When looking for a finish to use on wood surfaces, you’ll likely narrow the choice to polyurethane (PU). More specifically, oil-based vs. water-based polyurethane.
Both oil-based and water-based polyurethane give wood a protective coat against UV damage, traffic, and color loss. The major difference is that oil-based PU causes wood to take on an amber hue while water-based dries clear. Oil-based polyurethane also gives off strong toxic odors that can be irritating to people with breathing or skin sensitivities.
For more information on which is best for your project, keep reading to learn about water-based and oil-based polyurethane and what situations are best for each type.
Oil-Based vs. Water-Based Polyurethane: Key Points
Polyurethane varnishes are one of the most common wood finishes due to their ease of use and durability. You can apply a coating of this liquid resin to wood cabinets, floors, and other wooden structures using a paint brush, roller, or spray can.
Polyurethane or liquid plastic varnish (used interchangeably with finish) contains a liquid solvent or thinner with oil or water, mixed with polyurethane resin and drying oil. After applying, the solvents evaporate, leaving behind the polyurethane varnish.
Originally, oil-based polyurethanes were preferable because they provided a more durable and long-lasting coating, up to 10 years. However, modern water-based polyurethanes rival oil-based in performance and exceed oil-based in terms of safety for people, pets, and the environment in general. Plus, they can also last up to 10 years when of high quality; five to six years for poor quality.
What Is Water-Based Polyurethane?
Water-based polyurethane contains no solvent but relies on the water for the base to dissolve and transport the polyurethane resin. Water-based polyurethanes have a 30 to 35% concentration of solids, making it a runnier solution.
Once the water-base is applied to a surface, the water will work with the grain, resulting in a thinner coating. Due to this thinness, you’ll need to use at least three coats to get coverage that’s durable and thick enough for protection.
However, you catch a break with the application, as water evaporates faster than solvent, allowing the layer to dry more quickly, so you can apply multiple coats on the same day. Unlike oil-based polyurethane, there is no limit to the number of layers you can use.
When viewing water-based poly in the can, it will appear a milky white color. However, it goes on and dries clear, resulting in little to no change in color for the coated surface. Plus, this clear coating won’t yellow or darken over time. Water polyurethanes also have little to no volatile organic compounds (VOCs) allowing you to use the space within hours of the final coat drying without harm to pets or people.
- Little to no color – clear finish
- Dries fast
- Low to no odor
- Multiple coats applied same day for faster application job
- Easy to clean up with soap and water
- No limit to the number of coats used
- More expensive
- May look colder instead of having a warm glow
- Can be difficult to get an even coating because layers are too clear to keep track of (marking helps with layering)
- Shows scratches easier
- Requires more coats (3 to 4) due to lower solid concentration
- Recoats are required every two years
What Is Oil-Based Polyurethane?
Polymers with an oil base have minerals and petroleum solvents that dissolve the polys, giving a higher solid concentration of 45% to 50% compared to water-based. The oil-based polymers, though, have an amber hue which changes the color of coated wood.
You can apply oil polyurethanes using a brush or spray form. It requires fewer coatings for the poly to form into a hard protective layer than water-based polys too. Unfortunately, the high solvent count means that oil-based polys produce more noxious fumes, both during application and drying.
The use of a breathing respirator is recommended when working with solvent polys. Since the fumes are bothersome for most and irritating for those with breathing or skin problems, it’s better to leave the area vacated until the poly dries – six to 24 hours.
- Fewer coats required
- Hard protective shell for resistance to scratches and abrasions
- Gives wood warm amber glow
- Less expensive
- Higher solid content, allowing for more protectivity
- Lower maintenance
- 10-year lifespan
- Better protection and coverage
- Self-leveling – smooths out when applied to a horizontal surface
- Long dry times – 6 to 10 hours between coats
- Noxious fumes smell for 12 hours or more after the final coat
- Requires chemicals (paint thinner or mineral spirits) for clean up
- Only one coat is applicable every 6 to 24 hours
- Poly must be dried and sanded before applying a new layer
- Long cure times
What Is the Difference Between Water-Based and Oil-Based Polyurethane?
Although both varnishes are types of polyurethane, there are some significant differences to be aware of. For many people, these product variations affect which type they choose for projects.
Polyurethane is a product that forms a protective layer over a wood surface, but it doesn’t soak down into the wood grain like a stain. The final look you get will depend on the sheen type of the poly, whether the poly has a water or oil base, and the application process. In terms of sheen, you have options for satin, semi-gloss, or high-gloss. The glossier the surface, the more it will show nicks, scratches, and other flaws.
Water-based polyurethanes have minimal to no odors or VOCs, making them safer and friendlier to the people, pets, and the environment. On the other hand, oil-based polys contain strong fumes that can be an irritant to some people.
These fumes are stronger during the application, making it advisable to wear gloves, a face mask, and protective clothing and use proper ventilation. The smell can remain until the poly cures.
