It was over a year ago that we bought latex paint for the dining room in our 1915 Foursquare, but put off the project. When we opened the cans, the paint smelled like sour milk. Figuring that modern paint can’t “go bad” and that the rancid smell would dissipate when the paint dried, we used it. It’s been two weeks and despite tons of ventilation, it still stinks! —Frank and Anna Taylor
Make no mistake—if paint smells bad, it is bad and should be discarded. Most latex paints have a shelf life of up to 10 years, but paint can go bad in a much shorter window of time, especially if it’s not stored properly. Bad paint may not go on properly, leaving a visibly rough finish that also may peel.
The most common culprit in stinky paint is bacteria, which can be introduced into the paint at the factory, or when tints are added at the hardware store, or when a can is partially used and then stored. Low- and zero-VOC paints are especially vulnerable because they are low in solvents that not only help stabilize paint, but also counteract bacteria.
To determine whether a can of paint is still usable, pry off the lid with a screwdriver and smell the paint. Good paint will have a chemical smell, but it won’t smell rancid like yours did. Obviously, if the paint is moldy on top, discard it immediately. If the paint has begun to separate, with liquid on the top and the denser paint pigments below the surface, mix it up with a stirring stick. If it blends together smoothly, it’s okay to use. This is true even if you have to remove a thin skin from the top of the paint. If there’s any sediment in the bottom that won’t blend into the rest of the paint, discard the can.
For paint that dries and still has a persistent smell, try washing the walls with a mixture of 1 part bleach to 10 parts water, then rinse with plain water and a clean sponge. Allow the walls to dry completely. Follow with an odor-sealing primer, such as Kilz (kilz.com) or BIN Advanced (rustoleum.com), a synthetic shellac sealer. You may need to apply two coats before repainting with fresh (unspoiled) paint.