Can You Use Spar Urethane On Cedar Wood?

Varnishing your wood is an excellent way to increase its durability by protecting it from sunlight, moisture, and insects. Spar urethane is one of the best varnishes used on outdoor furniture to seal and protect it from harsh weather. Also, you can use it on doors, cabinets, and many other outdoor projects.

On the other hand, cedar durable thanks to it’s natural resins that prevent moisture, insects, and other elements from damaging it. Cedar still needs proytection to last longer which leads to the question, can you use spar urethane on cedar wood?

Yes! Spar urethane can be used on cedar without difficulty since it cures and hardens, to create a protective coat against harsh weather, and other elements such as moisture, snow, rain, and UV rays.

Moreover, it has UV blockers that protect cedar against direct sunlight.

You can apply spar urethane by spraying, brushing or wipe on, it’s a vailable in many different sheens.

Keep reading as we discuss cedar and spar urethane, its uses, pros, cons, and, most importantly, how to apply it to cedar.

What Is Spar Urethane?

This transparent sealer protects the wood from moisture and UV rays, keeping it safe and maintaining its beauty. Even more important, it’s thick and hard, unlike other polyurethane finishes, and can be applied with only a few coats.

Types of spar urethane for Cedar include

  1. Water-Based Spar Urethane

This type of spar urethane is clear, long-lasting, and can withstand snow, rain, and different temperatures. In addition, it contracts and expands with the wood’s movement depending on the current temperature and humidity. It also has additives that protect the wood from sun damage caused by UV rays.

Unlike an oil-based spar urethane, it is non-flammable, dries fast, and produces fewer fumes making it safe for the environment.

They include:

  • Minwax® Water Based Helmsman® Spar Urethane

Its special oil expands and contracts with the wood’s movement in different seasons while protecting it from harsh climatic conditions.

  • Varathane Outdoor Water-based Spar Urethane

It protects wood from bad weather and UV rays, making it best for outdoor projects like windows, doors, fences, railings, and furniture.

It prevents the wood from scratching and maintains its beauty over time.

What to know when a water-based is applied on cedar wood:

  • It needs multiple thin layers and takes less time to cure.
  • It gives a clear finish and can easily be cleaned by water.
  • Expensive.
  1. Oil-Based Spar Urethane

Its yellow color boosts the wood’s appearance for a long time.

The formula has volatile organic compounds, making it tough and durable against moisture, snowstorms, and rain. It’s also formulated with additives that protect it against UV light.

On the downside, it’s flammable and produces fumes that are not eco-friendly.

An example of an oil-based spar urethane is; 

  • Rust-Oleum®Varathane®Premium Spar Urethane

It is easy to apply and prevents the wood from weathering and graying by protecting it from the weather and UV rays. It also contracts and expands depending on the weather.

What to know when an oil-based spar urethane is applied on cedar wood.

  • Though it requires less number of coats, it forms a thick layer, which takes time to cure.
  • It produces a yellow tint but darkens the wood over time.
  • Although less expensive, it is difficult to clean and needs mineral spirits.
  • It is prone to dents.

Oil- and water-based urethane can be used on cedar and protect it from harsh weather.

Uses of Spar Urethane

Since spar urethane is resistant to weather elements and hardens to a protective finish, it is ideal for outdoor projects like,

  • Outdoor furniture
  • Fences
  • Windows and doors
  • Railings
  • House trim and boats (above the water level)

Pros of spar urethane

  • Initially, it was designed to conserve the spars of sailing watercraft, making it the best for sealing outdoor projects. Furthermore, it can be used on both indoor and outdoor projects.
  • It’s flexible, expands, and contracts depending on the type of weather. This helps it to resist harsh weather conditions like moisture, thus preventing it from cracking or peeling.
  • It is easy and can be applied in different ways, such as spraying, brushing, or wiping.
  • It’s formulated with additives that block UV rays, preventing the wood from fading or weathering.
  • It protects and improves the look of your wood surface. For instance, an oil-based spar urethane has a yellow tint and glossy look that adds beauty to your surface.


