Causes:
Thickness is too high which leads to an external drying while the solvents are trapped in the paint film.
Paint is sprayed over wax, oil, and grease.
Drying in bad conditions: Workshop is too cold, humid and non-ventilated.
Bad application conditions: Not enough air circulation and/or heat.
Not enough flash off time.
Too much retarder used.
Incorrect hardener or mixing ratios.
Preventive measures:
Clean surface thoroughly before painting.
Avoid thick layers.
Improve spraying and drying conditions (heat, air circulation, etc.).
Allow enough flash off times.
Use recommended hardener and thinner and observe mixing ratios.
Remedy:
In general, it is possible to remedy a slow drying problem by moving the vehicle to a place where the ventilation and the temperature are more appropriate or by heating at a moderate temperature (unless the problem is due to the use of a wrong hardener or wrong mixing ratio of hardener – non stoichiometric ratio). If the problem is due to very thick layers, “des rides” may show, except if special care is taken during the heating phase.