Before you can decide whether water based polyurethane or oil based polyurethane is best for your project, you need to define what you want the end result to look like and how you want it to perform.

Let’s start with why you would use polyurethane in the first place vs. other types of wood finishes such as shellac, lacquer, varnish, etc.

Based on my 30+ years using and formulating wood finishes, it is best to use a urethane when your primary objective is maximum chemical resistance and film hardness, i.e., durability. It’s no accident wood floors, for example, are usually finished with urethanes.

With that in mind, here is a head-to-head comparison of how water based polyurethane and oil-based polyurethane stack up.

There can certainly be exceptions (some of which are noted below) but the below overview should make your decision easy 90% of the time…

 

Final Finish Look and Feel

A well-engineered, water based polyurethane will be equal in clarity to oil-based polyurethane. The main difference is usually color: water based polyurethanes are completely clear and (again, if well engineered) will not yellow over time. This is ideal if you want the natural color of your wood to remain constant. Some people prefer the warm, “amber” hue that oil-modified polyurethane imparts to wood, but keep in mind, this “yellowing” will continue and intensify over time.  In terms of “feel,” because it’s thicker, one coat of oil-based poly would probably feel softer than water based poly (but rarely is only one coat of water based poly used). Likewise, some people find oil based poly dents and peels easier, whereas water based poly might scratch easier. Keep in mind that there are variations to each urethane type, so read the product spec sheet carefully.

Winner: Tie (+1 to each)

 

Durability

Oil based polyurethane had the edge here for a while, but water based polyurethane (especially the self-crosslinking variety) has caught up – it’s now equal to solvent based products regarding scuff, mar, UV, water, and corrosion resistance. If you’re trying to make something virtually bombproof, oil based may be the way to go, but the hazardous additives and flammable solvents you’d need means you would almost be making a bomb.

Winner: Tie (+1 to each)

 

Safety

Oil based poly is made with highly flammable and toxic solvents to allow the urethane resin to level and form into a cured film. The clean-up process, too, requires exposure to high-odor hydrocarbon solvents now well documented to cause short- and long-term health problems. A well-engineered water based poly usually contains little or no ingredients considered “hazardous chemicals” as defined by OSHA. Likewise, a good water based poly will have significantly lower (up to 50% lower) volatile organic compounds or VOCs.

Winner: Water Based Polyurethane (+1)

Drying and Re-Coat Time

All things being equal (temperature, humidity, etc.) oil based polyurethane will take about two to three times longer to dry between coats compared to faster-drying water based polyurethane.

Winner: Water Based Polyurethane (+1)

 

Number of Coats Needed

The water in water based polyurethane tends to “react with the grain” more, so you often need to apply more coats to achieve a smooth, finish. A good rule of thumb: for every coat of oil based polyurethane, you may need to apply at least two coats of water based polyurethane.

Winner: Oil Based Polyurethane (+1)

 

Number of Coats Available

With a water based poly, you have unlimited coats available. Want to put on six layers? Go for it. Oil based polyurethane, on the other hand, is prone to “sheeting,” scratching or chipping after the first couple layers.

Winner: Water Based Polyurethane (+1)

 

Compatible Substrates and Adhesion

Water based polyurethane is extremely versatile; it will bond to nearly anything including wood, (non-ferrous) metal, fiberglass, stone, cement and carbon fiber. Oil based polyurethane adheres well to nearly everything, too…except itself. That means you must sand it between coats to create a mechanical bond to the next layer.

Winner: Water Based Polyurethane (+1)

 

Cost

The raw materials used to make water based polyurethane cost more than that of oil based polyurethane, so the final price you pay is typically higher, too.

Winner: Oil Based Polyurethane (+1)

 

Application & Equipment

You can find both types of polyurethane in brush- and spray-friendly versions, so “ease of application” is a tie. However, the low solvents in water based polyurethane gives it a longer “pot life” (the amount of time you can work with it before it becomes unusable) and it is easier on your equipment.

Winner: Water Based Polyurethane (+1)

 

If we add everything up, here’s the scoreboard:

Water Based Polyurethane (+7)

Oil Based Polyurethane (+4)

Depending on the importance or “weight” you place on the categories above, your scoreboard might come out looking differently.

For example, for me, safety to the wood finisher and the environment is worth at least +5 points, in which case water based polyurethane wins by an even larger margin.

What do you think? Do you have experience using (or questions about) water based poly vs. oil based poly?

Please share your thoughts or read what others are saying in the comments section below.

As always, stay safe and stay creative!