Does paint go bad? A homeowner’s guide to longevity and disposal

Reusing leftover paint from a previous job for a new project is one way to save money on painting. But this leaves you wondering, “Does paint go bad?" 

Well, paint does have a shelf life, and if it’s not stored correctly, it can spoil over time. When paint goes bad, it can develop a foul odor, separate into layers, or dry up into a thick, unusable consistency.

Keep reading to learn more about how long each paint type lasts and how to extend its lifespan.

Does paint expire?

Yes, paint has a shelf life. The length of time it lasts depends on the paint type, ingredients used, and how it's stored. For instance, acrylic paint lasts about a decade when unopened and stored correctly, while oil-based paints can last much longer.

Paint must be stored in a cool, dry place, tightly sealed after use away from direct sunlight to extend its lifespan. Its shelf life expires due to the separation of ingredients and the evaporation of solvents used to keep it liquid. 

Average lifespan of common paint types

How long is paint good for? The answer varies depending on the paint type and storage conditions. Here’s an overview of the average lifespan of common paint types:

• Oil-based paint: Oil-based paint generally lasts up to 15 years when unopened. However, once opened, its shelf life decreases significantly due to the evaporation of solvents and oxidation.
• Acrylic paint: Lasts around 10 years when unopened. After opening, the lifespan reduces to 1 to 2 years if stored properly.
• Latex (water-based) paint: If unopened, it lasts 10 years. However, if not stored correctly, the water in latex paint evaporates over time, causing the paint to thicken and making it impossible to use.
• Chalk paint: Lasts 1 to 3 years once opened. Due to its thicker consistency, chalk paint can develop a lumpy texture if it’s not stored correctly. It’s generally more prone to deteriorating over time than other paints. As such, storing it in a cool, dry place is critical.
• Milk paint (mixed): When unopened, milk paint in its powdered form lasts about 1 to 2 years. However, once mixed with water, it only lasts a day or two due to the presence of milk proteins, which can spoil quickly.
• Paint primer: Depending on the manufacturer, paint primer can last between 2 and 10 years if left unopened. Like other paints, primer can thicken over time, especially if exposed to air.

How to tell if paint has gone bad

Concerned about your leftover paint and asking, "Does house paint go bad?" Look for changes in texture and consistency, foul odor, separation of ingredients, or mold growth inside the can.

Key signs of bad paint

Here are some important indicators of paint that’s past its shelf life you should look out for.

• Foul odor: A sour, rancid, or foul smell indicates that paint has gone bad. Latex or water-based paints, in particular, can grow mold or bacteria if exposed to moisture or air for too long, which leads to the strong, unpleasant odor. Even oil-based paints can develop a foul smell due to the oxidation process or the degradation of the solvents.
• Lumpy or thick texture: If the paint has thickened or developed lumps, it may be too old to use. When you stir it, the paint should be smooth and uniform.
• Separation issues: If the paint shows clear liquid on top or pigments that have settled at the bottom of the can, the paint has gone bad. Most paints will separate over time but are re-blended by stirring them well. However, if the liquid on top is thick or the pigment won't mix back in even after vigorous stirring, the paint has expired.
• Rust or mold inside the can: Rust can contaminate the paint, causing it to develop a gritty texture or become uneven when applied. Mold growth happens when moisture gets trapped inside the can due to improper sealing or exposure to high humidity. If you see black, green, or fuzzy growth on the paint’s surface or lid, it's a sign that bacteria or fungi have compromised the paint.

Does paint go bad in a can?

Paint can go bad in a can if the storage conditions aren’t right. Should the paint get too hot, the solvents will evaporate faster, causing the paint to thicken and become difficult to use. If the paint freezes, it can cause it to curdle or separate.

Likewise, if the paint is not tightly sealed, air can enter and accelerate its degradation. Over time, it causes chemical changes, such as oxidation in oil-based paints or polymerization in latex paints, making the paint more viscous and harder to work with.

