"B Lacovara" wrote in message
...
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


If the 'process' was to first remove the cracks by sanding back to the
substrate, then fill and flat locally with a polyester filler and then to
apply film to the entire surface then perhaps we might have a solution?

The biggest time consumer I find is the manual flatting and polishing
required with either Gel or paint finishes.

Ian