Filler or Gelcoat

[Pacman1972]

A quick question for the GRP experts among you.

I am doing a small fibreglass repair where the wing mirror attaches to the door (nothing major).

Having read up it seems the general advice is repair the damaged area with 300gsm fibreglass/resin and then smooth the surface with ISOPON P38 filler before sanding, priming and painting.

As the cars came from the factory with a gelcoat, I'm curious as to why the general advice isn't to smooth out using gelcoat instead of P38.

My instincts are telling me to go with gelcoat to be as close to factory as possible.

Thoughts?

[Hawkshaw]

AIUI gelcoat won't set properly unless it is in a mould, so for a repair it is advisable to use filler.

[rev-erend]

As a rule of thumb, I would try an use resin to make the repair if it is shallow or can be built-up / sanded down rather than any filler
as they do tend to crack but if its deep then filler is the way to go.

A picture would be useful.

[plasticman]

You need a thin boundry between the fibreglass repair and the paint to stop the glass strands showing through . You can use filler or gelcoat but the surface of the gel in contact with air should remain tacky but these days that doesn`t last long . The gel is a better job but much harder to sand down to a good finish and probably unnecessary .