Can’t choose between sanding sealer or polyurethane for your next project? I’ve spent years working with both, and let me tell you, understanding the subtle differences between them can really elevate your craft
So, stick around as I break down the pros and cons of polyurethane vs. sanding sealer, to help you make an informed choice. This is stuff you’ll want to know.
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.
Wood sealers have instructions on the label, so my advice is to 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.
Now, if you’re thinking about using it on stained wood, just don’t. You’ll need to strip off any old paint first, which is a hassle. This formula has unique components, like lacquer and zinc, and you’ll definitely need to sand after applying it. In those instances, I’d recommend a dedicated wood filler instead.
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However, when paired with the right topcoat, a sanding sealer improves your furniture’s quality, appearance, and durability.
The Benefits and Drawbacks of Wood Sealers
Pros
- Additional protection
- Smoother finish
- Preserves natural look
- Perfect for basecoating
- Hydrophobic
Cons
- Compatibility issues
- Unadvisable for topcoating
- Poor filling, patching, and covering capabilities
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.
Now, polyurethane isn’t just confined to the world of woodworking; it’s a jack-of-all-trades. Researchers have played around with its synthetic compounds so much that it’s now used in various crafts, not just for making your favorite coffee table.
In my years of woodworking, I’ve found that a good poly coat can keep furniture looking sharp for well over six years. And don’t even get me started on how versatile it is. You can use it on floors and pretty much any woodwork that needs to stand up to the elements.
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.
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The Benefits and Drawbacks of Polyurethane
Pros
- Durable
- Versatile
- Long-lasting and resilient
- Cost-effective
- Heat, weather, scratch, and moist resistant
- Great polishing agent
Cons
- Toxic
- Flammable
- Rigid or unpatchable if damaged
Comparing Sanding Sealers and Polyurethane
Let’s get into the sanding sealer vs. polyurethane debate as objectively as possible. I’ve weighed these options many times over the years, so let’s get down to the nitty-gritty.
First off, don’t just go by the scorecard. Just because one gets more ticks on your list doesn’t make it the end-all, be-all. It’s really about what you’re aiming to get out of your woodwork.
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.
Water-based polyurethane (assuming it’s not paired with a basecoat or primer) requires even more coats. I’ve found that four to five applications can give a smoother result. It’s a bit thinner than its oil-based counterpart, so skimping on coats just won’t cut it.
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. But if you’re looking to minimize the number of layers, sanding sealer is definitely a strong contender.
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. In my experience, that’s pretty accurate.
The base layer can be re-coated after 30 minutes. Although you could technically sand and add another layer after another half-hour, I usually like to play it safe and wait at least 1 hour before re-coating. And before applying any topcoat, I give it another 1-2 hours just to be sure it’s fully hardened.
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. In practice, I find that wood coated with oil-based poly is usually ready for light use in about two days, but it’ll need up to 30 days to fully cure.
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.
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, I don’t recommend 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. Sanding sealer is really made for that first coat, and if you’re smart about pairing it with the right topcoat, like shellac for example, the results can be fantastic. Shellac dries quickly, hardens fast, and enhances the wood’s natural beauty.
(But how about dewaxed shellac? Read this informative article next!)
In my experience, certain types of wood, like spruce, which is incredibly porous, can make sanding sealer an invaluable step. 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.
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!
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.
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.
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.
While sanding sealer can provide some level of protection and enhancement to the wood’s appearance, it is often followed by additional coats of varnish, lacquer, or another desired finish for a more durable and aesthetically pleasing result.
If you want harder topcoat, I would 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.
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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
After deep diving into this sealer vs. polyurethane comparison, it’s clear that each has its own merits.
Sanding sealer is your go-to if you’re up against moisture and stains. And 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.
You've probably seen his down-to-earth wisdom in USA Today, Bobvila, Family Handyman, and The Spruce, where he has shared commentary and guidance on various woodworking topics.
Robert is the brain behind Sawinery, where he aims to share tips, tricks, and a passion for all things carpentry.
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