  • An oil-based spar urethane takes time to dry since it’s thick, and you may be required to wait for a long time before applying the next coat, failure to which soft spots will appear on the surface.
  • Spar urethane produces fumes that are not friendly to the environment. Use it in well-ventilated areas wearing a safety mask.
  • Its different chemical composition makes it hard to blend with oil-based paints. Therefore, thinning it with mineral spirit can help it work with other paints.
  • Although it has UV blockers, they may not protect the wood forever, thus turning yellow due to UV rays. Recoating can be done to avoid the yellow hue.

What Is Cedar Wood?

Can You Use Spar Urethane On Cedar Wood?
Image of Cedar Wood

This versatile softwood has a natural resistance to deterioration, making it durable even in places with harsh climatic conditions, thanks to its natural preservatives.

Let’s look at some types of cedar trees

  1.     Cyprian Cedar

As you might have guessed from the name, Cyprian originates from Cyprus and grows in the Troodos Mountains.

It’s indigenous to a small region, making it a rare conifer, and it grows to a height of 2m in ten years. Also, the branches grow in a parallel line.

  1.     Western Red Cedar

It grows to approximately 60m tall and 2.5 wide, where the climate is cool and moist, like in British Columbia and Canada. It’s an attractive wood for indoor projects like wall paneling, windows, doors, ceiling, and sashes. Its firmness makes it best for molding, sauna paneling, and window blinds.

  1.     Northern White Cedar

It is originally from northern America and grows in a pyramid shape with thick branches and plenty of leaves. Although it would instead grow in well-draining soil, it can also survive in different soil types. It is ideal for shingles, poles, rustic fencing, lumber, etc.

  1.     Lebanon Cedar

It originates from the Eastern Mediterranean, like Lebanon, where it grows to a height of 130 feet but, when cultivated, grows 40 to 80 feet and a width of 30 to 70.

It is prevalent in cold areas since it can survive in cold temperatures. Also, it takes longer to grow and grows in a pyramid shape though the uppermost branches create an open flat top as it matures.

  1.     Spanish Cedar

This type of cedar tree is considered vulnerable to extinction because the place it originates from is under siege by organized crime. It’s best for doors, cabinet works, windows, clothing chests, and interior trim.

  1.     Alaska Cedar

This species, also known as false Cyprus, comes from moist parts of the Pacific Northwest and grows well in moist soil. It’s a medium-sized green tree with blue-green or gray-green leaves that fall from branches spaced widely.

Uses of Cedar Wood

  • Cedar’s beautiful appearance makes it the best choice for interior paneling since it adds a beautiful touch to different designs. It’s also durable with minimum maintenance, like cleaning.
  • Cedar is the best for storing clothes since it is moisture-resistant, protecting your clothes. It also has a lovely scent that makes the clothes smell fresh though it may disappear over time, requiring you to sand it after 2 or 3 months. (Sometimes the scent might be too much)
  • Its porous nature makes it easy to absorb sound and can be used for musical instruments like guitars. It can be used to make guitar strings since it’s soft. Red and yellow cedar are mainly used for this.
  • It can be used in areas with high moisture, like bathrooms and ceilings, since it has moisture resistance.
  • It is used for preparing cedar oil through the process of steam distillation. Sawdust and wood chips use this process to make perfume, cosmetics, and agents used to control insects.
  • Cedar has a type of oil that protects your clothes from pests but can also stain them. To prevent this, you can place a block of cedar in your storage place or simply avoid placing them near the wall.
  • Its versatile nature makes it useful in siding, decking, fencing, boat building, and many others. They are lightweight, stable, and durable, making them the best choice for shingles.

Pros of Cedar

  • Durability

The natural resins in cedar make it resistant to decay, rot, and insects. This makes the wood last longer with minimum maintenance. Even better, it is resistant to moisture absorption preventing it from warping or splitting.

