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Materials

What are the Pros and Cons of Urethane Coating?

By CW Deziel
Updated May 17, 2024
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Even though a urethane coating provides superior protection on wood and metal, it is not always the best option for a finish coat. Urethane, or more appropriately, polyurethane, is an artificial polymer and, although its impact resistance surpasses that of lacquer and shellac, it does not penetrate wood in the same way and remains on the surface. A urethane coating levels out well on metal and will adhere to any previous finish, but its plastic appearance can be displeasing. Although it typically is affordable, urethane is not the least expensive finish material available.

Whereas lacquer and shellac, which are natural polymers, harden by evaporation of the solvent in which they are carried, a urethane coating has to cure. As the solvent evaporates, the polymers form by reacting with chemicals in the paint or with moisture in the air. The final finish is more resilient and durable than one created by natural polymers, but the waiting period between successive coats is longer. Depending on the curing process, this period can be anywhere from two hours to two days, and until curing is complete, the surface can't be sanded and has to be protected from dust.

The polyurethane polymer is engineered to provide higher chemical resistance than natural polymers. For this reason, a urethane coating is much less vulnerable to spotting or discoloration than other coatings, which makes it a better choice than lacquer for countertops and bars, where spills are frequent. It has a higher impact resistance, so it is also less likely to chip under the abuses that these surfaces suffer. Enhanced chemical and impact resistance make urethane an effective automotive finish, but applying it correctly requires care because it doesn't flow out of the spray gun as easily as lacquer or enamel. Furthermore, the toxicity of the ingredients in automotive urethane requires the use of expensive protective clothing, eyewear and a respirator connected to an air pump.

Paintable urethane products for use on wood are available in oil-based and water-based varieties. In contrast to urethane products for automotive use, water-borne polyurethane wood finish is non-toxic, and the fumes that it produces are safe to breathe. The excellent impact resistance and longevity of either oil- or water-based polyurethane finishes make them suitable for floors, although the plastic-like appearance of a urethane coating might detract from the appearance of certain varieties of wood, especially dense exotic hardwoods such as teak and mahogany. These woods might look better if left unfinished or simply coated with oil.

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Discussion Comments

By Mykol — On Dec 07, 2011

I don't mind working with polyurethane, but think it does take some patience. I have used this for several projects, and have consistently been happy with the results.

There are a few things that make working with this a little easier. I have found best results when using a high quality bristle brush. I know some people like to use the disposable foam brushes, but I think the natural bristles work best.

Another thing that helps is to make sure the place you are working is free of dust. There is nothing more annoying than particles of dust and dirt that make for a rough finish.

If I am using wood, I always make sure I start out with a smooth surface - that is half the battle right there. Two coats of polyurethane are usually enough for the projects I have completed.

I also found out the hard way to wait 24 hours before applying the second coat. Once I got in a hurry thinking it was dry enough for the second coat. It wasn't completely dry, and the finish ended up not being very smooth.

That is where the patience comes in to play!

By honeybees — On Dec 06, 2011

If you are new to wood working and staining, I think using polyurethane is an easy way to get started.

I had some old pieces of wood laying around the garage, and thought they would make great shelves to store some of the kids toys on. I didn't have much money to work with, but wanted something to get the toys off the floor.

After sanding the wood, I painted them with bright, primary colors. I finished with a couple coats of polyurethane. I like the glossy finish it gives the shelves.

This is something that didn't cost me much money, and I see no reason they won't last for as long as I need them. When my kids don't need them any more, I am not out much money.

I kept the can of urethane that was left over thinking I will soon find another project I can use it on.

By Izzy78 — On Dec 06, 2011

@kentuckycat - I have used urethane on plain metal before without any problems. If you think the swing set is already starting to rust, though, it might not be a bad idea to get some of the rust preventing paint and give it a coat of that before you put on the urethane. I'm not sure how the swing is set up, but if you ever get water inside the pipes, that might slow down the process.

As far as applying it goes, I know what you mean by it being difficult to paint round things without causing streaks. In my experience, the best thing to use when you are putting on urethane is one of the sponge brushes. If you use something like a 1 inch brush, you shouldn't have any problems. The urethane should go on very smooth, and running should be minimal. Good luck.

By kentuckycat — On Dec 05, 2011

@jmc88 - I am not sure epoxy would really be a good move for an interior hardwood floor. At least in the instances when I have seen it used, it has been more for waterproofing types of jobs. I have used it on my deck outside, and I have known a lot of people who have used epoxy floor coating in their garages.

I think the standard for hardwood floors is usually urethane, because of the durability mentioned in the article.

I am curious if anyone here has ever tried using a urethane coating on metal. We have a swing set that is starting to get a few years old, and I am afraid it might be getting to the point where it is starting to rust in certain places. I would really like to put some sort of coating on it and try to stop the process.

I never knew how polyurethane worked before, but it sounds like it needs something like paint to cure with. Is that the case, or can you apply it directly to the metal and still have it work the way it is supposed to. As far as applying it, what would be the best method? I am afraid using a brush might leave behind marks, since the stuff I will be painting is round. I could get a sprayer, but the article makes it sound like that might be difficult, too.

By jmc88 — On Dec 05, 2011

Has anyone here ever used any sort of epoxy coating for their hardwood floors? I have been wanting to refinish the hardwood floors in my dining room for quite some time. I have been looking at all of the various options, and one of my friends suggested to me that I look into epoxy.

What exactly is it, and how is if different from a urethane coating or even something like lacquer or shellac? I guess the most important things that I would want to consider are look and durability. I am not really concerned with cost that much, since I figure it is better to spend more upfront for a long lasting finish than have to go back sooner and spend more money.

By JimmyT — On Dec 05, 2011

I agree with the article. The kind of finishing treatment you are going to apply to a piece really just depends on what kind of look you are going for combined with your budget.

I think for most things, a polyurethane coating is just fine. I have used it on a lot of things, and I have never felt like it really gave a plastic looking finish.

On the other hand, though, if I am ever refinishing any higher end pieces of furniture, I usually choose to go with shellac or lacquer. I didn't know they worked differently until now, but I guess it is something about the fact that lacquer and shellac sort of soak into the wood that makes the piece look more natural overall. They can make a piece of oak or walnut almost look like it is naturally shiny.

By ElizaBennett — On Dec 04, 2011

@SailorJerry - I covet urethane floor coating for my house! We have very old floors that the finish has long since worn off of. And we have small kids and a cat! I hate to see the floors get stains from baby drool, the occasional cat vomit, an apple juice spill, etc. Because they are really beautiful oak. Refinished and properly treated, they would really be something.

But it's a rental (a duplex, even, not a high end rental) and who wants to spend four or five figures redoing the floors in rental property? Ah, well, someday I will have proper floors.

By SailorJerry — On Dec 03, 2011

The difference between a floor with a worn-out finish and one with a new polyurethane coating is really remarkable. I grew up in a house that had beautiful hardwood floors (they had been covered with carpet during the 1970s and thus protected), but the finish was wearing out. As we kids went around being kids, we naturally spilled things, etc. and the floors picked up stains.

As my parents were getting ready to downsize, my mother knew the refinishing the floors would make the house much more appealing on the market. Having it professionally done would have been prohibitively expensive, so she rented a drum sander and went for it! The first room was just OK, but the next was perfect (and she went back and redid the first). She finished with polyurethane.

The floors looked beautiful, and they were so durable all of a sudden! Even a spill that wasn't wiped up right away wouldn't leave a stain.

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