Homeowners often encounter old paint cans stored in basements, garages, or crawl spaces. These containers can be unopened cans left behind by previous owners or partially used from past projects. It is natural for homeowners to consider using such leftover paints for new projects or quick touch-ups.
However, the biggest concern here is the usability of these paints, which depend on their shelf life. The shelf life depends on various factors, including the type of paint (oil-based or latex) and storage conditions. Understanding these factors helps homeowners determine whether old paint can be reused.
How Long Does a Can of Paint Last?
Usually, an unopened can has a longer shelf life than a partially used can. However, there are a few factors that help understand the expiry date of a can of paint. In addition to whether it was opened, the type of paint also plays a significant role in determining the shelf life, as discussed below.
Water-Based Paint
Water-based latex and acrylic paints have a shelf life of 10 years when stored unopened under ideal conditions. It should be tightly sealed and protected from extreme temperatures to help extend its shelf life.
Oil-Based Paint
This type of paint can last more than 15 years if left unopened. However, once it has been opened and used for any projects, the shelf life gets reduced to about 5-10 years.
Limewash Paint
Limewash paint offers a shelf life of 5 to 10 years, with unopened containers lasting much longer. This type of paint is usually made of lime, water, and pigment. This combination of ingredients makes it last longer without going bad.
Chalk Paint
Chalk paint has a relatively short shelf life of up to a year; however, a few manufacturers produce chalk paint that can last longer. Unlike latex paint, chalk paint does not form a film; instead, it develops a thicker consistency over time. Adding water can revive older chalk paint that has thickened.
Milk Paint
Mixed milk paint has an extremely short lifespan of only one or two days because of its milk protein content. Refrigerating this type of paint can possibly extend its shelf life to one week. And some milk paints contain additives that help them to prolong their shelf life. However, unmixed dry powdered milk paint can last indefinitely when stored in a dry, cool place.
Spray Paint
This type of paint usually lasts 2 to 3 years without going bad. However, it is best to check the expiration date on the can, as the propellants degrade over time.
How to Tell if the Paint Has Gone Bad?
Here are a few ways to determine if your can of paint has expired or gone bad.
The Paint Has a Pungent Smell
Fresh paint usually produces a strong but clean odour. When paint goes bad, the bacterial growth develops inside the can, resulting in an unpleasant smell. This odour is like rotten eggs, curdled milk, or swamp water.
When opening a can, if you smell a sour, pungent odor, it indicates the paint should not be used. If used, the house and walls are likely to smell rancid as well.
Change in the Texture
Usable paints can be stirred easily and smoothly. However, expired paint is clumpy, lumpy, or jelly-like. Latex paint often develops a thin film on the surface, but a thick skin on the latex paint is a sign of a serious problem.
Thoroughly stirring the paint may help restore it. Even adding a small amount of paint thinner to oil-based or water-based paints can help solve the problem. If these measures fail to bring the paint back to its natural consistency, it is best to dispose of it.
Development of Rust on the Paint Can
Rust on the exterior of a paint can does not mean the paint has expired. However, it is important to check if the rust has contaminated the paint inside the can. Rust-contaminated paint can stain any surface.
While opening a rusty can, make sure to prevent rust flakes from falling into the paint. This offers a slim chance that the paint will be usable without contamination. However, if the rust particles are visible in the paint, it is best to discard the can.
Growth of Mold or Mildew
This growth is often due to improper paint storage. If it is not tightly sealed, there is a high chance of mold or mildew entering the paint. It is best to avoid using paint contaminated with mold or mildew growth. It is crucial to dispose of paint properly at a hazardous waste facility, as exposure to expired paint can be dangerous.
Colour Has Changed or Separated
Discolouration confirms that the paint is no longer usable. White paints that have gone yellow or deep colours that have faded to lighter shades indicate expiration. Colour separation is often normal because the solid eventually settles to the bottom and the liquid rises to the top.
It is better to stir the paint to thoroughly mix the formula; if not, a professional at the paint shop can mix it. If the paint remains separated after all these efforts, it should be discarded and replaced with a fresh can.
Dangers of Using an Expired Paint
It can indeed be hazardous to use expired or old paint. Products made before 1978 may contain lead, a toxic substance. Expired oil-based paints often release harmful fumes that can be toxic and dangerous. Latex paint made before 1990 also contains mercury, which can pose a serious risk to family members. It is important to properly dispose of paint to avoid health hazards and environmental damage.
Conclusion
Paint does expire, but not all old paints are unusable. It is important to carefully store them under the right conditions and at the right temperature, which helps extend their shelf life. When paint has gone bad, it is important to dispose of it properly to avoid health and environmental hazards.
