Last Updated on August 30, 2023 by Ernest Godia
Choosing the right finish is crucial when protecting and enhancing the beauty of wood surfaces. Varnish and polyurethane are popular options offering excellent protection and a polished look.
Both finishes are available in resinous liquid forms and are incredibly durable when dry, with many similarities. However, varnish and polyurethane differ in cost, composition, durability, and application.
This article explores varnish vs polyurethane in terms of their composition, application methods, the advantages they offer, and other crucial aspects.
Understanding the differences between varnish and polyurethane should better equip you to decide better when selecting the ideal finish for your woodworking project.
What is wood varnish?
Varnish is a clear or tinted natural wood coating made from a combination of resins, oils, and solvents. It forms a hard and durable protective layer on the wood surface, resisting moisture, chemicals, and wear.
It forms a thin, glossy film on the wood surface and has a faint amber tint to it.
The varnish remains pretty flexible when dry. It is also highly resistant to weather elements, thanks to its high solids content. These qualities make it an excellent finish for outdoor wood projects like decks, patio furniture, and garden seats.
Varnish is typically applied with a brush and requires multiple coats to achieve the desired finish. It enhances the natural beauty of the wood by adding depth and a glossy or satin sheen.
Varnish pros and cons
Here is a quick look at some of the advantages and disadvantages of varnish over polyurethane.
Pros of varnish
- Varnish has a slightly softer and more flexible finish compared to polyurethane, making it less prone to cracking.
- It is generally easier to repair varnish than polyurethane. You only need to lightly sand the worn, scratched, or damaged areas and apply a fresh coat of varnish. The new coat can blend seamlessly into the existing finish, making the repair less noticeable.
- Varnish offers a classic, traditional glossy appearance.
- Thanks to its flexibility, varnish is more compatible with softer woods like pine or open-grained woods like oak.
- Varnish tends to maintain the natural appearance of the wood despite imparting a warm, amber hue that can enhance the wood’s natural color and grain.
- Varnish can do a better job of providing a deeper and more pronounced finish than polyurethane. Its multiple coats build up to create a thick layer, adding depth and dimension to the wood surface.
- There are specialized varnishes available that cater to specific needs or effects, like marine varnishes for excellent water resistance, spar varnishes for outdoor applications, and tinted varnishes that can add color to the wood surface while providing protection.
Cons of varnish
- Varnish typically has a longer drying time than many other finishes, including water-based poly.
- Varnish forms extremely thin coats, so you must apply multiple coats to achieve the desired protection.
- The finish imparts an amber tint to wood and may turn yellow over time.
- Varnished surfaces are vulnerable to heat damage.
Best Varnish for Wood
Our recommendation of the best varnish for wood is TotalBoat Gleam Marine Spar Varnish. It is primarily formulated for wood surfaces in marine environments or those exposed to salty seawater and harmful chemicals. This special formulation means the product can excel in the harshest environments.
For variety, read out detailed article on the best varnish for wood.
What is polyurethane?
Polyurethane, on the other hand, is a synthetic resin that forms a clear and tough finish when it dries. It offers similar protective properties as varnish but is generally more resistant to scratches, abrasion, and household chemicals.
However, since polyurethane dries into a hard coating, prolonged sun exposure or fluctuating weather conditions may cause it to crack. So, it is best to use polyurethane on indoor wood projects and leave varnish for outdoor projects.
Polyurethane is available in oil-based and water-based formulations, each with its own application and drying characteristics. It can be applied with a brush, roller, or spray, and like varnish, multiple coats are often needed.
Even though polyurethane is a liquid plastic, it does not melt due to heat once dry. For this reason, polyurethane is a thermosetting polymer.
Polyurethane pros and cons
The following are some leading advantages and disadvantages of polyurethane over varnish.
Pros of poly
- Polyurethane is known for its exceptional durability. It can withstand heavy use, abrasion, and impact.
- Polyurethane is highly versatile. You can use it on a wide range of wood types and non-wood surfaces, and it is available in various sheens.
- Water-based polyurethane dries faster than varnish and cleans up easily with water.
- Water-based polyurethane has lower levels of volatile organic compounds (VOCs)
- Polyurethane offers good heat resistance, which means it can withstand hot objects without leaving marks or causing the finish to blister. This can be advantageous in applications such as tabletops or kitchen countertops where exposure to hot items is common.
- Polyurethane offers good resistance to various chemicals, including household cleaners, oils, and solvents.
- It is generally low-maintenance once dry.
