Sanding Sealer vs. Polyurethane: Which Should I Use?

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Can’t choose between sanding sealer or polyurethane for your next project? Experts can identify nuanced differences, and knowing their strengths and weaknesses helps improve your craft. 

For years, our woodworkers use these as topcoats on multiple projects. Scroll down to see our in-depth polyurethane vs. sanding sealer comparison to help you decide! 

About Wood Sealers

By nature, wood absorbs water through its pores, which makes the surface more prone to damage. To avoid this, a wood sealer penetrates the pores, creating a film on the surface that barriers wood against environmental exposure.

Wood sealer is based on oil, water, or latex. Each has its own pros and cons. For example, oil-based is perfect outdoors, and latex is much thicker, while water-based is less toxic and is more water resistant. Just be sure you pick the right one based on wood type and condition.

preparing wood sealer

Wood sealers have instructions on the label, so follow them for best results. Manufacturers sometimes provide recommendations you can pair with wood sealers for your finish. 

One way or the other, all wood sealers bring out natural beauty of your wood and protect it from getting wet.

Must Read: Best Sealers For Your Outdoor Wood Furniture 

About Sanding Sealers

If you check stores online, sanding and wood sealers function similarly. What distinguishes sanding wood is that it’s mainly used as basecoat. 

It’s more effective on bare wood and is specifically formulated to work best on spruce, oak, and other porous trees. They usually dry within an hour.

Ready Seal 512 5-Gallons Pail Natural Cedar Extension Stain and Sealer for Wood

Old paint should be removed before you coat with this formula. That’s why it’s a disadvantage to use on stained wood. It contains ingredients like lacquer and zinc, and the compound requires sanding. In this case, use dedicated wood filler. 

You Might Want to Check Out: Recommended Wood Grain Fillers for Cabinets

However, sanding sealer improves your furniture’s quality, appearance, and durability when paired with the appropriate topcoat.  

The Benefits and Drawbacks of Wood Sealers

Pros

Cons

About Polyurethane

Polyurethane is a polymer blended with urethane for wood coating, sealant, and foam. Its bonding process of components creates a compound capable of resisting high temperatures. It also makes the surface durable, resilient, hard, and quick-drying.

Researchers found synthetic compounds flexible that they tailored for various applications, which is why it’s widely used in the crafting industry outside of woodworking. 

polyurethane products

Poly in woodworking — oil or water-based — is used for furniture coating that lasts for over six years. We can also use it on floors and all kinds of woodwork, even when exposed to external conditions. 

Oil-based poly self-levels when applied to flat surfaces. It’s tougher than water-based, but the color declines over time.

On the other hand, water-based is easier to apply, dries quicker, and is a lot safer. It gives a nice glow and is often smoother when applied properly. 

Read Next

The Benefits and Drawbacks of Polyurethane

Pros

Cons

Comparing Sanding Sealers and Polyurethane

Our team addressed the battle between sanding sealer vs. polyurethane as objectively as possible. We scored our judgment using criteria you needed to know.

sanding polyurethane

Remember, not because the other gets more scores doesn’t mean it’s necessarily what you’re looking for. There are many variables you need to consider, so pick the sealer appropriate for the factors you are looking for in a coat!

Coats Needed

Sanding sealer is made to reduce the number of coatings applied to your wood. It sinks into wood fibers, raising the surface, hence lesser coats. 

Most manufacturers claim you’ll only need not over 2 coats of sanding sealer and at least 2 more layers of topcoats to achieve smooth and silky finish. 

On the contrary, polyurethane depends on its key ingredient. Oil-based is slightly stronger than water-based. 2-3 coatings are enough in an oil-based, but adding 1-2 more is better if it’s without a basecoat. 

applying wood sealer

Water-based polyurethane (assuming it’s not paired with a basecoat or primer) requires even more coats. The good thing is it gets smoother if applied 4-5 times. It’s thinner than oil-based, and any less than the required number of coats won’t be enough.

However, sanding sealer doesn’t work well as a standalone. So the quality of the topcoat paired with it largely affects the number of coats needed. Nonetheless, lesser coating is its best attribute. 

