Although bathtubs are designed to be durable, cracks can appear if you or your kids accidentally drop something on the surface. Even if your crack isn’t causing a leak, you should fix it immediately to make sure it doesn’t expand and get worse. Although plastic bathtubs are cheap when compared to bathtubs made from other materials, replacing them isn’t always a viable option.
Drill a 1/4-inch hole on each side of the crack. This will prevent it from getting any larger.
Lightly sand down the crack with 120-grit sandpaper. Don’t sand too much or too hard, otherwise you could scratch the surrounding plastic.
Clean the cracked area with a damp rag to get rid of any loose dust and debris. Leave it to dry for at least 12 hours. If you’d rather not wait, use a hair dryer to get rid of any moisture. If the crack is damp, the epoxy resin won’t bind to the bathtub.
Mix the two parts of the epoxy resin according to package directions. Fill the crack with the mixture. Make sure it’s flush with the surface by scraping off the excess with a putty knife. Leave it to cure for at least 12 hours.
Sand the crack with 240-grit wet/dry sandpaper. Soak the sandpaper in water and then sand over the crack again.
Clean away the dust and debris with a damp rag and then wait for it to dry -- at least 12 hours.
Apply a thin layer of gel coat enamel with a nylon-bristled paintbrush. Wait for it to dry -- at least four hours -- before you use your bathtub.