Polyurethane is a versatile material that has found its way into many aspects of our daily lives. From the soles of our shoes to the varnish on our wooden furniture, polyurethane is a common sight, though we may not always realize it. Two main types of polyurethane are commonly used – water-based and oil-based. Each has its own set of characteristics that make it suitable for different applications.
Water-based polyurethane is a type of varnish commonly used in woodworking and furniture-making. It’s a clear finish that is known for its fast-drying properties and low odor. Unlike its oil-based counterpart, water-based polyurethane comprises tiny plastic particles suspended in water. When the water evaporates after application, it leaves a clear, protective finish behind.
The main component of water-based polyurethane is acrylic resin, which gives it clarity and fast-drying properties. This type of polyurethane is often chosen for its environmental benefits, as it has a lower volatile organic compound (VOC) content than oil-based polyurethane. This means it’s less environmentally harmful and safer to work with.
Advantages of Water-Based Polyurethane
Before we delve into the disadvantages, it’s important to acknowledge the benefits of water-based polyurethane. This type of finish has several advantages, making it a popular choice among woodworkers and furniture makers.
Firstly, water-based polyurethane dries quickly, often in a matter of hours. This can significantly speed up project timelines, allowing for multiple coats in a single day. Secondly, it has a low odor, making it more pleasant and safer to work with, especially in enclosed spaces.
Moreover, water-based polyurethane is known for its clarity, making it an excellent choice for light-colored woods where you want the natural grain to shine through. Unlike oil-based polyurethane, it doesn’t yellow over time, ensuring the wood’s color remains true for longer.
Finally, water-based polyurethane is environmentally friendly. It has lower VOC content, releasing fewer pollutants into the atmosphere. This makes it a more sustainable choice for those conscious about their environmental impact.
Disadvantages of Water-Based Polyurethane: Cost
Despite its many advantages, water-based polyurethane does come with a few drawbacks. One of the most notable is its cost. Water-based polyurethane tends to be more expensive than oil-based polyurethane. This is due to several factors.
Firstly, the manufacturing process for water-based polyurethane is more complex and costly. The technology used to create tiny plastic particles and to suspend them in water is more advanced than that used in oil-based polyurethane.
Secondly, the raw materials used in water-based polyurethane, particularly acrylic resins, are more expensive. This contributes to the higher overall cost of the product.
Finally, water-based polyurethane is often perceived as a premium product due to its environmental benefits and superior aesthetic qualities. This allows manufacturers to charge a premium price.
Durability
Another disadvantage of water-based polyurethane is its durability. While it provides a hard, protective finish, it’s generally less durable than oil-based polyurethane. This is particularly noticeable in high-traffic areas or surfaces with much use, where the finish may scratch or wear more easily.
Additionally, water-based polyurethane typically requires more coats to achieve the same level of protection as oil-based polyurethane. It has a thinner consistency and doesn’t build up as quickly. While this can result in a smoother finish, it also means more work and a more expensive project, given the higher cost of water-based polyurethane.
Drying Time
While water-based polyurethane is known for its quick drying time, this can also be a disadvantage. The fast drying time means you have less time to work with the finish before it starts to set. This can make applying smoothly challenging, particularly for beginners or those unfamiliar.
Moreover, water-based polyurethane is more susceptible to lap marks because it dries so quickly. These are marks left by the edge of the brush or roller, which can become noticeable when the finish dries. To avoid this, you must maintain a wet edge when applying the finish, which can be difficult, given how quickly it dries.
In contrast, oil-based polyurethane dries more slowly, giving you more time to work with the finish and reducing the risk of lap marks. However, the longer drying time also means you’ll have to wait longer between coats, which can extend the overall project timeline.
Toxicity
While water-based polyurethane is generally considered safer than its oil-based counterpart due to its lower VOC content, it’s not completely free of potentially harmful chemicals.
Some water-based polyurethanes may contain chemicals like isocyanates, which can irritate the eyes, skin, and respiratory tract. Prolonged exposure to these chemicals can lead to more serious health issues, such as asthma or other respiratory problems.
It’s important to note that the toxicity of water-based polyurethane can vary depending on the specific product and manufacturer. Therefore, it’s always a good idea to check the product’s safety data sheet and use appropriate safety measures, such as wearing gloves and a mask and ensuring good ventilation during application and drying.
Appearance
When it comes to the final look of your project, water-based polyurethane may not always be the best choice. While it’s known for its clear finish that doesn’t yellow over time, it doesn’t impart the same depth of color or richness that oil-based polyurethane does.
Oil-based polyurethane has a slight amber hue that can enhance the natural color and grain of the wood, giving it a warm, rich glow. This can be particularly desirable on darker woods or when you want to emphasize the character of the wood.
In contrast, water-based polyurethane provides a clear, “plastic” look that doesn’t alter the color of the wood. While this can be advantageous when working with light-colored woods or wanting a more modern, minimalistic look, it may not be the best choice after a rich, traditional finish.
Environmental Risks
While water-based polyurethane is often touted for its lower environmental impact due to its lower VOC content, it’s not without its environmental risks. One of these is its flammability. While it’s less explosive than oil-based polyurethane, it can still pose a fire risk, particularly during application or if improperly stored.
