We know polyurethane, and so do you. You’ve likely used it on woodworking projects and may even consider it your first choice for your work pieces. We have a general idea of what polyurethane is, too. We know, for instance, that polyurethane is composed of polymers and urethane (poly + urethane = polyurethane).
This “spar” thing, though, is something different. We know that sparring is practice fighting – boxers spar as preparation for a professional fight. I’ve sparred as a martial artist for 30 years, although I’m a bit old for that now.
But, spar urethane? What is the urethane fighting with? Or does it mean something different?
Key Points:
- Regular, ongoing maintenance of a Spar Urethane finish will help you enjoy many years of protection for your outdoor use beyond the 2-5 years (depending on the type used and climate) you can otherwise expect from the product.
- Spar Urethane, also called Spar Varnish, is a popular finish for outdoor wood projects and boats. It forms a protective coat against the elements that includes shielding wood from UV light.
- There are two types of SU: water-based and oil-based. Each has its pluses and minuses, so read on to help you choose the right one for the job.
What Is A Spar?
- Durable, poly for outdoor wood surfaces such as furniture, doors, windows, fences, trim and more
- water based formula is easy to apply and cleans up with soap and water
- Dries to the touch in 30 minutes and covers up to 87 sq. ft. per quart, recoat after 2 hours
- supports the Weather and UV , top coat does not yellow and helps against natural elements
The word “spar” has several meanings, but the most common ones are:
- A strong pole, especially one that a sail is attached to on a sailing ship. We’ll stick with this one for continuing discussion, but the others are interesting, too.
- A boxing match or session in which two boxers practice their moves without landing any serious blows.
- A tree used as the highest anchor point in a high lead cable logging setup.
- A nonmetallic mineral that is often used in jewelry.
The word “spar” comes from the Old English word “spear”, which means “pole” or “shaft”. It is thought to have originally referred to the long, slender poles used in archery.
In the context of sailing, a spar is a long, strong pole that supports the sails. The main spars on a sailing ship are the masts, booms, and yards. The masts are the tallest spars, and they support the sails that provide the ship’s forward motion. The booms are attached to the bottom of the masts, and they support the sails that control the ship’s direction.
The yards are attached to the masts, and they support the sails that catch the wind and provide the ship’s power.
What Does “Spar” Mean In Spar Urethane?
Now that we’ve established what a spar is, the term spar urethane is beginning to come into focus.
The word “spar” in spar urethane refers to the fact that this type of urethane is designed to be used on spars, which are the long, strong poles that support the sails on a sailing ship. It is a very durable and weather-resistant finish that can withstand the harsh conditions that spars are exposed to.
It is also a flexible finish, which means that it can expand and contract with the wood as the wood expands and contracts due to changes in humidity and temperature.
It’s a type of polyurethane, also sometimes called Spar Varnish, which is a synthetic resin that is made from a combination of polyols and isocyanates. Polyurethanes are known for their durability, flexibility, and water resistance.
Spar urethane typically contains a high percentage of resin, which gives it its durability and weather resistance. It also contains additives that protect the finish from UV rays, which can cause wood to fade and crack.
It is a popular choice for finishing outdoor wood projects, such as decks, outdoor furniture, and boats. It is also a good choice for indoor projects that will be exposed to moisture, such as kitchen cabinets and bathroom fixtures.
Here are some of the benefits of using spar urethane:
- Durable and weather resistant
- Flexible
- UV resistant
- Easy to apply
- Long lasting
If you are looking for a durable and weather-resistant finish for your outdoor wood projects, this is a good option. It is easy to apply and will last for many years.
What Is The Composition of Spar Urethane?
It is a type of polyurethane finish that is designed to be used on outdoor projects – decks and outdoor furniture. It is a clear finish that is made from a combination of resins, oils, and additives. Its specific composition can vary depending on the manufacturer, but it typically contains the following ingredients:
- Resins: The resins in it provide the finish with its durability and weather resistance. The most common resins used are alkyd resins, oil-modified urethanes, and water-based urethanes.
- Oils: The oils in it help to protect the wood from moisture and UV rays. The most common oils used are tung oil, linseed oil, and soybean oil.
- Additives: Additives in it help to improve the finish’s performance. These additives can include UV stabilizers, fungicides, and mildewcides.
It’s a clear finish, but it can be tinted to any desired color. It is typically applied with a brush or roller, and it dries to a hard, protective finish. It is a long-lasting finish that can protect wood for many years.
Here are some of the drawbacks of using spar urethane though:
- It can be difficult to remove.
- It can be flammable.
- It can emit fumes during application.
