Does Emulsion Paint Go Off?

So, there’s a room in your house that needs freshening up. Maybe your children have combined rooms and now you have the opportunity to get back to your office. Or maybe you want to make a playroom or nursery.

Yes, emulsion paint can go off and leave a nasty smell in the room you are painting. You need to be sure your paint is fresh and usable.

We all want to do our part to reduce waste and use what we have available. So, in this article, we’ll take a look at ways you can tell if your paint has gone off, how long you can expect the paint to last, and where to store paint in your home to get the longest use out of it.

How to Tell if Your Paint Has Gone Off

There are several ways to tell if your paint has gone off, and you can think of them as a process that starts from when you first see the tin of paint in your garage to when you do a test roll on a piece of cardboard.

The Tin

Give your paint tin a look. One of the reasons your emulsion paint will start to go off is because bacteria are eating the paint and giving off gases. This will cause the paint tin to swell and the lid to bulge. If you see this, then right away you know the paint’s off.

But let’s say the tin looks normal. Take a closer look and check for rust, especially inside the tin, like on the bottom of the lid. This can mean air has gotten into the tin. Also, rust can cause metal bits to flake off into the paint. If that’s the case, don’t use the paint.

The Smell

Once you have started inspecting the inside of the paint tin, check carefully with your nose. Bad paint will smell like sour milk. It can also give you a bad gut reaction just as when you smell milk that has gone off.

The Look

The paint that has gone off has a particular look to it. It will appear watery, as though the pigments of the paint have all settled to the bottom. Similar to sour milk, it will look lumpy. It may also have mould or mildew on the surface.

Now, it’s common to see a degree of separation in paint that has been sitting for a while, as well as a thin, rubbery layer on the surface. Try stirring the paint. If it blends smoothly and stays blended for 10 to 15 minutes (and there isn’t a bad smell), then your paint is probably fine. Bad paint won’t blend together.

The Test

If the previous standards all check out, and you’re still concerned, the last thing to do is roll a test strip of paint on a piece of cardboard or old newspaper. If the paint rolls out smoothly, use it. If you see lumps and debris in what you’ve rolled, don’t use the paint.

For a visual example, take a look at this YouTube video of a painting contractor inspecting an old tin of paint. Primarily you’ll see an example of how bad the smell can be (don’t worry, it’s not gross), but you’ll probably notice a couple more signs that we have discussed.

What Causes Emulsion Paint to Go Off?

When emulsion paint goes off, it’s not a sign that the paint was poorly manufactured. It’s just what eventually happens.

Emulsion paint starts to go off when air gets into the tin and starts to change the chemical makeup of the paint.

Bacteria is another thing that can cause the paint to go off and it can be introduced into the paint when it is manufactured, mixed in the store, or used at home. Paints with low or no VOCs (volatile organic compounds) are more susceptible to bacterial growth because VOCs stabilize paint and repel bacteria.

How Long Can You Expect Emulsion Paint to Last?

The simple answer is probably not as long as you think. If you’re planning a repainting project and you realize it’s been 6 years since you’ve used that paint in the shed, just toss it and go buy new.

To answer this question more thoroughly, we have to look at a couple of variables. If your emulsion paint is unopened, one website reports that it can stay usable for up to ten years (provided it’s stored properly).

If you’ve opened your paint and are wondering how long you can keep it around, that’s another question.

One DIY website says that up to 6 months is about where the cutoff could be, another website says to use up your leftover paint within 2 years. Both qualify that storage and temperature are critical variables. Also, paint can go off within those times, so it’s always good to check.

What is the Best Way to Store Paint?

The best way to ensure that your paint lasts as long as possible is to store it properly. When you are done painting, seal your paint tin as tightly as possible to keep air from getting in. Keep the following tips in mind:

  • Wipe up any excess paint that spilled in the grooves that may prevent a tight seal.
  • Tap the lid shut with a rubber mallet. A hammer can dent the metal possibly causing a break in the seal.
  • If you don’t have a rubber mallet, use a block of wood against the lid as a buffer for the hammer.
  • Stack paint tins on a shelf. Moisture from the floor can cause rust.

Source: Lowes

Paint is adversely affected by extreme changes in temperature. Very hot or very cold, especially if frozen, can damage the paint.

This means that the two most common places that you would think of to store paint, the garage, and the shed, are out of the running. The dead of winter and the height of summer is going to be too much of an extreme in those places.

So, your options are rooms in the house, somewhere that is cool, dry, and dark. Safety is a factor if you have kids, so find a closet that is lockable or not used often. But stay away from your indoor furnace or water heater.

If you have a temperature-controlled basement, that is a good option. Or you can use the room under the stairs.

What is the Best Way to Dispose of Bad Paint?

If your emulsion paint has indeed gone bad, you need to throw it out. Be sure to check with your city’s environmental regulations first. Some areas may be stricter about paint disposal than others, especially oil-based paints.

But the generally accepted method goes like this:

  • Combine your bad paint with an equal amount of cat litter.
  • Allow the mixture to harden.
  • Throw it in the rubbish bin.


So, before you get going on your painting project, remember to check those left-over tins in the garage. It’s always good to avoid waste and work with what you have, but not if the emulsion paint has gone off. Painting with bad paint isn’t worth the nasty smell it leaves behind.

If the paint is bad, toss it and budget for new paint. And if you end up with new paint that is leftover from this project, be sure to store it properly for next time.




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