You open a can of paint, and instead of the paint-y smell that usually wafts up, you get a whiff of sour milk. Gross.
Unfortunately, when paint smells bad, it is no longer usable. Bacteria is present in the paint, causing a sour smell that lingers even after the paint is dry. This is most likely to occur in paints that are over 10 years old, but bacteria can breed sooner if the paint is stored incorrectly.
So if you just opened a can of bad-smelling paint, you’ll want to toss it. But what if you’ve already applied the paint?
Don’t worry. There are a few things you can do.
Note: This blog contains affiliate links. If you click and make a purchase, I may receive compensation (at no additional cost to you.)
Why Your Paint Smells Bad
Every time a can of paint is opened, the paint inside is exposed to the bacteria of the outside world.
This happens when the paint is manufactured, when the color is mixed in at the store, and every time you open the paint to use it.
Since the world isn’t sterile, there’s not much you can do about it.
Most of the time, the bacteria is harmless to the paint, which is why sour paint isn’t a rampant problem homeowners face.
But occasionally, some harmful bacteria get in there and start breeding. Usually, it takes 10+ years for those bacteria to cause a problem, which is why modern latex paints have a 10 year shelf life.
But maybe the can was dented, letting in fresh air to help the bacteria breed. Or the paint was stored in extreme weather conditions during transit. Or maybe it’s just a stronger bacteria strain.
All of these things can cause the bacteria to breed faster than usual, resulting in paint that smells bad.
So if you’ve just opened a brand-new can of paint, and it smells sour, congratulations, you’ve won the bad-luck lottery. Maybe don’t go gambling today?
Instead, take the paint back to the store, and argue your case to get a fresh can.
How to Know if Your Paint is Bad
I’m going to try to keep this part short: if you’ve landed on this page because your paint smells sour, it’s bad.
Toss it, or if it’s new, take it back.
If you’re still desperately hoping it can be used, you can test the paint on a piece of scrap wood. Let it dry completely. Does it smell funny? If so, toss it.
If you can’t smell a thing… well, maybe you can use it. But you’re taking a risk, here. Painting a wall takes a lot more paint than scrap wood and that extra paint may make the stench strong enough for you to smell it.
I wouldn’t risk it, but we each have our own tolerances.
What to Do If Your Dried Paint Smells Bad
Okay, so maybe you ended up here after you already used the bad-smelling paint.
It’s okay. I get it. The paint looked fine, and you figured the smell would dissipate once the paint dried. And then it didn’t.
Don’t panic. I’m not going to say it’s an easy fix, but it’s not a hard one either.
Step 1: Wash the Walls With Bleach
Ultimately, we’re going to paint over the stinky paint, but first we’re going to try to kill as much of the bacteria as we can.
The CDC recommends mixing 1 cup of bleach with 1 gallon of water when clearing mold growth on hard surfaces, like floors and walls. Technically, this isn’t mold, but the concept is similar.
Put that mixture in a spray bottle, and wipe down your walls. Don’t dry the walls after – let them air dry. This will give the bleach time to work.
Step 2: Prime the Walls
Zinsser’s Shellac-Based BIN Primer is made for this situation. It seals smells so that they don’t reach the room.
It’s also really expensive, and you’re probably tempted to pick a cheaper primer. I get it. Don’t. It won’t work.
This post isn’t sponsored, and I’m not telling you this for affiliate sales or anything like that. In fact, most of the time I recommend their Zinsser’s oil-based primer, which is my absolute favorite.
But in this situation, you need the shellac primer. The oil and water-based primers will not seal the smell.
So once your walls are dry after the bleach wash, grab the shellac primer, and apply a coat just like you would a coat of paint.
If you’ve never worked with shellac products before, they clean up with denatured alcohol or acetone (not water,) so you’ll want to have some of that on hand as well.
Step 3: Paint the Walls
Once the shellac primer has dried (usually a 1-hour recoat time,) paint the walls.
Obviously, check and make sure your paint smells normal before you paint!
Storing Paint So It Doesn’t Go Bad
I mentioned earlier that improperly storing paint contributes to the paint going bad. Here are a couple of quick things to keep in mind.
Opening and Closing The Paint Can
When extra air gets into the can, that can increase the rate of bacteria growth.
This is why it’s really important that you open and close the paint can correctly. This is by using a paint can opener to open:
Usually the paint counter people will give you one of these with your paint purchase.
Also, you should use a mallet to close.
I know. Most people use a screwdriver and hammer, and are fine.
But screwdrivers and hammers are more likely to dent the can than paint can openers and mallets. Dents increase the risk of air getting in while the paint is in storage, and therefore increases the risk that the paint will go bad.
Temperature Considerations
Latex paint is water-based, and freezes at 32 degrees Fahrenheit. I did a whole experiment on this, but the short story is, you can’t really save previously frozen paint.
So don’t leave your paint in the cold.
But the heat matters too. Warm temperatures help bacteria breed, which will lead to your paint souring faster.
Store your paint in a cool (but not freezing,) dry place indoors to help extend its longevity.