The Coating is too Thick
If paint is applied too thickly, the surface of the paint can dry, while the paint under this dry skin remains wet. As the dried layer expands and contracts it develops a web of wrinkles. This is more likely when using oil-based coatings as they can easily be applied too thickly.
First Coat has not Dried
Wrinkling can also occur when a second coat is applied too quickly, without allowing the necessary drying time for the first coat. The upper coat becomes a dried film preventing the lower coat from drying properly. This is also true where a topcoat has been applied before a prepcoat has dried sufficiently.
High Heat, Low Humidity
Temperature extremes can also cause wrinkles. Painting outdoors in high temperatures can cause the paint to form a dry skin before the entire coating has dried. When humidity is extremely low, the dry air will suck the water solvent from the water-based paint quickly causing a skin to form.
High Humidity / Ambient Moisture During or Shortly After Drying
Exposing a water-based paint film to dew, high-humidity or rain shortly after the paint has dried can also cause wrinkling and failure of the paint system. When the paint is touch dry, there is still a significant amount of solvent yet to be evaporated before total curing is achieved. At this stage, ambient moisture can return into the coating and cause it to wrinkle. This is generally only an issue with water-based paints as oil-based paint solvents are not as susceptible to moisture.
The Substrate was not Cleaned and Prepared Properly
Wrinkling can also be a result of painting over contaminated surfaces that contain dirt, oils and waxes. These contaminants can cause the coating to react and deform in areas where the contaminants are present.