Sanding Sealer Vs Polyurethane (Expert Advise)

If you are looking to finish your wooden structure, there’s always a formula to give it that attractive final coat. In most cases, woodworkers use polyurethane, sanding sealer, or epoxy resin. In this article, I’m going to discuss sanding sealer vs polyurethane. Which one is the best? Which one should you go for depending on the wood you are using?

Keep reading to find out more:

What Is a Wood Sealer?

A wood sealer is a thin formula that gives the lumber a protection layer to prevent damage. It also effectively blocks the wood pores from alterations due to chemical reactions and moisture. Hence, the surface remains intact for an extended duration.

On top of that, the product keeps the wood grain from rising, delivering a smooth surface for consequent coats of finish. In addition, wood sealers add depth of color to the wood and facilitate a professional outcome.

 What Is a Sanding Sealer?

A sanding sealer is a liquid base finish for natural raw lumber and uncoated wood products. Further, it seals the wood and improves the condition of other stain or paint coats and any clear finishes. Thus, the final coat can spread over the surface without soaking into the wood.

Sanding the sealer before adding the topcoat facilitates a smooth, color-consistent finish. Fortunately, the formula only needs one hour to dry, allowing you to complete the work within no time.

On top of that, sanding sealers have zinc stearate as the active ingredient. It provides a soap-like consistency and makes the lacquer fluffier to fill the lumber pores faster. So, you can expect a consistent film on the wood’s surface after sanding.

Please note that sanding sealers are not mandatory if you have softwood and aim for a natural, raw, or unpolished look. They only work to fill wood pores, only found in hardwood.

In addition, hardwoods, like poplar, cedar, and spruce, have many deep pores that absorb any finish. Hence, you’d need more material and time to get full coverage. And worse still, the outcome can often be uneven and blotchy.

Nonetheless, sanding sealers come in handy to fill up wood pores, smooth out the lumber’s surface, and encourage uniform stain absorption. We can also say that they serve as grain fillers which help even out wood surfaces. However, grain fillers are hard to sand away, leaving sanding sealers a perfect option for a convenient woodworking session.

What Is Polyurethane?

Image of a fast drying polyurethanePolyurethane is a protective lumber coating that works on bare wood or over paint or stain finishes. In addition, it delivers excellent protection against multiple kinds of damage from denting, scraping, mildew, fungus, scratching, and pests. Thus, you can enjoy a long-lasting surface.

Additionally, you can use multiple strategies to apply polyurethane formulas. Brushes and rollers are the most common techniques, but you can also utilize a spray applicator for faster and consistent results.

It would be best to apply the product in thin and even coats to avoid delivering a plasticky appearance. Also, remember to tip off the surface or lightly brush it to pop air bubbles. This way, it will dry to a smooth, even finish.

In addition, polyurethane dries to a clear, hard, and water-like finish. Hence, it delivers a beautiful surface. Even better, depending on the product’s formulation, it can be UV-resistant and keep the wood from fading or discoloring.

The first stage of polyurethane hardening occurs when solvents evaporate, leaving a solid surface. Then, the finish continues to cure over the next 20 to 30 days as it interacts with the atmosphere. So, it would be prudent to give the surface enough time to dry.

On top of that, the formula is perfect for high-use surfaces, such as hardwood floors, and is available in multiple sheens ranging from high-gloss to fairly matte. However, it is advisable to sand in between coats to promote good adhesion.

Finally, polyurethane is available in two formulations; Water-based and oil-based polyurethane. Water-based polyurethane emits lower VOC levels and dries in as little as two hours, whereas oil-based formulas off-gas significant VOCs amounts and require up to 24 hours to dry to the touch.

Sanding Sealer Vs Polyurethane Comparison

The final finish is what helps judge the success of any woodworking project. Moreover, no matter how well you measure, cut, carve, and join the wood, it will not yield an excellent result without proper topcoat application.

In addition, you may have to choose between polyurethane or a sanding sealer and a complimentary finish depending on your project needs. Therefore, it is best to learn about these products to choose the best.

