How long does leftover interior paint last in storage? (I live in Bothell, WA) - RitePainting

How long does leftover interior paint last in storage? (I live in Bothell, WA)

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It seems like everything we buy in a can tells us to “store in a cool, dry place”. Well, the same goes for any kind of paint. Ideally, unused paint – or yet-to-be-opened cans of paint for that matter – should always be kept in a cool, dry place. What’s more, it should never freeze, as this can alter the chemical makeup of water-based paints, in particular.

Paint begins its journey the moment you open the can

Paint was simpler decades ago. Today, the lead additive is gone – by federal law, at least when it comes to domestic use of paint – but paint is a far more sophisticated substance that it was then. Paint manufacturers pour (no pun intended) millions of dollars of cash into research and development every year in the hopes of finding new, more competitive products to bring to the market. They have teams of chemical engineers, designers and product managers working full time on such activities. The result? Paint products that are finely tuned to specific needs and made to solve specific problems. Ultraviolet light protection, faster drying, better adherence to surfaces, and fade resistance are just a few characteristics that come to mind. Paint is designed to last long in the can, and to start working hard the moment you open that can.

Once paint is exposed to air, it is changing. There are two basic processes that occur from that point, the first of which is, it begins to dry. No secret there, but the other important process is what’s called ‘curing’. Curing is what the paint does over the next several weeks while it sits on your kitchen wall. When the paint first dries, which does not usually take long, it’s easy to think the job is done, but the curing is essential. In that second stage, the paint is actually becoming more robust, and fixing its bonds with the surface it has been applied to, as well as finishing up the chemical processes that began when the can was opened. In oil based paints it can take a month or more, and it is why it’s best to leave the paint undisturbed for that time. It’s also why, when you get a part or all of your car resprayed, they recommend you do not wash it for weeks after the work is completed. The paint is curing, even though it is bone dry to the touch.

Keeping unused paint is not always wise

Not all paints are flammable, but many are. Oil-based paints especially. But it’s not just the paint itself that can cause a problem. If a one-gallon can of paint only has a few fluid ounces of paint in the bottom of it, it has plenty of air above it, and room for vapors to leave the paint and build up in that free space. Now consider the situation where you have several cans of paint stored in your garage. On a hot summer’s day, your home might feel comfortable, but your garage can climb over a dozen degrees hotter than the ambient, outside temperature. Your garage acts like a greenhouse, heating everything in it. It’s fine for the cars – they are built to take the heat – but when your leftover paints get hot, they can explode. With the right – or should I saw unfortunate – set of circumstances, vapors can ignite, starting a fire in your garage in the middle of the afternoon. You may not have a fire or smoke detection system in your garage, in which case the fire can truly get hold before emergency services are called.

My advice is, once a can is opened, you should not keep it after the painting project is done. Even if it does not start a fire, vapors can escape from old cans of paint, and in small enough volumes for you not to notice. Still, they are seeping into your living space – from the garage, crawl space, attic or spare room. That can’t be healthy.

If you really want to keep some paint that matches your paint project exactly, for about five dollars you can buy a ‘tester’ sample. It’s essentially a miniature version of the full size can of paint, and it can be stored far more safely. Be sure never to open it, though, until you need to use it.

Leaving behind a few paint samples for a future owner of your home, by the way, is also an added benefit to someone buying your home, and may therefore help you close the deal when that time comes.

Garage, basement, crawl space, spare room or attic?

If you truly must keep the paint, consider pouring it into perfectly sealable jars. The less air is in the jar, the better, as less air will keep the paint fresh for longer.

Attics tend to get hot in the summer and cold in the winter. On midsummer days, an attic, like a garage, can become far hotter than the air in the street outside, and certainly hotter than the interior of your home, assuming your insulation has been installed well.

If you ever want to see who has the best insulation in their attic, when it snows, the roof in the neighborhood with the poorest insulation will see their roof snow melt first. That tells you the heat from inside the house is reaching the attic, and from the attic to the roof. If the top floors of your home are well insulated from your attic – something that helps keep your heating bills low – it means that the attic may well drop in temperature below freezing. If it goes low enough, it can cause the paint container to fail, and if it gets hot enough, it can cause the container to explode. Paint should not be stored in an attic.

Inside your living space is also not a good place to store unused paint, especially if the containers have been opened and closed again. It’s almost impossible to reproduce the perfect seal of lid on can put there by there paint manufacturer. It’s unlikely that you will be able to close it perfectly, and now there’s the extra chance that paint vapors will escape and your family will be breathing that.

The best and safest recommendation is to simply get rid of all the unused paint when the project is completed. Document the exact paint colors and types you used, so you’ll always be able to go to the store and get more when you need it.

Enjoy the summer, and we’ll talk again next week!

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