Cracking in clear coat is almost always due to environmental or application issues, such as:
  • Temperature differential between the body panel and the clear coat that is getting applied. 
  • Environmental conditions such as excessive heat or humidity during application and curing.
  • Application issues such as spraying too much material in full wet coats can lead to cracking, or applying clear coat to heavy base color coats that haven't fully cured can cause cracking in the clear.
These questions will help you investigate how this happened. 
 
1. Did the clear coat develop the cracks or a hairline spider web effect almost immediately as the clear coat flashed off? If so, then it is most likely a temperature differential between the body panel and the aerosol can temperature. The body panel and the clear coat have to be at the same temperature, and over 65 degrees Farenheit.
 
2. Did the clear coat go on okay, and then after a week or a couple months, did it developed the cracks? This delayed reaction may indicate that it didn't cure properly, either because of a too heavy a coat, or it was applied in higher humidity, or at too low a temperature (even if both the body panel and the clear coat were at the same temp, they have to be warmer than 65 degrees). When this happens, the cracking can appear after a sudden temperature change (such as taking the car outside in cold weather).
 
Because of that, it may be safer to wait and apply the clear coat when the outside temperature is over 65 degrees F. When the tempuratures are cold, a 2K clear coat like SprayMax Glamour Clear will harden faster due to the two part hardener/activator in the can and that may prevent the cracking. However, temperature differentials can still cause cracking with a 2K clear.
 
How to fix a spider web cracked clear coat job. 
Unfortunately, fixing the spider webbed clear coat requires sanding the finish down until the cracks can't be seen or felt by hand. Clear coat can be wet sanded, and sometimes, if the body panel is large, this is best done with an orbital sander. After the clear has been sanded smooth, it may require additional base coat, depending on whether the base coat was exposed or removed when the clear coat was sanded. The next step is then to either re-spray the base color, or clear it again.