Also, note that sanding sealers and polyurethane do not perform the same function. So, check out the following comparison for more clarification.

  • Adhesion

This aspect is a common difference area between polyurethane and a sanding sealer. You can keep going until you get a satisfactory outcome when working with a polyurethane formula. But the story is different for a sanding sealer as you need a different finish for the surface.

Generally, sanding sealers cannot be the final finish for the wood as they only prepare the surface for the topcoat. And you can only expect an ideal outcome after using a compatible finish.

Besides, it is okay to apply lacquer over a sanding sealer consisting of zinc stearate and lacquer. Also, please note that the sealers may not work well with other formulas, and you are safer following the manufacturer’s recommendations.

Unfortunately, the above requirement limits creativity and experimentation. In addition, you would be at a loss if you had already bought the sanding sealer before determining what finish to use.

Oppositely, you will not have these problems with polyurethane because all you need to do is apply more formula for the topcoat. Sand in between coats to help the finish adhere well to the surface. And you will enjoy a cheaper and faster working session while delivering a professional outcome.

  • Level of Finish

The main objective for applying a sanding sealer is to facilitate a smooth wood finish. And this is a perfect comparison point. Sanding sealers are excellent in ensuring that dewaxed shellac and lacquer level on the surface.

In addition, the formula eliminates the need to sand between lacquer coats by removing raised grains and leveling the final film. So, you won’t have inconsistent coverage, with some areas being thinner than others.

On the other hand, polyurethane is a film coat that settles on the lumber’s surface. Moreover, it does not soak into the wood, and you do not have to stress about an uneven finish. Also, although the product is self-leveling, it would be best to sand in between coats for a perfect finish.

Interestingly, the first polyurethane coat serves the same purpose as the sanding sealer. Hence, both products will deliver a smooth finish in the end. And the difference only comes when the sanding sealer needs a different finish for the work to be complete.

  • Number of Coats Needed

A sanding sealer minimizes the coats needed to deliver a lovely and durable finish. Also, remember that water-based topcoats often raise the wood fibers when used directly on stained or unstained lumber. Thus, it would be best to sand the surface before applying the next coat.

Please consider repeating the sanding and application process till you deliver a fine texture. Fortunately, although the sanding sealer raises the wood grain, the job is complete once you sand the first coat and apply the next one. So, you do not need multiple layers for your work.

Conversely, polyurethane formulas work entirely differently. The water-based formulas will always raise the wood grain, requiring you to apply multiple coats. You may even need to have seven coats of the product on a table to deliver the perfect texture.

But before you dismiss the product, oil-based polyurethane does not have this problem. All you need is two to three coats to get an excellent finish after sanding the bare wood. In addition, you will use fewer coats with polyurethane than if you had a sanding sealer.

Lastly, note that a sanding sealer considerably reduces the number of paint or stain coats you need for your work. Therefore, it is best to determine the most suitable product for impressive results.

  • Drying Time

The number of coats prompts us also to consider the duration a product needs for each coat to dry. For instance, lacquer is among the fastest drying formulas as you apply it in multiple thin coats. So, within an hour, you could be ready to add another layer.

Luckily, sanding sealers reduce the coats needed for a desirable finish and save time. Therefore, depending on the product brand and manufacturer, the formula can be just as fast.

Polyurethane, on the other hand, features a pretty notorious drying time. For example, oil-based products need up to 12 hours before adding the next layer. Worse still, you need to sand in between coats, which consumes more project time.

Even so, you can still save time with water-based polyurethanes as they only need two hours or less to dry. But you are safer checking the product drying specifications and application method for the best finish.

Finally, spraying or wiping polyurethane helps it dry much faster without affecting durability. Therefore, unless you need a specific fast-drying sanding sealer, the faster strategy is water-based polyurethane.

  • Versatility

Sanding sealers can only work on bare wood, and thus it would be prudent to avoid them for finishing applications. Moreover, they prevent the finish from seeping into the wood grain. So, you can only get results on specific surfaces.