Overall, SU is a good choice for finishing outdoor wood projects that need to be protected from the elements. It is durable, long-lasting, and easy to apply. However, it is important to be aware of the drawbacks of spar urethane before using it.
What Types of Spar Urethanes Are There?
There are two main types: oil-based and water-based.
Oil-based spar urethane is the traditional type of SU. It is more durable and weather-resistant than the water-based type, but it is also more difficult to apply and remove. Oil-based SU typically contains a higher percentage of resin, which gives it its durability and weather resistance. It also contains additives that protect the finish from UV rays, which can cause wood to fade and crack.
Water-based spar urethane is a newer type that is becoming increasingly popular. It is easier to apply and remove than the oil-based version, and it is also less likely to yellow over time. Water-based SU typically contains a lower percentage of resin, which makes it less durable than oil-based.
However, it is still a good choice for projects that will be exposed to moisture or harsh weather conditions.
Here is a table that summarizes the key differences between oil-based and water-based spar urethane:
| Feature | Oil-based spar urethane | Water-based spar urethane |
|---|---|---|
| Durability | More durable | Less durable |
| Weather resistance | More weather-resistant | Less weather-resistant |
| UV resistance | More UV-resistant | Less UV-resistant |
| Easy to apply | Less easy to apply | Easier to apply |
| Easy to remove | More difficult to remove | Easier to remove |
| Yellowing | More likely to yellow | Less likely to yellow |
| Cost | More expensive | Less expensive |
Which Type Is Right For You?
The best type for you will depend on the specific project you are working on and your personal preferences. If you are looking for a durable and weather-resistant finish for an outdoor project, the oil-based type is a good option. If you are looking for a finish that is easy to apply and remove, choose a water-based type.
Here are some additional factors to consider when choosing between oil-based and water-based SU:
- The type of wood you are finishing. Some woods, such as oak and walnut, are more prone to cracking and fading than others. If you are finishing one of these woods, you may want to choose a more durable finish, such as oil-based SU.
- The climate you live in. If you live in a harsh climate, you will need a finish that is more weather-resistant. Oil-based SU is a good choice for these conditions.
- Your budget. Oil-based SU is typically more expensive than water-based. If you are on a budget, water-based SU may be a better option for you.
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- Protects outdoor wood surfaces such as furniture, fences, railings, trim and more
- Oil based formula provides maximum durability and allows for a more even finish
- Dries to the touch in 2 hours with coverage up to 190 sq. ft., recoat after 8 hours
- Weather and UV resistant formula protects the surface from graying and sun damage
Spar Urethane Drying Time
The drying time of spar urethane will vary depending on the type of spar urethane, the number of coats that are applied, and the ambient temperature and humidity. In general, oil-based spar urethane takes longer to dry than water-based spar urethane.
Here is a table that summarizes the drying times for different types of spar urethane:
| Type of spar urethane | Touch dry | Recoat dry |
|---|---|---|
| Oil-based spar urethane | 2-4 hours | 12-24 hours |
| Water-based spar urethane | 1-2 hours | 4-6 hours |
It is important to note that these are just general guidelines. The actual drying time may vary depending on the specific conditions.
Are Polyurethane And Spar Urethane Interchangeable?
We know there are both water-based and oil-based polyurethanes, and we’ve written about this in past articles, including this piece on choosing the right type of polyurethane for your project. We know why we choose an oil-based polyurethane over water-based when using it to finish hardwood flooring; we know why we choose water-based over oil-based polyurethane for other projects. Water-based and oil-based polyurethanes each have their own pros and cons.
But what is the difference between it and SU? And if different, what are the differences?
They are both clear finishes that are used to protect wood. However, there are some key differences between the two finishes.
SU is a type of polyurethane that is specifically designed for outdoor use. It is more durable and weather-resistant than other types of polyurethane, and it can withstand the harsh conditions of the outdoors.
It typically contains a higher percentage of resin, which gives it its durability and weather resistance. It also contains additives that protect the finish from UV rays, which can cause wood to fade and crack.
Polyurethane is a general-purpose finish that can be used indoors or outdoors. It is not as durable as spar urethane, but it is still a good choice for projects that will be exposed to moisture or harsh weather conditions. Polyurethane typically contains a lower percentage of resin, which makes it less durable than spar urethane. However, it is also easier to apply and remove than spar urethane.
Can Spar Urethane Be A Good Choice For Indoor Use?
While it can be used indoors, it is not the best choice for all indoor projects. SU is a very durable and weather-resistant finish, but it can also be quite strong and difficult to remove. This makes it a good choice for projects that will be exposed to moisture or harsh weather conditions, but it may not be the best choice for projects that will be in a living space.
