Do paints expire? Many people will quickly proclaim – no – which is generally true as paints tend to last long. But is this true for spray paint?
Spray paints don’t last as long as traditional liquid paint or powder coats. However, most spray paints expire within ten years. Read on to find out more.
You first need to understand the chemical composition of spray paints to understand why spray paints eventually expire and how long a spray paint can last without opening.
Spray paints used in wood finishing comprise several pigments, solvents, binders, and propellants compressed inside a can.
- Pigments: Pigments add color and opacity and typically include white pigments, color pigments, inert pigments, and functional pigments.
- Solvents: Meanwhile, solvents are the liquids that carry the rest of the paint ingredients. Water is the most common solvent. However, organic solvents are also common.
- Binders: Paint binders enable the hardening process and facilitate the production of the hard film left behind once the paint dries. Thus, the binder directly impacts paint adhesion, washability, fade resistance, and gloss retention. Most manufacturers use acrylic polymers, alkyd polymers, and epoxy polymers as binders.
- Propellants: Finally, spray paints contain propellants to force the paint out of the can. Paint propellants are typically gases that expand rapidly when the valve is opened. Initially, chlorofluorocarbon (CFC) gases were the go-to spray paint propellants. Today, most manufacturers use hydrofluormethane and tetrafluoromethane.
Unfortunately, these components are not 100% stable. So, they constantly react within themselves and with other chemicals.
For instance, HFCs are short-lived chemicals. The standard HFC has a shelf life of 15 years, even in the most stable environment. However, the components disintegrate, and the product falls apart after this period. Pigments have the same lifespan.
Worse still, storage greatly impacts the lifespan of unopened spray. For instance, different chemicals are more active or inactive in different temperatures. For example, a common issue is color change due to temperature, known as thermochromism. Exposure to high temperatures can completely degrade the color pigments in spray paint.
Any changes to any paint component affect its effectiveness and directly impact its lifespan.
Generally, unopened spray paints last between two and ten years in optimal condition, depending on the paint type.
For instance, brands such as Krylon and Ironlak openly warn their customers that their spray paints have a 2-5 year shelf life. However, some unopened spray paints from brands such as Montana can last 15 years with proper maintenance. Therefore, it’s best to check the manufacturer’s sell-by date.
Opening paint cans significantly reduces the lifespan of spray paint. Indeed, you may not be able to use the paint as usual within a year of opening the can.
However, the general rule is that opening the lid halves the lifespan of the can. Therefore, if the spray paint originally had a lifespan of four years, opening the can halve the remaining lifespan to two years. It all depends on the type of paint, duration of exposure, and type of exposure (moisture, UV, etc.). The following are a few guidelines to consider;
Many spray paint components easily react with water/moisture. For instance, the paint solvent is diluted upon contact with water. HFCs also readily react with moisture, producing acids.
Therefore, non-waterproof spray paints, typically latex acrylic paints, last a very short time after opening the can. The paints can last five or more years if you keep them away from moisture and rainfall. However, they quickly lose their integrity upon moisture exposure, degrading completely in a few months.
On the other hand, waterproof (oil-based) spray paints aren’t significantly affected by moisture exposure. Therefore, opening the can does not significantly impact the paint’s lifespan. As a result, a new waterproof spray paint often remains in good condition for 10+ years after moisture exposure.
Besides water/moisture, direct sunshine exposure presents the biggest danger to spray paint integrity. The sun affects sprays in two main ways; temperature changes and UV radiation.
- Temperature changes
As we mentioned earlier, the storage temperature greatly impacts the paints’ lifespan. It affects nearly every component of spray paints and can trigger unwanted reactions between various components.
For instance, using spray paint in sunny weather may significantly raise the temperature of the paint. The same applies if you store it in a hot place. If you’re wondering, direct sunshine exposure increases the temperature impact due to radiation. Higher temperatures can cause pigment fading and alter the chemical composition of propellants. Furthermore, high temperatures rob paint of moisture, leaving it dry and lifeless.
- UV radiation
Opening the spray paint can also expose the paint to UV radiation. Ultraviolet light easily causes oxidation, a process that accelerates color loss. It adds oxidation agents, such as Ozone (O3) or single oxygen atoms, to compounds by breaking down other compounds through photodecomposition.
Additionally, taking oxygen atoms from some compounds and adding them to other compounds alters the chemical composition of the various paint components, potentially triggering unwanted reactions that can degrade the paint.
Generally, the lifespan of spray paint after opening the paint can is half the original lifespan. So, for instance, if the spray paint has four years left of its shelf life, opening the can cuts the shelf life to two years.
However, it also depends on the type of paint. For instance, Rustoleum spray paint lasts 4-7 years before opening but fades immediately upon UV exposure. Meanwhile, acrylic spray paints that naturally last three years can last about two years after opening the can.
Spray paints don’t last forever. Although they can last a long time, sometimes 15+ years, they eventually expire. More importantly, opening the spray reduces the paint’s lifespan, sometimes rendering new paint useless within a few months.
Therefore, it’s important to check the sell-by date when shopping for spray paint, open the can only when you’re ready to paint, and properly store unopened and opened spray paint cans.