Winner: Sanding Sealer

Drying or Curing Time

This next argument’s point is which sealer would make your job quicker. How quickly does the mixture dries? How many coats would it take? And much time the finish needs to settle fully?

Top sanding sealer brands claim their product can help complete your work in a day. 

The base layer can be re-coated after 30 minutes. You can sand and apply next coat after another 30 minutes. But, we usually wait at least 1 hour to be sure, and another 1-2 hours before a topcoat, so it can take enough time to harden completely. 

preparing to sand table with wood sealer before applying second coat

Oil-based and water-based polyurethane is distinct in terms of drying and curing time. 

You can re-coat fast-drying oil-based poly every 4-6 hours. In normal conditions, topcoat touch dries within a day, and hardens even quicker in warm temperatures. Regardless, wood topcoated with poly is ready for light use after 2 days and will fully cure in 30 days. 

Water-based poly significantly dries faster. You can apply the next coat after 1-2 hours. The catch here is that you can’t coat it more than twice in 24 hours, and you have to allow it to cure for 1-2 weeks.  

Winner: Sanding Sealer

Finish

A sanding sealer improves the overall quality of finish. It seals wood from outside exposure, and it’s best applied first, paired with a dedicated topcoat. Instead of sitting on top of the wood surface, it penetrates the fiber. That’s why most sanding sealers are great at leveling your finish. 

However, a sanding sealer is not durable enough as topcoat compared to other alternatives like polyurethane. Oil-based poly, in particular, is hard enough to resist damage better, and still able to bring out natural grains of the wood. 

applying polyurethane to table

Poly is heat resistant as well. It mostly comes in varnish, gloss, semi-gloss, or satin polyurethane resemblance. Either way, poly is a great exterior for your woodwork. 

While a sanding sealer by itself provides smooth texture, it’s unwise to have it as your topcoat. Your wood’s final appearance still depends on what kind of topcoat you pair it with.

Winner: Polyurethane

Adhesive Strength

Another crucial factor to consider when comparing polyurethane vs. sanding sealer is how well it adheres to the wood. Presuming you don’t pair sanding sealer with a topcoat, it won’t do much for your wood besides providing barrier between the wood from its environment. 

Sanding sealer sinks into wood fiber, hardening it, and leaving you with thin outer layer. In contrast, polyurethane contains thermoplastic glue and organic chain units. Its formulations and chemical components is what makes poly a quality finish. 

A sanding sealer’s compatibility is the game changer here. We established first coating as its primary purpose. Let’s say you put shellac over it: shellac easily dries, hardens fast, and accentuates natural look of the wood.   

(But how about dewaxed shellac? Read this informative article next!)

can of polyurethane and paint brush

Specific woods like spruce (has extremely porous properties) raises value and effectiveness of sanding sealers. And water-based sanding sealer like Minwax 65700 works great with polyurethane. Pair them together, and you’re golden. 

As standalones, polyurethane wins this category. At the same time, you’d have better adhesion for your sanding sealer if you pick the right combination. 

Winner: Polyurethane

Application

A sanding sealer contains fluffy ingredients like stearate. It smooths the sealer, causing it to occupy the pores and evens the surface easily. That’s why it doesn’t leave stroke lines cause by brush bristles.

In general, water, alcohol, and ammonia can wipe off sanding sealers. You can easily use cloth to wipe off excess sealer, and it’s specially formulated for sanding. 

Mylands Cellulose Sanding Sealer, for example, can also be used as toner. While Zinsser Universal Sanding Sealer adheres to any previously finished wood and works as pre-stain conditioner as well.

sanding sealer

Meanwhile, polyurethane has powerful smell and is flammable, so you must take safety measures. 

Recommended Read: How to Get Polyurethane Off Your Hands 

It is marketed as sprays, but usually in liquid form and applied with a brush, which leaves obvious marks from your stroke. You need proper technique to get rid of it and have flawless finish. 

You can achieve an excellent finish with polyurethane without toner or basecoat, which gives it more edge than sanding sealer. 

For water-based poly, you simply need water and soap to clean up excess fluid and use water as thinning agent. While oil-based poly requires stronger agents like denatured alcohol or mineral spirit [1] to make your life easier.

