Short Answer: The short answer is yes, paint does go bad.
Exposure to such things as the air, bacteria, and extreme temperatures can change the constitution of the paint, making it unusable. And this goes for both water-based and oil-based paint.
Sometimes it can be handy to keep a pot of paint even after you’ve already applied as many coats as you need.
Because interior walls can get dirty and moldy, and often, the best way to get them to look fresh again is to give the wall a new lick of paint.
However, if you’ve had your paint pot for a number of years, you’re right to wonder whether it will be of any use.
The truth is that while paint pots often have expiration dates (see also “Can You Use Exterior Paint Inside?“), if they are kept unopened and in cool but dry conditions, they can often be usable after periods of up to 15 years.
If they are opened, however, this shelf life will drop dramatically.
Coming Up
In this article, we will be discussing why paint goes bad over time, how long water and oil based paints will last if left unopened, and how best to keep them to prevent them going bad too quickly.
And then we’ll follow up with a solution, including how to tell if your paint has gone bad, and how to make old paint usable again.
And without further ado, let’s get straight to it.
Why Does Paint Go Bad Over Time?
Some older paints can be dangerous to use since they can emit harmful fumes that are toxic. For instance, paints made prior to 1978 may contain lead and even paints made in the 1990s contain mercury.
But potential toxicity aside, paint that has been opened without the lid being replaced tightly is exposed to both air and bacteria.
As a result of this the chemicals in the paint can form a suspension, whereby the ratio of liquids and semi-solids in the paint is disrupted, and you can get a skim on the top of the paint.
This isn’t always necessarily a problem, but sometimes the texture of the paint can become quite lumpy or even jelly-like, and this in turn affects the adhesion of the paint to the surface on which you want to apply it.
How Long Do Water And Oil Based Paints Last If Left Unopened?
Unopened alkyd and oil-based paints can last up to 15 years, while unopened latex and water-based acrylic paints can last up to 10 years.
They can often last almost as long once opened, provided that the lid is replaced after opening, and is kept tightly in place.
How Best To Keep Paint Pots To Prevent Them Going Bad Too Quickly
We recommend that you don’t open your paint pots until you’re ready to use them. That way, you can keep the paint in top condition for when you’re ready to get started with it.
Whether open or unopened, it’s always best to keep your paint in a cool but dry place.
This is because exposure to extreme temperatures can lead to such issues as freezing, condensation, and overheating, and all three of these have an impact on the paint’s constitution.
How To Tell If Your Paint Has Gone Bad
If you open your paint pot after a period of time and notice that a thin skim has formed on the top, this does not necessarily mean that the paint can no longer be used.
For instance, you can simply remove the skin, give the paint a good shake and a stir, and it can be ready to use once again.
However, if the paint is particularly lumpy or chunky in consistency, then this will not be usable.
But the best indicator that a pot of paint has gone bad is the odor. If bacteria has got into the paint, this can bring about a smell similar to sour milk, which can become quite rancid.
What’s more, if you were to paint a room with such paint regardless, not only does it have an offensive odor to begin with, but this will become progressively worse over time.
How To Make Old Paint Usable Again
Here’s how to revive old paint in order to make it usable once more.
Water-Based Paint
When it comes to water-based paint that has gone hard, you can often fix it simply by adding some water or solvent, allow it to this the paint, and then give it a good shake and stir to mix it.
If you’re still not happy with the texture at this point, you can gradually add more solvent and keep mixing until you’re happy with it.
Oil-Based Paint
One of the more common ways to revive oil-based paint is through the use of turpentine.
All you have to do is put the softened dried out oil paint into a container and add some turpentine to it. Turpentine oil is a paint solvent, and it will thin out the paint.
Just mix it in, and keep at the task until the paint returns to its required consistency, or as close as it will get.
Wrap Up
So, to summarize, both water and oil paint can go bad. But, if you keep them unopened and store them in a cool and dry place, then they can keep well for up to 15 years.
However, if you do open the paint, this will dramatically shorten its shelf life.
Bacteria can get in if the lid is not tightly replaced, giving it a sour, and rancid stench, and the ratio of solid to liquid parts can be disrupted, making the paint lumpy, which will make it less adhesive to the surface.
On some occasions, however, it can be possible to revive old paint, simply by adding solvent and giving the paint a really good shake or mix.
We hope that you’ve found this article helpful, and trust that you now know exactly what to do with any paint you get if you want it to last.
No task is too small. We can guide you and offer advice, no matter if you are filling in gaps in the wall, hiding cords, or simply fixing up construction mistakes. We love to help, and strive to do so in any way that we can.
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