The label instructions on every can of latex paint clearly state Do Not Freeze. Freezing can indeed ruin paint. However, some latex paint may be salvageable after freezing, because certain additives control freeze-thaw stability. Previously frozen latex semi-gloss paint can sometimes be used. Whether the paint survives freezing depends on how many times it has been frozen and thawed.
How Paint Freezes
Latex paint is made up of a number of components and additives suspended in liquid solvent. The solvent for latex paint is water. When water freezes, it expands. When water in paint freezes and expands it can damage the molecules in components such as the pigments and synthetic binders. When the paint thaws, the molecules may remain irreversibly damaged. Some paints have propylene glycol (also a component in automotive antifreeze) added for flexibility and protection against freezing.
Assess the Paint
According to several paint companies, including Sherwin-Williams, many paints can survive at least one freeze-thaw cycle without harm. It's fairly easy to tell if the paint has been irreversibly damaged. Thaw the paint, open the can and stir it. If it appears smooth and creamy like new paint, it's probably fine to use. If it has separated and can't be smoothly mixed, or if there are lumps and a grainy appearance to the paint, it should be discarded.
Risks of Using Previously Frozen Paint
According to Professor Frank N. Jones of the Coatings Research Institute at Eastern Michigan University, even if previously frozen paint appears all right, freezing has made it more brittle and it may crack and peel sooner than unfrozen paint when exposed to sunlight. The gloss of the paint can also be affected, he warns. Semi-gloss latex paint may have a lower sheen, or uneven gloss if it's been frozen.
Considerations
Since there are so many different formulations and grades of latex semi-gloss paint, contacting the manufacturer directly would be the wisest choice. Manufacturer phone numbers are printed on every paint can label, and you should be able to talk to a coatings scientist. Material Safety Data Sheets (MSDS) can be found on each manufacturer's website for extensive data on the paint formula.
It would appear that the only risk from using previously frozen semi-gloss paint inside the home may be lower or uneven sheen. Using the paint on the exterior of a home where it's exposed to sunlight could cause it to fail earlier than it should.
Expert Insight
Paint technology has advanced in recent decades, with latex paint providing better performance than ever before. In the early days of latex paint, it was not unheard of for painters to add automotive antifreeze to paint so they could paint in colder temperatures or leave paint on a cold job site. Modern paint is much improved and there are now paints that can be safely applied at any point just above freezing.
However, because there is insufficient data and conflicting information on the effects of freezing on paint, most professional painters would not take the risk and would get new paint for the job.
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