Similarly, it lasts long in outdoor projects depending on the type of environment and maintenance. For instance, with proper maintenance and pleasant weather conditions, a cedar deck lasts for 15 – 20 years or more.

  •  Cost

Cedar might be expensive, depending on the species. But, its functions like durability and aesthetic beauty always justify the cost. It’s also cheaper when compared to teak wood.

  • Appearance

Cedar has a beautiful natural appearance, even without staining or painting. It also has a versatile nature that makes it easy to accept and detain different stain types. Even better, it’s available in different textures and grades, perfect for many woodworking projects.

  • Eco-friendliness

Cedar is the best choice for environmentalists since its renewable, biodegradable, and originates from natural sources, making it friendly to the environment.

  • Insulation

It has air pockets inside the grain that protect the wood from high temperatures, preventing it from warping or expanding. Its natural insulator keeps you warm during winter and cool during summer.

Cons of Cedar

  • Maintenance

Cedar requires regular maintenance, like repainting and re-staining, to prevent the color from fading away due to chemical reactions. Sealing and staining your wood might be a better way to ensure longevity.

  • Rotting

Although cedar is durable with the right weather and when properly maintained, at the end of the day, wood is wood and can deteriorate over time when exposed to humidity for a long time. This can be prevented by re-sealing and ensuring your wood is not exposed to excess moisture.

  • Cost

Cedar is very popular, thus increasing its demand; prices tend to rise when the demand is high. Different factors cause the cost of cedar to rise. For example, seasons like winter and summer may influence its cost since it requires proper maintenance to properly dry.

  • Sensitivity

Many people tend to confuse cedar for hardwood due to its unique properties. Cedar is a soft and sensitive wood that may break if you drop a considerable weight on it, and it’s too weak to be used for construction materials. Cedar can also be sensitive to scratches and dents. Re-sealing it can be the best way to protect it.

Benefits of Using Spar Urethane on Cedar Wood

Finishing your cedar wood with spar urethane might be an excellent way to protect it. Let’s look at some of the benefits of using it.

  • The sun has UV rays that can harm the wood by causing discoloration and cracking the wood. Luckily, spar urethane has blockers that prevent direct sunlight from penetrating the wood by blocking UV rays.
  • It gives a new look to cedar wood projects by highlighting the wood grain and adding a glossy appearance to the wood.
  • Spar urethane increases the durability of cedar since it forms a protective layer that prevents insects and moisture from traveling through it, thus preventing the wood from rotting.
  • Water-based spar urethane is easy to apply. It also produces fewer fumes making it safe for the environment. More coats can be applied in a short time than oil-based ones.

How to Apply Spar Urethane on Cedar Wood

  • Tools and materials needed.
  • Gloves
  • Face mask
  • Spar urethane (oil-based or water-based)
  • Cedar furniture (woodwork)
  • Clean rags
  • Paintbrush/sprayer/bristle brush
  • Sandpaper (120,320,400 grit or finer sandpaper)
  • Mineral spirit, if you are using an oil-based
  • Denatured alcohol for water based
  1. Preparation

Place the woodwork in a well-ventilated place, and wear a mask and gloves to prevent the spar urethane from touching your skin, causing irritations.

Note: Spar urethane coats dry faster when it gets proper air circulation. In addition, a well-ventilated place helps reduce fumes and harsh chemicals released during the application.

Use a clean rag and wipe the cedar surface to remove grease, debris, dirt, or dust. This is an essential process since dirt and dust can stick in the urethane coat, ruining the wood’s look or reducing durability. In case the dirt is stubborn to remove, use trisodium phosphate.

Let the wood dry. Your cedar wood is now clean and ready for the next step!

  1. Sanding

Sand the whole surface using 80-grit or 120-grit sandpaper to smoothen the surface. Next, sand along the direction of the grain with minimum pressure to prevent scratching or leaving marks on the surface. Finally, carefully clean the wood with clean rags without leaving any dust on the surface.

