Spar Varnish or Spar Urethane? Which Is the Best Option?

Spar varnish and spar urethane are very different products. The primary difference between them is that spar varnish eventually chalks and chips off, whereas spar urethane maintains a hard and shiny finish. In addition, spar urethane is more of a protective sealant, and spar varnish is a finishing product. But woodworkers would like to compare the two in a Spar Varnish or Spar Urethane debate to get more clarity.

Both spar varnish and spar urethane are perfect in their respective applications. Also, they come in multiple colors to accommodate multiple projects. However, the formulas vary significantly in their application recommendations. For instance, it would be best to apply spar varnish with a soft bristle brush and give it a minimum of 24 hours between coats.

On the other hand, spar urethane works best with a household paintbrush and needs a 30 minutes drying time between coats. Therefore, it would be best to know your project needs and choose the best product. Also, please read through this article for more insight into the two products.

Can You Use Spar Urethane Over Spar Varnish?

It is not a good idea to apply spar urethane over spar varnish. Spar varnish is more elastic, and it works best outside in the weather. Thus, the varnish will not breathe when you cover it with spar urethane. And ultimately, it will crack because it does not take in air at the same rate as urethane.

It would be best to assess the products separately to see how best to use them. This way, you’ll know what to do to deliver a successful product.

• Spar Urethane

Spar urethane is a spar varnish that has plastic urethane as its resin. It is common in exterior woodworking applications. Also, the finish gives a yellow hue because of the high resin content. Therefore, the formula is not suitable for indoor applications.

In addition, the formula is ideal for finishing woodworks that are susceptible to water content like bar tops. Even better, it contains UV blockers that reduce the sun’s fading and graying effects.

This urethane offers a protective barrier against rain and moisture. Also, it has special oils that allow the surface to contract and expand with the lumber as temperatures and seasons change.

On top of that, you can use the product on windows, bathroom cabinets, outdoor furniture, doors, trim, kitchen countertops, and doors. Better still, it gives a crystal clear finish over light-colored woods and stains.

Lastly, spar urethane dries pretty fast and cleans up with warm water. Therefore, it is easy and affordable to apply and maintain.

• Spar Varnish

Spar varnish is a wood finishing varnish. It is mostly suitable for coating the spars of sailing vessels, such as ships. But woodworkers now use it to finish various wooden projects, like garage doors, outdoor wooden bar tops, and furniture.

In addition, the product is an excellent waterproof finish and outdoor wood sealer. It contains phenolic resins and premium tung oil for a warm, beautiful, and transparent amber finish. Therefore, you can use it on all types of exterior and interior wood.

You can recoat the surface in one hour. Hence, you will not have a problem applying the recommended three coats in one day. Even better, the cured varnish remains flexible, contracts, and expands with the wood during temperature changes and seasonal humidity.

The varnish allows you to deliver a gloss or satin finish. Apply four to six coats of gleam gloss to deliver a high gloss finish. Then, build with gleam gloss varnish to get a sleek satin surface. Also, you can use gleam satin for the final layer.

On top of that, spar varnish has multiple uses apart from finishing wood surfaces. It protects the wood from UV rays damage and water. The formula also gives the wood a rustic and authentic look.

That said, it is possible to think that spar urethane and spar varnish are similar products or have no differences. Well, there are some slight differences. For example, spar urethane takes more time to set than spar varnish.

Also, spar urethane has a higher resin content than spar varnish. Hence, it would be best to avoid using it inside the house or for interior wood projects. Otherwise, the yellow hue the formula produces will pose a health hazard.

Spar urethane is synthetic, and you can use it as a water-base or an oil-base. In addition, the formula is more long-lasting and does not need frequent application. On the contrary, spar varnish requires a frequent application and is less pricey.

What Is the Difference Between Varnish and Spar Varnish?

A regular varnish product contains little, if any, ultraviolet blocking additives. Hence, it is a poor choice for exterior woodworking projects. Even worse, standard varnishes and wood go as far as failing without UV protection.

On the other hand, spar varnish features UV rays blockers that keep the surface from fading. In addition, it is waterproof and seals the surface. Therefore, you can expect a long-lasting finish.

What Is the Difference Between Spar Urethane and Polyurethane?

Spar urethane features a density of 0.9 g/cm^3. It is suitable for surfboard production and snowsports, thanks to its excellent abrasion resistance. On the other hand, polyurethanes are common for construction materials like insulation substances, adhesives, sealants, coatings, and packaging.

In addition, polyurethanes are perfect for making boat hulls, club heads, and multiple industrial applications. You will also benefit from the four types of finishes it delivers. They include satin, matte, semi-gloss, and high gloss.

In fewer words, spar urethane is durable, tough, and resists harsh weather conditions, whereas polyurethane is more sensitive and flexible.

Can Urethane be Applied Over Varnish?

Yes, it is okay to apply urethane over varnish without ruining the finish. The formula is long-lasting, hard-wearing, and with a high resin value. Therefore, it can withstand extreme outdoor conditions.