- It is highly compatible with different finishes. It adheres well to a wide range of wood stains, dyes, and finishes, allowing for more flexibility in achieving the desired aesthetic.
Cons of polyurethane
- Polyurethane takes a long time to fully cure and reach its maximum hardness, even though it may dry faster than varnish.
- It requires some elbow grease for proper surface preparation when recoating.
- It is less flexible than varnish, making it more likely to crack in volatile or outdoor environments.
- Oil-based poly is more toxic than varnish.
Best Polyurethane for Wood
Our recommendation of the best polyurethane for wood is Minwax Wipe-On Poly. The product has a thinner consistency than its brush-on cousins. This formulation allows it to seep into wood pores the same way penetrating oil would, except it soon hardens and bonds with the wood’s structure. This way, it offers ultimate wood protection right from within.
What is the difference between varnish and polyurethane?
Varnish is an older, natural coating product made from a combination of resins, oils, and solvents. On the other hand, polyurethane is a water- or oil-based synthetic resin. Varnishes are naturally glossy finishes, but manufacturers also provide non-glossy or flat sheens by tweaking the formulas. Polyurethane, however, is naturally available in a wide range of sheens.
- Different types and brands of varnish and polyurethane are available, and the specific characteristics may vary depending on the brand.
- Personal preferences, the desired appearance, the specific project requirements, and the characteristics of the wood being finished can influence the choice between varnish and polyurethane.
Varnish Vs Polyurethane Head-to-Head Comparison
This section provides a detailed look at the differences between polyurethane and varnishes to help make choosing between them easier.
1. Varnish vs Polyurethane: Composition
Varnish is typically made from a combination of drying oils, resins, and solvents. It forms a hard, transparent film when it dries.
On the other hand, polyurethane is a synthetic product made from polymers. It can be water-based or oil-based. Because it is a synthetic resin, polyurethane, abbreviated as PU, can be termed a liquid plastic.
2. Application and Ease of Use
Varnish is traditionally applied using a brush, and it requires several coats to build up a durable finish because it goes on very thin. This brushing method can appeal to individuals who appreciate the craftsmanship involved in applying a wood finish by hand.
Polyurethane is also applied with a brush, a sprayer, or even a rag. The product is available in traditional brush-on forms and spray forms, making applying an even coat easier.
If you need to apply an additional coat or refresh the finish, varnish requires some surface preparation, such as sanding or stripping, to ensure proper adhesion between layers. The same rule applies to oil-based polyurethane.
Water-based polyurethane, on the other hand, often allows for easier recoating without extensive surface preparation.
3. Drying Time of Varnish vs Polyurethane
Varnish tends to have a longer drying time compared to polyurethane. Depending on the environmental conditions, varnish can take several hours or even days to dry completely.
Polyurethane, especially the water-based variant, typically dries faster, often within a few hours. This makes polyurethane a more suitable choice for users with limited time for their wood-finishing project.
4. Polyurethane vs Varnish: Sheen
Varnishes are naturally glossy finishes, but manufacturers also provide non-glossy or flat sheens by tweaking the formulas. Polyurethane, however, is naturally available in a wide range of sheens.
Polyurethane is available in various sheen options—gloss, semi-gloss, satin, and matte.
5. Durability of Varnish vs Polyurethane
Both varnish and polyurethane offer good durability and protection against scratches, moisture, and UV damage.
However, polyurethane is generally considered to be more durable and resistant to wear and tear, making it suitable for high-traffic areas.
6. Polyurethane vs Varnish for Table Top: Maintenance
Varnish can require more maintenance over time. It may develop a yellowish hue or become brittle with age, necessitating periodic refinishing.
Polyurethane is known for its long-lasting properties and is often easier to maintain compared to varnished surfaces.
7. Specialty Types
There are specialized varnishes available that cater to specific needs or effects, like marine varnishes for excellent water resistance, spar varnishes for outdoor applications, and tinted varnishes that can add color to the wood surface while providing protection.
This versatility available with varnishes allows for more tailored options depending on the project requirements.
Polyurethane, on the other hand, lacks specialty varieties. However, it is available in water- and oil-based formulations with varying characteristics and prices.
8. Common Uses of Varnish vs Polyurethane
Varnish is commonly used for interior and exterior wood surfaces, such as furniture, cabinetry, doors, and trim. It is especially suitable for outdoor applications due to its relative flexibility, which makes it responsive to changes in wood structure due to weather changes.
Polyurethane is also used for similar applications but is particularly popular for floors and other high-wear surfaces due to its durability.