Polyurethane clearly dominates sanding sealer as a finishing agent as it’s more versatile and universal. Manufacturers formulated modern polyurethanes to dry faster and easier to apply as possible. But can you put polyurethane over chalk paint? Read here!

sanding sealer for wood

However, a  sanding sealer has zinc stearate additive, making it smoother and fluffy. Sanding sealer is not mandatory, but the entire finishing process becomes easier with it. It’s a great basecoat, dries quickly, and smoothens with ease. 

Winner: Sanding Sealer

Flexibility

As mentioned above, polyurethane is clearly more flexible than a sanding sealer. A sanding sealer relies heavily on its topcoat, and each product’s compatibility is limited. 

For instance, lacquer sanding sealer only works well on lacquer. Also, sealers are dedicated to polyurethane, shellac, etc. Which might be ineffective, even pointless, on other topcoats. 

sanding wood with polyurethane finish

A sanding sealer is too specific because its effectiveness varies on the types of wood it applies to, unlike polyurethane, which remains tough and durable, regardless. 

As a chemical substance, polyurethane is universal. It’s marketed in different forms, whether in spray or liquid. And it functions as an adhesive, coating, polished finish, insulation, and sealant. It is even used in appliances and automotive. 

Winner: Polyurethane

Longevity

The shelf life of sanding sealer differs on manufacturer’s quality. But it commonly expires within 3 years, perhaps a bit longer if furniture/woodwork is taken care of properly. And if it’s without a topcoat, its film will eventually crack. 

Under normal circumstances, a polyurethane finish remains strong and fresh for 6 years if it’s oil-based. In comparison, water-based poly protects your wood for at least 3+ years. 

polyurethane application

If you take care of it well, it can last up to a decade. However, the color of oil-based poly becomes yellowish and dull over time. And fully hardened poly becomes too rigid, it will crack when you apply force on the surface. Nonetheless, polyurethane lasts longer. Want the list of the best non-yellowing polys? Check this review!

Winner: Polyurethane

FAQ

When should you use sanding sealer?

You should use sanding sealer when the wood is still uncoated. Sanding sealer hardens wood fiber, which is why it’s best used as base or undercoating for extremely permeable natural wood. 

Manufacturers formulate this type of sealer to be absorbed by the wood. Be mindful of only using it when the surface of the wood is free of stains, dirt, and dust.

Can I use sanding sealer as a finish?

You can use sanding sealer as a finish, and it is intended for woods that’s never been coated. While it doesn’t cover pores and grains, it often functions to harden wood before you put primer. 

However, it’s a thin liquid-based finish. If you want harder topcoat, we recommend something else. A sanding sealer complements lacquer and shellac. 

Can you use sanding sealer under polyurethane?

You can use sanding sealer under polyurethane. Sanding sealer is a great first layer for your finish, while poly is a durable plastic. You’d have durable and quality finish when both sealers are applied correctly. 

Having said that, check whether certain brands recommend poly over sanding sealer to be sure.

Read Next:

Do you always need to use a sanding sealer?

A sanding sealer provides extra layers on your wood finish to protect against damage. Only use it when you want better and stronger finish on top of your primary sealer.

Its main purpose is to serve as the basecoat for natural and never-been-coated wood. Mixing sanding sealer with your finish is unnecessary if your primary coating can get the job done. 

Will polyurethane seal wood?

Polyurethane is a durable plastic used in coating wood, making it perfect for sealing wood. Manufacturers develop poly sealant to toughen as it dries, making it useful for covering holes and cracks. Poly can seal wounds while preserving the natural appearance of your wood. 

Conclusion

In this sanding sealer vs. polyurethane comparison, our woodworkers explained that the former is best in protecting your wood against moisture, stain, and discoloration. 

While both are basically two sides of the same coin, both being wood coatings, poly works on all types of wood and all kinds of circumstances. Its physical toughness and quality is obvious, and its ease of application makes it a popular choice.

Robert Johnson is a woodworker who takes joy in sharing his passion for creating to the rest of the world. His brainchild, Sawinery, allowed him to do so as well as connect with other craftsmen. He has since built an enviable workshop for himself and an equally impressive online accomplishment: an extensive resource site serving old timers and novices alike.
Robert Johnson
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