How to Tell If Polyurethane is Bad

Since nothing lasts forever, then it happens to polyurethane too. Even if you haven’t used it and it is properly stored, sooner or later, it will be expired. So how to tell if polyurethane is bad? How do you recognize it?

Does Polyurethane Go Bad?

The answer is definitely yes. Everything will go bad whatever it is and how expensive it is. How long polyurethane goes bad depends on some factors, one being the condition of the can.

If it is an opened can of polyurethane, it can last for around three years. An opened can of polyurethane lasts for just about one year.

Make your polyurethane last longer by storing it in an airtight container and keeping it away from fluctuating temperatures.

How Do You Know That Polyurethane is No Good?

Now that you know polyurethane can go bad, you might wonder how you recognize it. An opened can of polyurethane is usually exposed to the air.

Polyurethane is naturally dried when exposed to air, so it is normal when you find a hard layer of polyurethane at the top of the can. It doesn’t mean that the polyurethane is already expired.

There are some characteristics to tell if your polyurethane goes bad. Just take out the dry texture on the top of the can, and you will find the smooth texture at the bottom.

To identify whether or not your polyurethane is bad, check if it is separated into chunks. If it is, your polyurethane might have gone bad.

However, you can try to stir it and apply it to scrap wood. Bad polyurethane cant is applied evenly, just like a good one.

What Happens When Polyurethane Goes Bad?

When polyurethane goes bad, it has a sour smell. However, it is hard to recognize the sour smell because polyurethane originally had a strong smell.

Only those used to working with polyurethane can figure out the sour smell.

The easiest way to check if polyurethane is bad is by applying it to scrap wood. A good polyurethane will normally dry within 24 hours, while a bad one will still wet and sticky even after waiting for the same amount of time.

How Long Does Polyurethane Last Once Open?

Polyurethane lasts for about 4 to 6 years if it is unopened and last about 1 to 3 years if it is opened. So how long your polyurethane lasts depends on its condition.

An opened polyurethane lasts shorter because it is very prone to air. Once it is opened, it has a shorter lifespan, even if you close the lid tightly again.

This is because when the can is opened and closed again, there is still little air touching the liquid. The air causes the leftover polyurethane to harden over time while it is stored in the can.

As a result, the longer it is stored, the harder it will be. You can’t keep an opened polyurethane for more than three years.

Always notice some signs of bad polyurethane before using since it doesn’t have an expiration date on its can.

Why is My Polyurethane White in the Can?

What if your polyurethane turns after applying? Is it a sign of a bad one? No, it is not. It is a sign of something else. You might find some white spots after applying polyurethane, which could be because you haven’t stirred it before.

There might be a buildup of flattening agent that causes your paint to turn white, so you need to stir it first.

Another reason is that you put too much stain or just don’t let the stain completely dry before applying polyurethane.

Applying too thick polyurethane can also cause it to drips that turn into white spots. It is better to apply a thin coat in a large number than a thick coat in a small number.

Can I Store Polyurethane in a Plastic Container?

As mentioned above, polyurethane is so prone to air that it needs to be closed tight after being opened. Now, you need to learn where you can store it.

Using plastic containers for storing polyurethane is not a bad idea, but pay attention to the type of plastic you use. It cant be any type of plastic.

It should be the heavy one like Tupperware-type or a paint-type plastic container. This type of plastic withstands oil-based polyurethane, unlike the others.

However, storing leftover polyurethane in a resealable glass jar is still best. This kind of glass is usually very tight, which is all you need to keep the polyurethane safe from the air.

Make sure not to put the container upside down to prevent any leaks.

What Brand of Polyurethane is Best?

There are many polyurethane brands you can find in the store, and coming up with the best one should depend on what type of polyurethane you are looking for.

Whether water-based or solvent type of polyurethane, both are good and easy to use.

Polyurethane is younger than shellac, varnish, and lacquer, which have been there for centuries. Choosing the best means you need to consider what you need.

First, how is polyurethane going to be used? Is it indoor or outdoor? Is it for woodwork, floorings, or furniture? Do you want a plastic-like appearance from water-based products? Or a smoother finish from the solvent-based ones? You need to answer these questions before picking up the best polyurethane brand.

For interior woodwork, you can go with Varathane Ultimate Polyurethane or Minwax One-Coat Polyurethane; for exterior, you can have Minwax Helmsman Spar Urethane.

For wood floors, try Bona Mega Waterborne Wood Floor Finish or Minwax Polyshades containing various wood tones.

Is Polyurethane Toxic?

Although polyurethane is a great option to finish your woodwork, don’t forget that this is also a toxic chemical compound.

Petrochemical resin in polyurethane can lead to breathing issues like asthma. Uncured polyurethane can also cause vomiting, nausea, headaches, and throat irritation.

Leaving polyurethane to dry completely is very important to reduce its toxicity. It can be several hours or days, just take the time and don’t enter a room with uncured polyurethane.

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