Surface prep for epoxy primer / filler grit query

[chamy]

Working on a fibreglass structure, I planned to 'key' the areas to be filled with 80 grit, apply the epoxy-based filler, then sand 120, then 320, then lay the epoxy primer / filler.

Are those grits OK?

 

[steveo3002]

id choose 180/240 , no point going too fine as you need a good key

 

[langy]

On GRP i like to fill glass with glass paste as filler tends to sink, I also epoxy prime before any filler is needed.
This is basically the process i use
Key the gelcoat with 80-120 grit, Apply epoxy primer, key epoxy with 150 grit, do filler work if needed, keep the filler thin, then epoxy again and go wet on wet with the hi-build primer, then flat with either 600 grit (straight paint) or 800 grit (COB) HTH