Both types of polyurethane form a protective coating on a surface that’s resistant to UV rays, corrosion, marring, water, and scuffs. Oil-based polys have a softer feel, making it easier to get dents and peeling, while water-based are more vulnerable to scratches.
Color is the most distinguishing difference between water-based and oil-based polyurethanes. Water-based looks cloudy white in the can but goes on as a clear coat, enhancing wood grain’s natural beauty. Once it goes and dries, it stays translucent rather than darkening.
Oil-based polys have more of a rich amber or golden hue. This coloring will change the way wood looks, giving it a rich, warm tone. As time passes, this goldenness will intensify and darken and sometimes turn yellow.
Number of Coats
Since water-based polys are thinner, they require more coats to get the same protection that you would get with an oil-based poly. An easy way to remember the proportions is for every one coat of oil-based polyurethane, you’ll need two coats of water-based. However, while you can slap on additional coats when using water-based to make the layer strong and durable, you can’t do the same with oil-based. In addition, the more layers you use with an oil-based poly, the higher risk it will be to chipping, scratching, and sheeting.
Both types of polyurethane offer excellent adhesion, making them versatile for use on multiple types of materials. While water-based polyurethanes will bond to all types of materials – cement, non-ferrous metal, wood, fiberglass, cement, and carbon fiber – oil-based polys can stick to anything except oil. So, when applying multiple coats, it’s necessary to sand the surface in between to create a mechanical bond.
VOCs are of high concern with wood varnishes, not just because of the potential for releasing greenhouse gasses, but more frighteningly, because of the risk of short and long-term health issues. In terms of VOC levels, water offers the safer option, with little to no hazardous chemicals and low VOCs (0 to 450 g/L) compared to the higher potential of no less than 275 g/L up to 550 g/L. The VOCs can be released into the air during application and while curing.
Water-based polys have the lead in dry time, drying two to three times faster than oil. Depending on the brand, you can expect a water-based product to dry in two to four hours. Not only does oil take longer to dry between coatings – 6 to 10 hours – but it also has hazardous additives and flammable solvents. The toxic fumes formed while the solvents evaporate help the resin cure into a hard, impenetrable surface.
Curing time is not the same as drying time, which is crucial to remember when working with polyurethane finishes. While the finish is drying, it converts from a liquid form to its final solid state. Therefore, it can take hours or even days for polys to become dry enough to receive a new coating.
Curing, on the other hand, is how long it takes the polyurethane to reach maximum hardness. The surface can still experience damage until the poly cures completely, like denting, scratching, or gouges. Both water-based and oil-based polyurethane take 30 days to reach full cure.
Once the poly has reached full dryness after its final coat, you can move your furniture back into place. However, you’ll need to wait until the poly’s fully cured before using things that will stick to the floor, like area rugs. You’ll also need to avoid using cleaners or water until cured.
Ease of Use
Water can be more difficult to apply properly without messing up because of how fast it dries, which can cause overlapping lines and bubbles. Once dried, you can’t repair mistakes. It does, however, have a longer pot life, which gives you some leeway on how long you have to apply the poly before it becomes unusable.
Another potential issue occurring with water-based is uneven coatings due to the difficulty of seeing the layers due to the translucence. To reduce this issue, you can mark the end of each coating, so you’ll know where to start with the new stroke.
Oil-based polys are easier to apply for several reasons. First, the amber color makes it easy to track your strokes, so you can get a smooth, even surface. The longer drying time also makes it easier to do repairs if you notice a spot that’s damaged or missed while coating. Plus, the thickness of the poly means it requires fewer coatings. Unfortunately, though, there are some things to note about applying oil-based polyurethanes.
The fumes produced are harmful, making it advisable to wear a respirator mask. Cleanup requires the use of high-odor hydrocarbon solvents like turpentine, paint thinner, mineral spirits which are linked to short and long-term health issues. Additionally, the long drying time means it can take two days or more to complete the application (6 hrs dry time x 3 coat application = 18 hours – not including sanding, prep work, and curing).
The higher solid content of oil-based polys (45% to 50%) means that you get better coverage with fewer coats – two to three – compared to the lower solid content of water-based polys (30% to 35%), which need three to four coats, or more. Solids are what give polyurethane its hard protective layer, meaning you’ll get more protection and coverage with oil-based versus water.
Depending on the brand, one gallon of water-based polyurethane will cost between $40 and $60 a gallon and will give you around 600 square feet of coverage. Oil-based polys have the advantage of being cheaper, running around $25 a gallon, but will only give you 400 square feet of coverage due to its greater thickness. However, you do get to save money in that you won’t need to apply as many coats for coverage.
Water-based polys are best when working with light-colored woods to highlight the natural grain line without changing the wood’s color. The honey amber color of oil-based polyurethanes can cause light floors to take on a yellow hue that intensifies over time, distorting the natural color of the wood.
Woods like Maple, Ash, Pine, and Fir look best with a water-based finish. The same goes when working with white or gray stain or whitewashed woods. Water-based is also best when there’s a need for fast-drying applications or when there’s a sensitivity to strong odors.
