(or Perhaps in the Other Weather Conditions When You Painted)
How can that be? The answer, my friend, lies in the chemistry of these paints:
The particles of acrylic binder in latex paints are "thermoplastic", so they harden as the temperature drops. If the temperature is too low when the paint is applied, it can fail to produce a good paint film. And that can lead to early paint problems.
What’s more, paint film can be affected by falling temperatures in the hours after the paint is applied. It actually takes about 36 hours for paint to form the best protective film, even though the paint may be dry to the touch much sooner. So, a quick drop in temperature right after painting can be harmful to paint.
It isn’t just cold that can affect newly-applied paint. Very hot temperatures can also compromise the job by causing the paint to dry too quickly. When that happens, the binder particles lose "mobility", get locked in place, and don’t have enough time to form a paint film with optimum durability.
A related point: Paint film formation isn’t affected just by the air temperature; it also can be affected by the temperature of the surface that is being painted. An exterior wall getting full sun on a bright, summer day will be considerably hotter than the ambient temperature. If it gets too hot, that can cause the paint to dry too fast.
Windy conditions are another factor that can affect exterior latex paint. Like high temperatures, wind can also cause paint to dry too quickly and compromise the long-term performance of a paint job.
So much for problematic weather. What are the best conditions in which to do exterior painting? Generally speaking, when temperatures are above 50°F. and below 90°F., on days that are not extremely windy.
There are also ways to combat weather that is less than ideal. Rather than painting the sunny side of the house on very hot days, work on the shady walls or other areas out of direct sunshine. Likewise, on moderately windy days, focus your efforts on the sheltered portions of your home. And if conditions are just too extreme to apply paint, turn your attention to caulking or other types of surface preparation.
Finally, before you conclude that it’s just too hot or too cold to paint, check the label on the paint can. Paint manufacturers are always working to improve their products so that they can be applied in a wide range of temperatures. You might just discover that your paint finds "questionable" weather just peachy!