Since spar urethane has a soft and thick consistency, its flexibility in holding up against changing weather and wood movement is better. Although polyurethane dries with a hard protective layer, materials applied with a spar urethane finish will last longer.
Ambering
The yellowing of your material isn’t a matter of choosing between spar urethane and polyurethane, especially if you’re using oil-based products. You must expect the ambering effect when applying these solutions on light-colored surfaces.
The difference only shows when you compare water-based spar urethane and polyurethane side-by-side. While water-based polyurethane remains on its clear coat over time, spar urethane develops amber tints on light surfaces. (Take a look the best non-yellowing polyurethanes here!)
Smell and Toxicity
Like it or not, the oil-based versions of spar urethane and polyurethane will always carry a particular scent during application. Meanwhile, you won’t encounter these issues with water-based options.
(For more information, find out if polyurethane is toxic!)
Chemicals and Elements Exposure
The edge spar urethane has over polyurethane is it produces fewer VOCs than the latter.
It carries carcinogens that can cause eye, lung, and skin irritation when exposed directly to the solution. Fortunately, this toxicity is only present when the application is wet.
Price
Since polyurethane is more widely available than spar urethane, it’s not surprising that it’s more affordable than the latter. You can also save more money if you buy polyurethane in spray bottles.
Poly and Spar Urethane: Which Suits Your Project?
If you want to know which is the right finish for your project, here’s a comparison of polyurethane vs. spar urethane for different purposes:
Tabletops
Since tabletops are often in contact with cleaning solutions, it’s best to use a poly finish that can withstand water damage and alcohol.
Floors
As you know, spar varnishes are soft and flexible. Because of this, you can’t use it on floor surfaces with high foot traffic. In situations like these, my top recommendation would be water-based polyurethane, particularly due to its quick-drying attributes.
Countertops
Spar urethane offers more elasticity than others. Because of this, it can go against the changing weather conditions that damage most countertops.
Metal
If the metal materials are outside, spar urethane should be your first option. However, interior metal surfaces will require the likes of polyurethane.
Safety Tips For Using Poly and Spar Urethane
Regardless of your choice between spar urethane and polyurethane, this woodworking activity needs caution to avoid unprecedented accidents during the application.
- Apply in a well-ventilated area, especially if using oil-mixed wood finishes.
- Remember to wear proper safety gear, like gloves and masks.
- Prevent skin contact during application to avoid staining.
- Clean and declutter your working space before the process.
When Using Spar Urethane Only
- Wear your protective clothing and gear.
- Stay away from heat and sparks during the application.
- Don’t smoke during the process.
- Don’t apply the solution near open flames.
FAQ
Will spar urethane turn yellow over time?
Yes, spar urethane will turn yellow over time, especially if it’s oil-based. Meanwhile, most water-based spar urethane products are less likely to develop this color. Furthermore, yellowing tends to happen when you apply the solution on light-colored surfaces.
To minimize yellowing, use a UV-resistant topcoat or place the objects in shaded areas. These can help extend the lifespan and maintain the clarity of the finish.
See Also: Will Water-Based Poly Turn Yellow?
How long to wait for the stain to dry before the polyurethane application?
Before applying oil-based polyurethanes, you must wait around eight hours to dry the wood stain. For water-based poly, you need at least 24 hours of drying time.
Is urethane different from varathane and marine urethane?
Urethane is a variation you can buy when shopping for polyurethane. Meanwhile, varathane refers to a brand that sells urethane. On the other hand, marine urethane is a term used for a wood finish used in boats.
Is sanding between coats of urethane required?
Yes, sanding between urethane coats is a must because it enhances the surface’s adhesion for the next coat.
Is spar varnish better than spar urethane?
Although spar urethane and varnish have almost identical compounds, you must know that the varnish is more prone to chipping and chalking off.
Can you apply spar urethane over poly?
As long as the final coat of poly has already dried, you’ll have no issue applying spar urethane over its surface. However, it’s important to note that spar urethane has a higher oil ratio than polyurethane.
What’s the difference between polycrylic, polyurethane, and spar urethane?
Polycrylic and polyurethane are protective finishes used in almost the same manner.
The only difference is the latter is more known for its oil-based alternatives, while the prior-mentioned is only available in its water-based variation. Meanwhile, urethane is a polyurethane variation.
Are spar urethane finishes available in matte?
Yes, spar urethane has matte variations. However, it’s not the most accessible product to find.
More Comparison Articles:
Conclusion
After comparing spar urethane vs. polyurethane products, it’s clear that they don’t cater to the same woodworking projects.
Don’t forget to consider the usage frequency and environment the material is exposed to so that you wouldn’t waste time and money applying the wrong finish. I’d suggest going through this guide carefully to achieve the best outcome.
Robert Johnson is a passionate furniture maker & carpenter, sought after for his knowledge on the craft.
You’ve probably seen his down-to-earth wisdom in USA Today, Bobvila, Family Handyman, and The Spruce, where he has shared commentary and guidance on various woodworking topics.
Robert is the brain behind Sawinery, where he aims to share tips, tricks, and a passion for all things carpentry.