Additionally, the production process for water-based polyurethane can have environmental impacts. The extraction and processing of raw materials, particularly acrylic resins, can contribute to pollution and resource depletion.
Furthermore, water-based polyurethane is less harmful to the environment when disposed of than oil-based polyurethane, but it’s still not completely benign. It should be disposed of properly to minimize its environmental impact.
Alternatives to Water-Based Polyurethane
If the disadvantages of water-based polyurethane outweigh the benefits for your particular project, there are several alternatives you can consider.
Oil-based polyurethane has its own drawbacks and is a popular choice for its durability, rich finish, and ease of application. It’s particularly well-suited to high-traffic areas and surfaces that use a lot.
Shellac is another option. It’s a natural, non-toxic product with a beautiful, warm finish. However, it’s less durable than polyurethane and can be sensitive to heat and alcohol.
Lacquer is a strong, durable finish that dries quickly and gives a high-gloss finish. However, it’s highly flammable and has a high VOC content, requiring good ventilation and appropriate safety measures during application.
Finally, newer, eco-friendly finishes, such as hard wax oils and plant-based varnishes, are on the market. These offer a more sustainable alternative, though they can be more expensive and may not provide the same level of protection as more traditional finishes.
Issues with Water-Based Polyurethane in Real-Life Applications
In real-world applications, the disadvantages of water-based polyurethane can become quite apparent. For instance, a furniture restorer working on a vintage oak table might choose water-based polyurethane for its clear finish to highlight the wood’s natural grain.
However, despite applying several coats, they soon find the finish scratches easily. This results in a less-than-perfect finish and a disappointed client.
In another case, a homeowner uses water-based polyurethane to finish their hardwood floors, attracted by its low odor and quick drying time. However, the finish isn’t as durable as they’d hoped. Despite careful application and allowing plenty of time for curing, the finish starts to show signs of wear and tear within a few months, particularly in high-traffic areas.
These real-life examples highlight some issues when using water-based polyurethane, particularly regarding durability and the required coats.
Expert Opinions on Water-Based Polyurethane
Many woodworking and furniture restoration experts have weighed in on water-based polyurethane’s disadvantages. Renowned furniture restorer and author Bob Flexner, for instance, has noted that while water-based polyurethane has its place, it’s not always the best choice. He points out that it can be more difficult to apply smoothly due to its quick drying time and that it doesn’t provide the same depth of finish as oil-based polyurethane.
Similarly, woodworking expert and author Michael Dresdner has noted that while water-based polyurethane is a good choice for certain applications, it’s not as durable as oil-based polyurethane and can be more susceptible to water damage.
How to Mitigate the Disadvantages of Water-Based Polyurethane
While water-based polyurethane has its disadvantages, there are ways to mitigate these issues and make the most of its benefits. Here are a few tips and tricks to help you overcome some of the common challenges associated with water-based polyurethane:
- Apply Multiple Coats: Since water-based polyurethane is thinner and less durable than oil-based, applying multiple coats can help build up a stronger, more protective finish. Just make sure to sand between coats to ensure good adhesion lightly.
- Use a High-Quality Brush: A high-quality, synthetic brush can help you apply the finish more smoothly and reduce the risk of brush marks. Remember to maintain a wet edge to avoid lap marks.
- Seal the Wood First: Water-based polyurethane can raise the grain of the wood, resulting in a rough finish. To prevent this, seal the wood first with a coat of de-waxed shellac or a pre-stain wood conditioner.
- Protect the Finish: To enhance the durability of the finish, consider applying a protective wax or topcoat. This can help protect the finish from scratches and wear.
- Follow Safety Measures: Even though water-based polyurethane is less toxic than oil-based, it’s still important to use it safely. Wear gloves and a mask, ensure good ventilation, and properly dispose of any rags or brushes to prevent fire risks.
FAQs
Is water-based polyurethane better than oil-based?
Whether water-based polyurethane is better than oil-based largely depends on the specific needs of your project; water-based polyurethane is known for its quick drying time, low odor, and clear finish that doesn’t yellow over time. However, it’s generally less durable than oil-based polyurethane, requires more coats, and is more expensive.
Should I use water-based polyurethane?
Water-based polyurethane can be a good choice if you’re working with light-colored woods, want a clear finish that doesn’t yellow, or want a more environmentally friendly option. However, if durability, cost, and a rich, warm finish are your main concerns, you might be better off with oil-based polyurethane.
Can I apply water-based polyurethane over oil-based?
Yes, you can apply water-based polyurethane over an oil-based stain as long as the stain is completely dry. However, applying water-based polyurethane over oil-based polyurethane can result in adhesion issues, so it’s generally not recommended.
Conclusion
Water-based polyurethane is popular for many woodworking and furniture projects due to its quick drying time, low odor, and clear, non-yellowing finish. However, it’s not without its disadvantages. It’s generally less durable than oil-based polyurethane, requires more coats, and is more expensive. It also has potential toxicity and environmental risks, and it doesn’t impart the same depth of color or richness as oil-based polyurethane.
However, by understanding these disadvantages and how to mitigate them, you can make an informed decision about whether water-based polyurethane is the right choice for your project. Remember, the best finish is the one that meets the specific needs of your project and your personal preferences.
