1. Bubbles 1.caused by air
  The air that has not been expelled from the gel coat surface layer will burst under the condition of being heated (such as being exposed to sunlight), resulting in damage to the gel coat layer.

Based on the phenomenon that the inside of the bubble is dry glass fiber, it can be simply determined that the bubble phenomenon is caused by the unexpelled air.

2.Bubbles caused by solvents/curing agents
   When applying subsequent laminations during the lay-up process, if the curing agent or solvent directly drips onto the surface of the already cured gel coat, the droplets will be encapsulated and form bubbles at the interface.
 After these bubbles burst, there will be an odor of the encapsulated curing agent/solvent. This can be identified by the smell.

3.Surface Bubbles

 Surface bubbles generally occur during the use of the product. This kind of bubbling phenomenon does not directly occur in the gel coat layer, but rather in the subsequent fiberglass laminations. Water droplets in the subsequent laminations form bubbles and migrate towards the gel coat layer.

4.Bubbles caused by incompletely cured resin
  If there is incompletely cured resin in the gel coat interface layer, it will form bubbles which will burst and cause damage to the gel coat layer.
 These bubbles are composed of resin that has not been completely cured, and can be identified by the smell.