Note: sanding makes urethane stick into the wood by opening the cedar’s porous surface.

  1. Thinning

Thinning helps to get smooth, thin, uniform coats of spar urethane on your cedar surface. It also makes the application and absorption easier since it speeds up drying.

However, thinning is not compulsory, especially when spraying (a sprayer produces thin coats). It’s only applicable when brushing or wiping on it.

Use mineral spirit to thin an oil-based spar urethane and denatured alcohol on water-based spar urethane.

Depending on the type of spar urethane you are using;

Mix four parts of an oil-based urethane with one part of mineral spirits in a container, and mix one part of denatured alcohol with 4 parts of water-based urethane.

Note: Mixing denatured alcohol with water-based spar urethane increases evaporation, quickly drying the coats. The same applies when an oil-based urethane is mixed with mineral spirits.

You are now ready to apply!

  1. Apply the first coat

Choose the method you are going to use in the application. Either spraying, brushing, or wiping on.

Note: Make sure you apply along the course of the wood grain. This makes spar urethane soak into the wood and form a uniform finish. Test it on an extra piece of wood before applying it to minimize mistakes.

Apply the first coat of spar urethane slowly and carefully without missing any part of the wood. The first coat gets absorbed quickly since cedar accepts spar urethane.

Let the coat settle for 30 minutes before wiping the excess spar urethane with a clean rag. (This helps the coat to get a uniform finish and dry fast.

Note: Shaking the spar urethane when applying causes bubbles to get trapped in the spar urethane, creating bumps on your finished cedar surface. Avoid synthetic brushes since they contain air that releases bubbles to the surface. Use a bristle brush instead.

  1. Let the first coat dry

The drying process can take a day or more, depending on the thickness of the coat or the type of weather. Generally, thick spar urethane takes more time to dry than thin ones. (Water-based spar urethane dries faster than oil-based ones.)

Make sure the surface has dried completely before moving forward. Minimal mistakes made on the first coat can be corrected when applying the subsequent coats.

  1. Lightly sand the spar urethane coat.

Use 320-grit/400-grit sandpaper to gently sand along the direction of the wood grain.

Note: Sand lightly to avoid damaging the coat; this prevents the layers from separating, making the finishing coat thin, pleasant, and smooth. Generally, sanding makes the surface smooth and creates a better adhesion between the coats.

Clean the whole surface using a clean rag to remove the dust particles.

  1. Apply the successive coats

Use the same procedure you used when applying the first coat to the subsequent coats. Apply a minimum of 3 coats to a maximum of 5 coats, and make sure the coat dries before adding the next one.

Apply thin, even coats.

  1. Leave the coats to dry and cure

Let the final coat dry for a day and give it 3 days or more to cure. Make sure it has cured completely before using it. No need to sand the final coat.

Well, your project is now ready! And even better, with a protective coat and lovely appearance.

Note: applying spar urethane on a surface that has not dried spoils the wood’s appearance reducing the protection needed.

Here’s A Video On How to Apply Spar Urethane:

How Long Does Spar Urethane Last Outside?

Spar urethane finish takes about 2 or 3 years before the need to re-apply. On the contrary, spar urethane lasts over ten years with correct cleaning and maintenance.

To be on the safe side, re-apply spar urethane at least once in two years to protect the wood from harsh weather like moisture and UV rays.

This helps the wood to maintain its natural beauty and remain fresh.


To maintain the original color, Remove the old layer and apply a new one in case your furniture darkens or gets amber-toned.

In addition, spar urethane lasts outdoors for 5 years after the can has been opened. Avoid storing the spar urethane in a dry place and full of dust to keep it safe from any damages saving you the cost of buying a new one when you need to re-apply.

How Do You Protect Cedar Wood Structures Outdoors?

