ok i am repairing fiber glas fenders and a front bumper the fenders are new an i am preping for paintso to fill in cracks do i use regular bondo what do i use to get them smooth as glass

 

bump

 

The proper way to fix fiberglass is one of two options, cut out everything that's cracked and lay more fiberglass inside the area. Or second option is to cut it out, and fill it over with dura-glass/kitty hair/tiger hair. Depending on the size of the repair.

Just to prep it for paint, you should follow the paint manufacturers recommendations for substrate preparation. If you don't know what they are, I would wetsand with 600 to get it super smooth.

 

its a crack thats very tiny i mean i didnt notice till my first coat of primer