If you are considering using spar urethane indoors, there are a few things to keep in mind:
- The finish may be too strong for some indoor projects. Spar urethane is a very strong finish, and it can be difficult to remove. This means that it may not be the best choice for projects that will be in a living space, where you may want to be able to easily change the finish in the future.
- The finish may emit fumes during application. Spar urethane can emit fumes during application, so it is important to ventilate the area well. This may not be ideal for projects in a living space, where you may want to avoid fumes.
- The finish may yellow over time. Spar urethane can yellow over time, so it is important to choose a clear finish if you want to avoid this.
If you are considering using spar urethane indoors, it is important to weigh the pros and cons carefully. If you are looking for a durable and weather-resistant finish, spar urethane is a good option. However, if you are concerned about the strength of the finish or the fumes that may be emitted during the application, you may want to choose a different finish.
Here are some other finishes that are good for indoor use:
- Water-based polyurethane: Water-based polyurethane is a good choice for indoor use because it is non-toxic and easy to apply. It is not as durable as spar urethane, but it is a good option for projects that will not be exposed to harsh weather conditions.
- Polycrylic: Polycrylic is a clear finish that is similar to water-based polyurethane. It is also non-toxic and easy to apply. Polycrylic is a good choice for projects that will be exposed to moisture, such as countertops and furniture.
- Epoxy: Epoxy is a very durable finish that is often used for floors and countertops. It is not as easy to apply as water-based polyurethane or polycrylic, but it is a good choice for projects that will be exposed to heavy use.
How Long Will Spar Urethane Last On Your Outdoor Furniture?
The lifespan of spar urethane outdoors will vary depending on a number of factors, including the type of spar urethane, the climate, and how well the finish is maintained.
However, in general, spar urethane can last for 2-5 years outdoors.
Here are some factors that can affect the lifespan of spar urethane outdoors:
- Type of spar urethane: There are two main types of spar urethane: oil-based and water-based. Oil-based spar urethane is typically more durable and weather-resistant than water-based spar urethane. However, oil-based spar urethane can be more difficult to apply and remove.
- Climate: Spar urethane will last longer in a mild climate than in a harsh climate. Harsh climates, such as those with extreme heat, cold, or humidity, can shorten the lifespan of spar urethane.
- Maintenance: Spar urethane will last longer if it is properly maintained. This means re-applying the finish every 2-3 years, and cleaning and inspecting the finish regularly.
If you are looking for a long-lasting finish for your outdoor wood projects, spar urethane is a good option. However, it is important to be aware of the factors that can affect the lifespan of spar urethane outdoors so that you can properly maintain the finish.
Here are some tips for maintaining spar urethane outdoors:
- Re-apply the finish every 2-3 years. This will help to protect the wood from the elements and extend the lifespan of the finish.
- Clean the finish regularly. This will remove dirt, debris, and mildew that can build up on the surface of the finish and damage it.
- Inspect the finish regularly. Look for any cracks, chips, or other damage that may need to be repaired.
By following these tips, you can help to ensure that your spar urethane finish will last for many years to come.
Does Spar Urethane Block UV Light?
Yes, it does block UV light. UV light is a type of radiation that can cause wood to fade and crack. Spar urethane contains additives that absorb UV light, which helps to protect the wood from the damaging effects of the sun.
The amount of UV protection that SU provides will vary depending on the type and the number of coats that are applied. In general, oil-based SU provides more UV protection than water-based.
If you are looking for a finish that will provide maximum UV protection for your outdoor wood projects, you should choose an oil-based version and apply at least two coats. You should also reapply the finish every few years to ensure that the wood is still protected.
Here are some tips for choosing the SU that will provide good UV protection:
- Choose an oil-based spar urethane. Oil-based typically contains more UV blockers than water-based.
- Apply at least two coats. The more coats you apply, the more UV protection your wood will have.
- Reapply the finish every few years. The UV protection will wear off over time, so it is important to reapply the finish every few years to ensure that your wood is still protected.
Spar Urethane On Video
We chose this video because it presents using SU and also because the SU is being used to seal a “shou sugi” project. We wrote about shou sugi, or wood burning as a method of sealing wood, and you might find it interesting.
In this video, MinWax Helmsman Spar Urethane, probably the most well-known SU, is being used.
For your outdoor projects, whether a wood deck, outdoor furniture, or some other outside use, a Spar Urethane, sometimes also called Spar Varnish, will serve you well.
Follow our recommendations for regular ongoing maintenance above, and you will enjoy many years of protection for your wood. A Spar Urethane finish will take good care of your work.
Last update on 2023-09-27 / Affiliate links / Images from Amazon Product Advertising API