Historically we have shown in the composites industry that you can't
effectively "fill" gel coat cracks with another coating, or simply cover them
up. In examining the mechanism of gel coat cracking two issues become apparent:
In the case of hairline cracks, the inherent viscosity and surface tension
characteristics of most coatings will not allow them to penetrate the fracture
area. If the crack is large enough that a coating will penetrate the fracture
cavity, the bond strength between the coating and the crack sidewalls is not
sufficient to prevent the development of two new micro-cracks on each sidewall.


The only effective method of preventing crack propagation is to remove the
crack in it's entirety by sanding to the bottom of the fracture area.

The use of thermoplastic shrink film over a gel coated surface is an intriguing
idea. Tedlar, in particular, performs very well in long term outdoor exposure.
However, keep in mind that it would mask the cracks in the gel coat that
potentially could propagate into the laminate substrate. I would have the same
level of concern about hidden cracks in composites as I have with hidden
corrosion in metal aircraft.

Bob Lacovara