Also, the sealer will not adhere to an existing finish, and hence it is unnecessary having it on stained wood. Even worse, it will be a time-consuming step with no apparent results or surface improvement.

Conversely, polyurethane works perfectly on almost any surface. More so, it can adhere to stained, raw, or even finished wood, and you can use it over chalk paint and other painted lumber.

  • Ease of Application

The product’s application strategy is another aspect to consider when comparing these two formulas. However, both products will give satisfactory results with a roller, paintbrush, or sprayer.

You can fully expect a sanding sealer to hold up the topcoat for an extended duration. But you’d have to use a few coats. So, a roller or brush is perfect for the work.

Besides, zinc stearate makes the lacquer soft, and you don’t want to have too much leftover product after the project. Also, remember that lacquer is a pretty hard but brittle finish but can crack or chip if you apply thick coats. Thus, you can consider using a roller or brush to help monitor the coat’s thickness.

On the other hand, polyurethane is among the hardest and most durable formulas, and it does not need too many coats. Also, although you can have as many coats as possible, applying two to three coats won’t affect the coat’s durability.

  • Durability/Longevity

Polyurethane is highly durable, and you can expect it to last between five to ten years. But this duration depends on the exposure level to harmful elements, application technique, and maintenance routine.

Oppositely, sanding sealer is a very soft and non-durable material. Moreover, you can incur severe problems after too much sanding. Even worse, the sealer can crack, slide, or disconnect from the wood’s surface and compromise the finish.

That said, sanding sealers and polyurethane formulas have differentiating factors, requiring you to predetermine your project needs before picking a product. Fortunately, it is easy to distinguish between these two formulas.

Generally, a sanding sealer is often a finishing base that prepares the wood for a topcoat. At the same time, polyurethane comes in handy in the final step when finishing the wood and can work over a sanding sealer.

Does Sanding Sealer Waterproof Wood?

Although a sanding sealer does not waterproof wood, it can help the lumber deal with moisture. Moreover, the product features chemical properties that make it a perfect base layer for the topcoat. This way, the surface is safe from excess water.

Nonetheless, the sealer can only protect the lumber from moisture for a little while. Hence, you are safer not using it as a water-resistant product. Even better, keep the wood away from humidity or use a water-resistant rag over it.

What Can I Use Instead of Sanding Sealer?

You can use shellac instead of a sanding sealer. Although it is not an actual sanding sealer, it accomplishes the same result. In addition, you can dilute it from 2lb to 1lb cut or dry shellac flakes and mix them with denatured alcohol.

Shellac products feature an excellent base for multiple finishes and thus a perfect alternative for most projects. Even better, it enhances adhesion and helps the topcoat adhere tightly to the surface.

Alternatively, you can get finishes with a build-up, such as walnut oil, tung oil, or commercial wood finishing oil. They will act as a sanding sealer since the layers build upon each other and cover the surface.

What Is the Difference Between Grain Filler and Sanding Sealer?

Image of a sanding sealer in the Sanding Sealer Vs Polyurethane comparisonA sanding sealer is suitable for unfinished wood as it raises the wood grain. Then, it gives you an easy sanding time to level and smooth the surface. This way, you can quickly deliver a perfect, ready-to-paint or stain surface.

On the other hand, grain filler does not work on unfinished lumber. Instead, you apply it after working on at least one coat of polish, lacquer, or stain. In addition, the product won’t fill the grain ups, and thus it only works on open-grained lumber.

Unlike sanding sealers, grain fillers do not affect the wood fibers in any way. Therefore, you cannot smooth the surface before applying the finishing product. Also, it does not blend well with polish. Thus, it is prudent to check the manufacturer’s recommended finishing formulas for a successful outcome.

The products have varying application techniques. For instance, a sanding sealer delivers better results after brushing, spraying, or whipping it on the lumber, while a grain filler works best with a coarse cloth, like hessian.