Luckily, cedar has the advantage of durability since it’s naturally resistant to moisture and UV rays. However, because of different weather elements, you will still need to protect and maintain it to increase its durability on outdoor projects. Here’s how to protect cedar structures outdoors;

  • Cover your cedar structure with a waterproof sealer, like spar urethane, polyurethane, Tung oil, or varnish, on your cedar wood to create a protective coat and keep it safe from different weather conditions such as moisture and sunlight.
  • Protect your wood from moisture by drying the screws and bolts to prevent rust stains. Also, avoid placing your cedar structure in moist areas such as rooms with excess sunlight since sunlight builds up moisture on cedar wood.
  • Regularly hand wash your cedar with mild bleach/detergent, a soft rag, and a water solution to wash away mildew and stains. Let the wood dry before applying your sealant or stain. Also, cleaning increases your wood’s durability maintaining its beauty and natural scent.

How Do You Weatherproof Cedar Wood?

The best way to weatherproof your cedar wood is by sealing or varnishing it. Spar urethane is one of the varnishes used to weatherproof cedar.

The air outside reacts with spar urethane, polymerizing and forming a protective coat that makes cedar weatherproof and resistant to snow, rain, and harsh weather elements.

Mix and thin spar urethane with denatured alcohol or mineral spirits, and apply three thin coats of the solution on your cedar wood.

Sand lightly between the coats and allow every coat to dry for a day before applying spar urethane on the next one. Finally, allow the final coat to dry and cure for three days.

Alternatively, apply one water-repellent coat and let it dry as the manufacturer instructs. Further, the wood will take time to dry if it has been dip treated. This process also helps you to waterproof your cedar.

Here’s How to Weatherproof Cedar:

What Oils Can You Use On Cedar Wood Outdoors?

Oiling cedar wood helps to waterproof it while enhancing its beauty. Although linseed oil is popular and the most recommended, Danish, teak and Tung oil can also be used on cedar with excellent results. Let’s have a look at them in detail.

  • Linseed Oil

The formula comes from the linseed-flax plant.

This type of oil is not only popular. But it’s also the most preferred natural finish for cedar since it’s easy to apply. Besides, it enhances the beauty of cedar and increases its durability.

There are many linseed oils, but boiled and raw are the most common.

Boiled linseed oil is processed by passing hot air to fasten the drying process. The oil flows inside the wood’s pores, producing a durable wood finish.

On the other hand, raw linseed oil remains the same without thinners or driers and takes time to dry. It is usually applied on cricket bats to protect them from moisture, splitting, or cracking.

Even more important, linseed oil seeps inside cedar and hardens, making the wood strong inside and outside. However, you may need to apply a finish that has UV inhibitors if you are using it for exterior projects to protect your cedar from fading caused by UV rays from the sun.

Generally, linseed oil can be applied on stains, but that will depend on the type of wood stain. Use non-grain raising or water stains since solvent-based interferes with the oil’s penetration. Compared to other oil finishes, linseed oil takes a long time to dry but enhances cedar’s beautiful look at the end.

  • Teak Oil

While there is a misconception that this type of oil comes from teak wood, teak oil is a mixture of Tung oil, linseed oil varnish, mineral spirits, varnish, etc. (depending on the type of brand). Although it was produced to be used on teak wood, it still works on cedar enhancing its color and grain pattern.

Like boiled linseed oil, teak oil isn’t waterproof, doesn’t provide durability, and may need to be applied annually. Although it contains UV inhibitors that can protect the wood from UV rays compared to boiled linseed oil, that’s not much of an advantage as it wears off faster.

Using teak oil on the exterior cedar doesn’t guarantee it is weatherproof. But if you plan to use it on exterior cedar or live in high-humidity areas, maintain it regularly.

  • Tung Oil

It’s also known as china wood oil, made from the seeds and nuts of a Tung tree. It turns hard and solid when placed at room temperature, making it suitable for waterproofing. It gives a fresh wet appearance on the cedar surface after curing.

Use pure Tung oil since it’s pure from added preservatives.