Additionally, varnish is often favored for softer woods like pine or open-grained woods like oak because it can penetrate the pores and provide a flexible protective layer.
Polyurethane, on the other hand, is suitable for a wide range of wood species, including hardwoods and softer woods, due to its surface-sealing properties.
Both products provide a protective layer that enhances the natural beauty of the wood and can add depth and richness to the color.
9. Varnish vs Polyurethane for Furniture: Flexibility
Varnish dries into a slightly softer and more flexible finish compared to polyurethane. This characteristic allows varnish to expand and contract with the wood as it responds to changes in temperature and humidity.
Polyurethane, on the other hand, is relatively rigid and may be prone to cracking if the wood experiences significant movement.
10. Cost of Varnish vs Polyurethane for Wood
The cost of varnish and polyurethane can vary depending on the brand, quality, and type (oil-based or water-based). Generally, varnish tends to be more affordable compared to polyurethane, especially higher-quality polyurethane products.
However, prices can fluctuate, and it’s advisable to compare specific products and consider their performance and durability when making a purchasing decision.
11. Ease of Repairing Varnish vs Polyurethane Surfaces
Both varnish and polyurethane can be repaired if they become damaged. Minor scratches and blemishes can often be fixed by lightly sanding the affected area and applying a new coat of the respective finish.
However, varnish tends to be easier to repair because it can blend more seamlessly into the existing finish. Consider learning how to remove polyurethane from wood without sanding to lessen the burden when repairing polyurethane surfaces.
12. Heat Resistance
Polyurethane tends to have better heat resistance compared to varnish. It can withstand hot objects like cups or plates without leaving marks or causing the finish to blister.
Varnish may be more prone to heat damage and can develop white rings or marks if exposed to hot items. Placing hot objects directly on the varnished wood surface can cause white rings or marks to appear. It’s important to use coasters or trivets to protect the finish from heat sources.
Both polyurethane and varnish are toxic products. Most varnishes, for instance, contain a carcinogenic compound called benzene. Wood varnishes also have solvents and resins that are poisonous if ingested.
Nonetheless, polyurethane is more toxic than varnish. It has isocyanates, a group of chemicals that emit volatile organic compounds (VOCs), which can cause several health complications when inhaled or ingested.
Thankfully, varnishes and polyurethane finishes become harmless when fully cured. The cure time is often about 30 days for polyurethane.
Tips for Using Polyurethane and Varnish
- Both products have their toxicity levels, so always follow safety guidelines and manufacturer’s instructions when working with varnish or polyurethane, including proper ventilation and protective equipment.
- Always test the finish, whether it is varnish or polyurethane, on a small inconspicuous area or a sample piece of wood before applying it to the entire surface to ensure compatibility and the desired results.
- Always consult with a professional when unsure which product really suits your needs to make more informed decisions.
Which is better, polyurethane or varnish?
The better product between polyurethane and varnish depends on the project. Varnish is ideal for outdoor projects due to its superior protection against the sun’s ultraviolet light and weather damage. On the other hand, polyurethane offers incredible durability for interior projects.
Is varnish more durable than polyurethane?
No, varnish is less durable than polyurethane. However, it is more flexible and versatile, so it will last longer than polyurethane outdoors. Its flexibility and superior weather resistance make it more durable on outdoor wood furniture than polyurethane.
Is varnish the same as polyurethane?
No, varnish and polyurethane are different products. Varnish is a traditional wood finish made from drying oils, resins, and solvents. Polyurethane is a synthetic water-based or oil-based wood finish made from polymers. You can also consider polyurethane a liquid plastic.
Can polyurethane be used as varnish?
Yes, polyurethane can be used as a varnish because both products protect wood surfaces from scratches, UV, water damage, and rot. While polyurethane and varnish may differ in durability on outdoor and indoor projects, they will still provide the same benefits to wood surfaces when used interchangeably.
This quality makes varnish vs polyurethane exterior and interior applications interchangeable.
Varnish Vs Polyurethane: Which Is Better?
There is no straight winner between polyurethane and varnish. Rather, the best choice between these two leading finishes depends on your project.
- When to Use Varnish: Use varnish when finishing outdoor wood projects like decks, deck chairs, patio seats, and other outdoor wood surfaces that do not experience heavy use. Its greater flexibility makes it more resistant to water and UV damage.
- When to Use Polyurethane: Use polyurethane on indoor surfaces that encounter heavy use, such as hardwood floors, bar tops, desktops, and cutting boards.