However, it would be wise to pay attention to the product types. Some kinds of polyurethane and varnish do not work well with some wood types. Also, check out the following tips to deliver a sophisticated finish.

First, choose the most suitable application strategy. Fortunately, we have three ways you can adopt when applying polyurethane over varnish. They include using a roller, a brush, or a sprayer.

Next, get the correct supplies such as shop vacuum, tack-cloth, sanding block, oil-based or water-based polyurethane, wet or dry sandpaper, 80-, 120-, 180-, 220-, grit sandpaper, mineral spirits, automotive polishing compound, quality brush, automotive rubbing compound, and distilled water for water-based polyurethane.

Finally, follow the detailed procedure below.

• Sand the Wood

Preparing a surface to receive a sealant is never only cosmetic. Carefully shaping and sanding the wood get you the most even fit with fewer bumps. In addition, the finish will look much better, age gracefully, and simplify future refinishing projects.

Check the wood for streaks or unevenness. This way, you’ll know the specific areas to focus on to deliver clean and polished wood. Also, you will get a smooth and uniform color throughout the entire surface after going through basic preparation guidelines.

• Remove the Dust

Use a vacuum cleaner to dust the surface. Otherwise, wood may start looking dingy, rotten, or fuzzy. In addition, you can get a shop vacuum with a soft brush attachment for the hard-to-reach areas.

On top of that, it is better to dip a clean, lint-free cloth in mineral spirits to handle stubborn stains. Also, ensure that you remove all the wax and grease by scrubbing the wood. This way, the paint will not have a hard time adhering to the surface. 

• Seal the Surface

An oil-based polyurethane product is the best sealer for your wood project. It extends the lumber’s life and protects it from stains and water damage. More so, you are good to go with only one or two coats.

Here, it is prudent to thin the oil-based formula using one part of mineral spirits and two parts of polyurethane. Also, please use a flat stir stick to stir the mixture before applying it to the surface.

On top of that, it would be best to avoid shaking the can or using an exploded tip synthetic brush. Otherwise, the divided strands may introduce air bubbles in the polyurethane formula.

Lastly, use long and even strokes from one end to another. This way, you will deliver full coverage and get uniform and consistent coats. Also, wait for about 24 hours for the finish to dry before using it or going to the next step.

• Apply the First Polyurethane Coat

Apply a layer of polyurethane after 24 hours to allow the sealer to dry. This way, you’ll deliver a more durable result. Also, please avoid wiping the brush on the can’s rim, as it will help avoid air bubbles in the paint can.

It would be much better to use water-based polyurethane formula when you want a fast-drying coat. However, you’ll need to apply more layers than you will with an oil-based polyurethane product.

On top of that, remember to spread the spar varnish on the surface before applying the polyurethane. Also, use long and even strokes throughout while overlapping some of them to deliver a uniform coat.

• Shave Off the Bumps

Examine the surface for bumps when the coat dries. Please use a sharp chisel or razor blade to cut any drips. And avoid cutting the drip underneath as it may damage the surrounding surface.

• Wet Sand the First Coat

It would be best to wet sand the surface to remove dust bumps and minor blemishes. In addition, you can get 400-grit sandpaper and mount it to a sanding block for added convenience.

Remember to wipe the surface with a moist cloth after sanding. This way, you’ll clear any dust particles that can compromise a successful outcome.

• Add the Second Coat

Wait for about 24 to 48 hours, then apply the second coat. It would be best to repeat the fourth, fifth, and sixth steps to deliver a more uniform finish. But please be careful not to have any drips on the surface, as you may not be able to remove them.

• Polish the Surface if You Wet-Sanded the Second Coat

Use the automotive rubbing compound to polish the finish. You can also dampen the cloth with water and apply the compound in circular motions. This way, you’ll remove any scratches left by the sandpaper.

On top of that, buff the finish with a clean, dry cloth when the workpiece dries. In addition, it is okay to apply the polishing compound as the final step to get a more excellent surface.

Why Is My Spar Urethane Sticky?

Spar urethane becomes sticky when you do not clean the wood before varnishing. Thus, the first step before applying spar urethane is to wash the wood well using a wax-removing detergent.

In addition, high humidity, poor ventilation, and chemicals in the air like ammonia can compromise the curing process. Therefore, it would be best to work in a well-ventilated space. 

You can run a dehumidifier to reduce the humidity in the air. In addition, please moisten a rag with mineral spirits or turpentine and wipe the varnish lightly. It is also okay to point a fan at the drying varnish.

On top of that, avoid rubbing the varnish as you may ruin it. Instead, wipe it gently enough to remove any tackiness from the surface. Also, give the finish a day or two under the breeze of a fan.

Spray or brush a light layer of clear shellac on the wood if the varnish is still tacky. The formula hardens by evaporation, and thus it does not have to cure. However, it would be best to use shellac when the varnish is almost hard.

Is Spar Urethane Good for Outdoor Furniture?

Yes! Spar urethane is good for outdoor furniture. It delivers a durable waterproof surface and keeps the wood from rotting. Even better, the surface will benefit from a UV-resistant barrier that prevents wood discoloration and fading.

