Does Polyurethane go Bad? (Unopened vs Opened)

Polyurethane can go bad if stored improperly or past its expiration date. When polyurethane goes bad, it can become thick, difficult to apply, and may not adhere properly. To avoid this, store polyurethane in a cool, dry place and use it before its expiration date.

Polyurethane finish has a shelf life like any other wood finish and can deteriorate over time.

This article will discuss whether polyurethane can go bad and the factors contributing to its degradation.

I will also provide tips on properly storing and using polyurethane to ensure its effectiveness and longevity.

Polyurethane and Its Shelf Life – When Does it Go Bad?

SituationShelf Life
Sealed Polyurethane CanUp to 3 years
Opened Polyurethane CanAbout 12 months
Mixed with AdditivesUse within 6-12 months of mixing, depending on the product
Shelf life of polyurethane wood finish

Polyurethane is a commonly used finish on wood surfaces like hardwood floors. It has water- and oil-based options available.

These types of polyurethane have an estimated lifespan of 3 years. They even last longer when stored properly.

A good quality polyurethane will remain usable for up to 10 years if stored unopened and in recommended conditions.

But when opened, they can go bad in one year, and deterioration can occur faster when stored under extreme temperatures.

Another factor that can affect the shelf life of polyurethane is exposure to heat and light.

Technical data of polyurethane from Rust-Oleum
Technical data of polyurethane from Rust-Oleum

Polyurethane should be stored in a cool, dry place away from direct sunlight or heat.

Exposure to heat and light can cause polyurethane to break down and lose its effectiveness.

The shelf life of polyurethane can also vary depending on the type and formulation of the product.

Some types of polyurethane may have a longer shelf life than others, and some formulations may be more susceptible to degradation than others.

Polyurethane should be used before expiration. The expiration date is typically printed on the product label or packaging.

Expiry date printed on a polyurethane can
Expiry date printed on a polyurethane can

Ways to Check If Polyurethane Has Gone Bad

There are a few signs to look out for to determine if your polyurethane is bad or expired:

  • Check the appearance of the polyurethane. If it has thickened or has become clumpy, it may be expired.
  • If the polyurethane has a strong, pungent smell or a foul odor, it may be expired.
  • If the polyurethane feels gritty or has hardened and is difficult to stir or apply, it may be expired.
  • If the polyurethane takes unusually long to dry or remains tacky, it may expire.

If you notice any of these signs, it’s best to dispose of the polyurethane and purchase a new one to ensure the quality of your project.

Thinning Polyurethane
Pouring polyurethane on a container

Things That Happen to Stored Polyurethane Over Time

Stored polyurethane can degrade over time due to several factors, such as exposure to air, moisture, temperature, and light.

Here are some ways stored polyurethane can change over time:

  1. Thickening: The polyurethane can thicken, making it more difficult to apply.
  2. Separation: The polyurethane may separate into different layers, with the heavier solids sinking to the bottom and the thinner liquids rising to the top.
  3. Hardening: Polyurethane can harden and become difficult to stir or apply.
  4. Discoloration: The polyurethane can become discolored or develop a yellowish tint.
  5. Reduced performance: The performance of the polyurethane can be affected, with a decrease in its ability to provide protection and enhance the appearance of the surface it’s applied to.
  6. Odor: Polyurethane may develop an unpleasant odor or off-gassing.

It’s important to store polyurethane properly to prevent these changes from occurring.

Try to use the stored polyurethane within the recommended timeframe to avoid any potential degradation.

Tips to Extend Polyurethane’s Lifetime

Once opened, polyurethane tends to crust and cure, so it’s important to use it within six to 12 months before it becomes too hard to use.

To maximize its shelf life, you must take certain precautions in storing and handling it.

Polyurethane stored in a dry place
Polyurethane stored in a dry place

When storing, ensure it is in a sealed container to prevent air and moisture from entering.

Exposure to air and moisture can cause the polyurethane to cure or dry out, making it unusable.

Additionally, store the container in a cool, dry place away from direct sunlight and heat sources.

Extreme temperatures can accelerate the curing process, making it unusable.

Polyurethane will also settle over time, causing the heavier components to sink to the bottom of the container.

Before using it, thoroughly mix it to ensure the ingredients are evenly distributed.

Final Thoughts – Will Wood Finishes Go Bad?

It’s worth noting that all wood finishes can go bad over time as they are made of chemicals that can break down and lose effectiveness over time.

Factors such as temperature, humidity, exposure to air, and exposure to sunlight can also influence this degradation.

Polyurethane exposed to sunlight
Polyurethane exposed to sunlight

While unopened cans of polyurethane can last up to three years, opened cans can only last about a year or more, depending on storage conditions.

If you mix polyurethane with additives, use it within 6-10 months, depending on the product.

To extend the lifespan of wood finishes, store them properly and follow the manufacturer’s instructions for use.

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Frequently Asked Questions

How long does polyurethane last once open?

Once opened, polyurethane can last up to 12 months if stored properly in a sealed container and away from extreme temperatures. However, it may deteriorate and become too hard or thick to use within six months in some cases.

Does polyurethane go bad if it freezes?

Yes, polyurethane can go bad if it freezes. It may become thick, gummy, or discolored when exposed to freezing temperatures, making it unsuitable for use. It’s important to store polyurethane at room temperature and avoid subjecting it to extreme temperatures.

How do you keep polyurethane from going bad?

Store polyurethane in an airtight container away from sunlight, heat, and extreme temperatures to keep polyurethane from going bad. Use plastic wrap over the can before sealing the lid. Always clean the can’s rim before recapping and store it in a cool, dry place.