Apply 5- 6 coats of Tung oil on the cedar to waterproof and protect it from weather elements. Let each coat dry before applying the next one, and let it cure for two weeks to achieve an excellent finish.

However, it contains unsafe solvents and additives for humans and the environment.

  • Danish Oil

Danish oil is obtained from a mixture of varnish, resins, and natural oils, and applying it to cedar increases its durability by protecting the wood from harsh weather. It also highlights the wood’s grain and appearance without altering the color of the cedar.

The best part is it’s easy to apply and takes less time to dry than linseed oil.

How to Oil Cedar

  •  Preparation

Using super-fine grit sandpaper, sand carefully along the direction of the wood grain. Wipe the wood with a clean rag to remove dust.

  •  Apply the First Coat of Oil

Ensure you are in a well-ventilated place. Use a rag or brush to apply the oil (of your choice) either pour the oil on the cedar or pour it on the rag you are using to apply. The oil should be generously applied and left to soak for 10 – 30 minutes before wiping off any excess oil using a clean rag.

Ensure the oil is evenly applied without missing any spots and in the direction of the grain. Let the first coat dry before moving to the next step.

Note: Avoid wadding up oil-soaked rags or putting them in the trash. Instead, spread them on a drop cloth or newspaper. 

Linseed or teak oil-soaked cloths should be dry before being disposed of. Disposing of the rags in ball form can cause them to light up on their own.

Sometimes oil raises the wood grain roughening the texture; sand lightly to smoothen your surface

  •  Apply the Second Coat

The second coat should not be liberally applied since the first coat might have slightly soaked the wood and won’t be able to retake a significant amount. Pour a small amount of oil on the rag or surface, then spread it on the whole surface without missing a spot. Wait for 15 to 30 minutes before wiping off excess oil to allow it to dry faster.

Repeat the process until you are satisfied with the look, though the wood may get soaked up and won’t absorb oil anymore.

  •  Wiping Off Excess Oil

At some point, the wood may become saturated and leak some out. Just use a clean rag to wipe it off once or twice; otherwise, it may prevent it from drying properly and become sticky, ruining the texture.

Oil should be re-applied at least once a year.

Can You Clear Coat Cedar?

Absolutely yes! Cedar can be clear coated but works better indoors than outdoors since it is not subjected to weather elements such as UV rays, rain, snow, mold, insects, and algae, which causes wood deterioration.

Even though they’ll work remarkably well outdoors, there is still the risk of wearing out faster than paint finishes and solid stains. Clear coats enhance cedar’s natural beauty by making the wood grain and color visible, but they still deteriorate over time.

Contrarily, even though solid transparent stains conceal cedar’s natural color, they still allow the grain to shine and last longer than clear stains. In addition, the paint lasts long on surfaces despite covering the wood grain.

Apply two coats of transparent stain on cedar wood; the first coat is a sealant to protect your wood from weather elements.

You can clear coat your cedar with transparent, solid, or shellac paints depending on your needs and preferences. Check on their pros and cons before making your decision.


Spar urethane functions exquisitely on cedar by forming a protective coat that protects cedar from UV rays, insect attacks, moisture, dents, and cracks. Furthermore, it highlights the natural grain of cedar, thus enhancing its appearance. In general, spar urethane can also be used on indoor projects, but it’s best for protecting outdoor projects from extreme weather conditions.

On the other hand, cedar has different characteristics that make it the best for outdoor projects such as siding and decking. But still, treating and oiling it can prolong its functions, enhancing its appearance.

Then again,

Can You Use Spar Urethane on Cedar Wood?

In conclusion, spar urethane is the best finish for cedar, especially if you follow the correct procedure, as discussed earlier. Oil-based spar urethane takes time to dry; let it dry completely before adding the next coat.

Finally, spar urethane is vulnerable to alcohol and chemicals, as using them to clean your finish can degrade them.

Thank you for reading the article. I hope it has clarified everything about spar urethane on cedar.

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