I know of wings on a Phoebus that was sanded and then sprayed with
Polyurethane.
After a couple of years, the wings looked like surface of El Mirage Dry Lake
in Southern California.
The old gelcoat pieces were not coming off but the cracks and fissures in
the paint were obvious to the most casual observer.
However, this Phoebus is still flying and it has been probably 15 years since
sprayed.
GA