Oil polys are better in areas that experience high traffic due to the material’s higher resistance to solvents, moisture, and heat. It’s also a suitable choice for when you want to change the color of the wood, or you want to give the wood a rich, warm honey glow, like with rich wood species such as Brazilian Cherry or Walnut. Other areas where oil-based polyurethane works best include railings, countertops, or cabinets.
Is Water Based or Oil Based Polyurethane Better?
Given the differences between oil and water-based polyurethanes, you’re probably wondering when it’s better to use each product. First, check out some common projects that use polyurethane and when to use oil-based or water-based.
Hardwood floors can benefit from either type of poly, but some situations can affect which kind would work better. Consider these seven factors:
- Location – some places have government regulations (like California) that prohibit the use of oil-based finishes; oil-based is more common in rural areas while water-based is more common in urban markets (except the Northeast)
- Budget – oil-based is less expensive than water-based, but doesn’t cover as much
- Drying time availability – do you have the time to keep the space vacant for the length of time necessary to do all the coats (one – water – to three days – oil)
- Appearance preference – clear (water) or honey-hued (oil)
- Odor sensitivity – water-based has little to no smell, while oil-based is very strong smelling
- Thin and hard (water) or soft but thick (oil) coating
When working with furniture, one consideration is the wood and how you want the piece to look when finished. You’ll also want to consider how much traffic the wood piece sees and the intensity of use. For heavy traffic pieces, oil-based poly would offer more protection than water-based.
Oil-based polyurethanes are an excellent choice for tables because this finish offers resistance to scratches, stains, and water damage. It also gives the surface increased durability and color radiance. Water-based polys have benefits like faster drying and curing, strong durability, and easier application and cleaning. While also providing a clear coat that keeps and enhances the wood’s color without altering the tone.
Polyurethanes used outdoors should be top quality and specially formulated for outdoor or exterior use. In addition, you’ll need a product with UV absorbers and that provides enough solid content. If no regulations prevent the use of oil-based polys, you may find better benefits with this type. Otherwise, you’ll have to use the more eco-friendly water-based.
Polyurethane is an excellent finish to use on butcher blocks. It protects the wood from damages due to rough use and moisture and also makes the wood look and stay outstanding. Oil-based poly (and water-based to some extent) can give your wood counters more of a plastic look, hiding the natural beauty of the wood. Many kitchen experts recommend a natural oil finish instead.
The heavy and frequent use of kitchen cabinets, plus the reduced likelihood of exposure to water and other liquids, means that kitchen cabinets can benefit from coverage with oil-based poly. If using a water-based poly, you’ll want to add additional layers to account for the thinness of the liquid plastic to give it the same toughness as an oil-based product.
Can You Use Water-Based Polyurethane Over Oil Stain?
Although oil and water typically don’t mix, you can add a water-based polyurethane over an oil stain without messing up your wood or its look. Technically, the poly doesn’t mix with the stain, it creates a separate layer over the top.
You will need to give the stain time to fully dry before coating the wood with oil or water-based polyurethane. You may experience slight color changes in stained wood when using water, despite applying and drying into a translucent coating.
Can You Put Oil-Based Polyurethane Over Water-Based Stain?
You can also apply oil-based polyurethanes over a water-based stain, provided you follow the proper application rules. The main thing to remember is that when working with an oil-based poly and a water-based stain, you’ll need to wait a minimum of 24 hours for the water-based stain to dry completely before applying the oil varnish.
Using Polyurethane Over Paint
Adding one to two coats of polyurethane to painted walls is a great way to extend the color’s life and vibrancy. It also doesn’t matter what type of paint you’re covering, for poly can work on any of it! However, the painted walls must be properly cleaned and prepped before applying each new layer of poly.
While oil will take longer to dry, possibly becoming an inconvenience while you’re limiting the space’s use, it gives you a smoother finish. You’ll need to allow freshly painted walls 24 to 72 hours to dry before starting the poly application.
Best Oil-Based Polyurethane
The clear color means that the protective coating will enhance the wood’s natural color with a shiny sheen instead of turning it yellow. Some people, though, may find that the translucence makes the wood feel a bit cold. Use this finish for stairs, doors, woodwork, floors, furniture, and cabinets.
Best Water-Based Polyurethane
You can use soap and water to clean up any messes, and there are little to no VOCs, making it great for beginners, despite the clear color. However, you will need to use multiple layers to get full protection against scratches and stains on trim, furniture, cabinets, and windows.
Polyurethane – a type of liquid plastic – comes in two chemical makeups: water-based or oil-based. While you can generally use both types to coat wood, there may be instances where one type would be preferable over the other.
Remember that oil-based polys have a higher chance of changing your wood’s color to more of a golden tint while water-based stays clear. Water-based is thinner and requires more coats, while oil-based only needs two or three. Plus, you’ll need to handle the smelly harmful fumes that oil-based products produce as they cure. Hopefully, you have a better understanding of which polyurethane to choose, oil-based vs water-based.