In addition, the product application procedure is quite easy. All you need is a brush, and you are good to go! Better still, spar urethane does not go bad soon, and it can last up to ten to fifteen years.

Can I Use Spar Urethane on a Kitchen Table?

It is okay to use spar urethane on a kitchen table. It does not present any known hazard that would make it unsuitable for kitchen use. However, you are safer when the finish cures well before using it.

The best duration and conditions that assure you full curing is 30 days and room temperatures of about 65- to 75- degrees Fahrenheit. This way, you are sure of a fairly flexible and durable coating. 

How Do I Get a Smooth Finish With Spar Urethane?

It would be realistic to admit that applying spar urethane without bubbles or brush strokes takes a little skill and finesse. Therefore, you need practice and the correct paintbrush to get the technique right.

The easiest strategy to use involves wetting the applicator with a thinner. Then, dip it into the diluted formula. Also, ensure that you overlap the previous stroke by half with each pass. This way, you’ll avoid annoying bubbles and brush strokes.

Sponge brushes are another option for delivering a smooth finish, but the outcome is not always a noticeable improvement. Remember that most of the application trouble comes from the formula being too thick. Thus, painting the surface would be like laying down a uniform coat of corn syrup.

Luckily, you can improve the workability of the spar urethane formula by thinning it with mineral spirits. Thinning it by around 10 to 20 percent will make brushing much easier. Even better, the move will allow you to spray the urethane using HVLP.

Additionally, thinning will help the finish to self-level and eventually help to avoid brush marks. But there is a caveat. You need to apply more layers to achieve the desired film thickness.

Another easy way to use when painting with spar urethane is abandoning all brushes altogether. Thin the varnish 50 percent with mineral spirits, naphtha, or paint thinner. Then, get a clean cotton rag, like old t-shirt material, and fold it into a square applicator.

Wet the applicator with the thinner and soak it into the diluted formula. Next, wipe on smooth layers on the surface. In addition, ensure that you overlap the previous stroke by about a half with each pass.

Even so, remember that it would be best to apply twice as many layers to deliver the nest film thickness. Also, the dry time will decrease because you are applying less formula on the surface.

Therefore, you can apply as many as three urethane layers per day in hot climates. But remember that it would be better to coat the surface evenly using thin wet films instead of flooding on a thick coat.

How Long Does It Take Spar Urethane to Dry?

It takes spar urethane about 24 hours to dry before normal use. However, the duration may go as far as 72 days, depending on the existing environmental conditions. For example, your finish will be dry and ready for use within 24 hours when the weather is fair.

On the other hand, you will have to wait for even three days if there are low temperatures and high humidity levels. Therefore, it would be best to countercheck with the weather forecast before choosing a painting day.

Frequently Asked Questions

• How Long Does Spar Urethane last?

Believe it or not, spar urethane lasts between ten to 15 years. It is among the best formulas for a kayak seat or pad. However, you are safer when you apply the product correctly, or else the finish may collapse sooner than you expected.

Spar urethane helps to protect against splinters and scratches and keeps the surface looking smooth. Better still, it is water-resistant and thus an excellent choice if you use your boat in saltwater. So, it will serve you for a long, long time.

The product features UV inhibitors. Hence, it will not peel or crack as regular paint would after some time. Also, exposure to mildew does not affect the finish, thanks to its mildew prevention agents.

• Do I Need to Sand Between Coats of Spar Urethane?

There’s no need to sand in-between spar urethane coats. The finish will eventually level and smoothen out after drying. Therefore, it will be ready for the next coat without much human interference.

However, sometimes you may apply too much spar urethane, leading to a lot of orange peel. Therefore, you may want to sand in-between coats to guarantee a smooth finish. Also, you may experience an orange peel if you spray the formula too thickly.

Fortunately, you can scrub these imperfections with TSP or a similar heavy-duty detergent. This way, you remove the build-up, and you can re-spray the formula at a lower spray volume before adding another layer.

• Which is Better Oil Based or Water Based Spar Urethane?

Water-based urethanes have water as the main ingredient. Hence, they are safe and do not pose health hazards. On the contrary, oil-based urethanes come from organic solvents and polyol. These compounds are too difficult to remove from clothes, tools, and the skin. Therefore, it would be best to exercise more care when using them.

Conclusion

Spar varnish has natural oil bases like linseed, tung, or soya. It also features UV protectors, resins, and solvents and dries to deliver a shiny finish. Conversely, spar urethane is a synthetic formula that can be oil-based or water-based. The formula is easy to clean, has fewer fumes, and dries within a short duration. Nonetheless, these attributes are overwhelming for each product, which births the debate:

Spar Varnish or Spar Urethane

Spar urethane has a higher moisture protection level than spar varnish. Hence, it is a better choice for the underside of canoes or boats and paddles. It also requires fewer applications and is more durable. So, you’ll find it easy to use, especially if it is your first time working with the formula.

Even so, the choice of which product to use boils down to your budget and how much maintenance you plan on doing. The bottom line is to deliver enough protection to your wood project.