In addition, it would be best to avoid sanding a grain filler as it clogs the sandpaper and removes the fill from the grain. However, you can go ahead and sand a sanding sealer to level the raised wood fibers.

Lastly, a sanding sealer is often transparent and can even work on a stain to deliver a more durable and professional finish. On the other hand, you can stain a wood filler before wiping it on the surface.

Do You Sand After Sanding Sealer?

It is advisable to sand after applying a sanding sealer. However, please wait for the formula to dry before the process. Otherwise, you may end up removing it and compromise the project’s success.

Besides, a sanding sealer raises the wood fibers before sealing the surface. Therefore, it is best to sand the finish to level it and enhance the condition of subsequent clear finish or paint coats.

Frequently Asked Questions

  • Can I Use Polyurethane to Seal Wood?

Yes. It is possible to apply polyurethane as a wood sealant. More so, the formula waterproofs the surface and creates a hard protective coat that withstands water damage and harsh ultraviolet rays.

In addition, polyurethane can act both as a base coat and a finishing layer. The first coat seals the wood pores to facilitate consistent formula absorption, and the subsequent ones enhance durability and texture.

  • Can I Use Sanding Sealer as a Finish?

It is not advisable to use a sanding sealer as a wood finish. The product does not protect the wood from UV light, stains, water, or scratches. Therefore, the finish will fail within no time, leading to wasted resources.

Additionally, wood finishes add an impenetrable protection layer to the lumber and enhance its appearance, which a wood sealer may not hack. So, it is prudent to have a different finish on the sanding sealer, whether lacquer, polyurethane, or shellac.

  • When Should I Use Sanding Sealer?

You can use sanding sealer on bare or natural wood before adding any finish. It will also work on stained wood since its primary purpose is to fill the wood pores and facilitate a level surface.

Also, applying the sealer after a finishing product is redundant. Thus, some wood finish manufacturers discourage using sanding sealers on stained surfaces. But you can consult with your product label to get the specific application instructions.

  • Do I Need to Use Sanding Sealer?

No. You do not need a sanding sealer as manufacturers recommend it for woods with open grains, such as spruce, cedar, walnut, and mahogany. However, it would be wise to talk to a woodworking expert when in doubt.

In addition, you can forego the product for varnish, polyurethane, or spar urethane. But it is okay to use it for lacquer formulas to deliver a smooth and more consistent finish.

  • Is Sealer the Same Thing as Polyurethane?

No, a sealer is not the same product as polyurethane. Sealers are general wood finishes that close the lumber’s pores and protect the wood’s surface from water and pests damage. Also, nothing should penetrate the wood once you apply the sealer.

On top of that, while all polyurethanes can work as sealers, not all sealer formulas are polyurethane products. Therefore, you can use a polyurethane formula to seal the wood and get a successful outcome.


Wood laps up or soaks most formulas applied, poured, or brushed into the surface. Further, porous lumber makes it nearly impossible to deliver a smooth topcoat without first filling their pores. So, it is possible to get a smooth, consistent finish by choosing the most suitable product. Check out the debate below to get more insight into:

Sanding Sealer Vs Polyurethane

A sanding sealer is suitable for bare wood, porous lumber, or when applying lacquer or shellac finishes, whereas polyurethane works best for almost all surfaces. Thus, you can only make a wise decision after determining your product requirements.

In addition, it is okay to use a sanding sealer before applying polyurethane to facilitate a smoother and professional finish. But it is not mandatory since the latter achieves outstanding results on any wood, no matter how porous.

Lastly, you can use polyurethane alone when you do not need multiple coats or sand between coats. Otherwise, a sanding sealer will save you lots of time and coats. So, check out the comparison again and make the best decision!

Image of a woodworker wearing hearing protectors for woodworking

Tyron Otieno

Tyron is an avid woodworker and writer. He founded this website to help other woodworkers, whether hobbyists or professionals by sharing his knowledge and experiencie after a decade of woodworking.

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