Moisture exposure is also a significant risk. If the can is stored in a humid environment and not sealed properly, water can seep into the paint and cause mold or bacteria growth, leading to a foul odor, changes in the paint’s texture, or a slimy surface.

Do different paint types go bad?

Each paint type has its expiration timeline and deteriorates differently due to its ingredients and chemical processes. 

• Latex paint deteriorates mainly from water evaporation, causing it to thicken and develop a lumpy texture. It is also prone to mold and bacterial growth if exposed to humidity. 
• Oil-based paints degrade mainly through oxidation, which hardens and thickens the paint as it absorbs oxygen from the air. 
• Chalk paint suffers from water evaporation, which causes it to thicken and become clumpy if exposed to air. 
• Acrylic paint has similar issues, with water solvent evaporation leading to thickening and forming a crust. 
• Milk paint contains casein protein, which can break down or curl if exposed to moisture or extreme temperatures. It’s also more susceptible to bacterial growth or mold because the protein serves as a food source if exposed to air for long periods.
• Primer faces an evaporation and separation issue, causing it to become lumpy or lose adhesion properties. Oil-based primers experience oxidation and solvent evaporation, thickening and making them hard to apply.

Does acrylic paint go bad?

Yes, acrylic paint can dry out and become thick or clumpy over time due to water evaporation. To revive dried-out acrylic paint, add water, acrylic mediums (like an acrylic flow improver or glazing medium), or a paint extender to thin the paint and restore its consistency. For extremely dried paint, add a small amount of isopropyl alcohol to soften it.

Does oil paint go bad?

Oil paint lasts longer than water-based paints but can also go bad. Over time, oil paint experiences thickening as solvents evaporate. It also separates, with pigments sinking to the bottom and oil rising to the top. However, if stored in a tightly sealed container in a cool, dry place, oil paint can maintain its usability for many years.

Does paint primer go bad?

If left unopened and stored correctly, paint primer can last two to ten years, depending on the manufacturer. However, once opened, its shelf life is significantly shorter. If your paint primer is going bad, you will notice a thickened texture, lumps, separation of liquid and solids, or foul odor.

How to make paint last longer

These best practices can stop your paint from going bad and make it last longer:

• Store paint in a temperature-controlled, dry space, ideally between 50°F (10°C) and 80°F (27°C), away from direct sunlight, heat, and humidity to prevent it from freezing, thickening, or separating.
• Cover the surface of the opened paint with plastic wrap before sealing the lid to minimize air contact.
• Store paint cans upside down to create a seal that prevents air from entering.
• Add additives like paint extenders, flow improvers, mildew inhibitors, and drying retarders to enhance paint performance and improve consistency.
• Label and date opened cans to track how long they've been in storage.

Using additives for old paint

When dealing with old paint, additives can help restore its consistency and extend its usability. To thin latex or water-based paint, add a small amount of water. Carefully pour in just a little liquid and stir thoroughly to avoid over-thinning.

You can also use an appropriate paint thinner or mineral spirits to thin oil-based paints. If the paint has separated, stir thoroughly with a sturdy stick or an electric drill to mix the components. 

How to dispose of expired paint

Due to their different chemical compositions, the disposal method for expired paint varies between latex and oil-based paint. Latex paint, being water-based, can be safely discarded with regular trash once it’s thoroughly dried out.

On the other hand, oil-based paint contains hazardous chemicals and solvents, so it requires special disposal through a hazardous waste facility or a designated paint recycling program.

Does paint go out of date?

Paint goes bad over time, especially if it’s not stored correctly. Proper storage can help extend paint’s lifespan. Simple practices like keeping the cans tightly sealed and in a cool, dry place away from direct sunlight are essential.

Before using old paint, always check for signs of spoilage. If it’s lumpy, smells off, or doesn't mix properly, dispose of it safely to avoid damaging the environment.