Although fiberglass shower stalls are generally resistant to most impact damage, it's likely that they'll develop cracks and other irregularities over time. In these cases, the structural integrity of the shower stall may be compromised. Rather than hire a professional contractor to make repairs, you can repair the cracks to the doors on your own. This process requires minimal time and can be done with a few tools and materials that are all available at most local hardware stores.
Widen the Fissure and Cut a Groove
If the crack in the shower stall is small to moderate in size, you'll actually need to widen the crack before you begin in order to achieve the smoothest appearance with the epoxy. That has to do with the amount of epoxy that you'll need to fill in the crack. If there's not enough epoxy, it's difficult to smooth it so that it blends in with the rest of the fiberglass. Pull apart the fiberglass at the site of the crack by hand. You can then use the tungsten carbide groove cutter to cut a deeper groove into the crack.
Use the plastic applicator that comes with your epoxy set to apply the epoxy to the grooves and cracks in the fiberglass. Mix the epoxy well before you apply it. Work quickly to ensure that the epoxy doesn't set before it's completely pressed into place.
Once you've applied the epoxy to the crack you can use your hands to carefully press the epoxy down into the fissure. Doing so will help to ensure that the epoxy completely fills in the crack and that the shower stall is as secure as possible.
Sand Down the Epoxy
If you've made any errors in the epoxy, use the wet/dry sandpaper to sand it down before it sets. Doing this will create a smoother product later on. Look in particular for any parts of the epoxy that are sticking up from out of the base of the crack.
Allow the Epoxy to Dry and Make Final Touches
Allow the epoxy to dry overnight. Return when it's dry and examine the crack. Do some final touching up with the 400-grit sandpaper to ensure that the epoxy is blended into the surrounding fiberglass of your shower stall as cleanly and easily as possible. If you need more epoxy, you can apply an additional coat.