To repair a cracked sink, clean and dry the crack, apply epoxy adhesive, let it dry, and sand it smooth. Oil ruins the epoxy bond, so avoid touching the crack after it is cleaned and dried.
Before applying epoxy adhesive, thoroughly clean the sink, and dry the crack with a hair dryer until it is bone dry. Wearing rubber gloves, prepare the epoxy adhesive according to the manufacturer's directions to use the right ratio. Add the epoxy resin in the correct ratio to the container, and then add the polyamine hardener. Mix for three minutes, scraping the bottom and sides as you go for a thorough blend.
Using a toothpick, apply the adhesive in the crack, and smooth flat. Allow the adhesive to dry for 24 hours before sanding it flat. If necessary, use appliance paint to touch up the area.
For a cleaner repair, use painter's tape along the sides of the crack to protect the area and plastic sheeting to cover the rest of the sink and counter. Remove the tape after sanding the resin smooth. To make sanding easier, use a razor blade instead of a toothpick when applying the epoxy. To clean spilled epoxy, use acetone or nail polish remover and a paper towel.