Tub and shower inserts are typically durable surfaces that can withstand a lot of abuse, but they can become dingy or turn yellow over time, especially if they are white. If you have a bathroom with an insert that is no longer looking its best, or in a color that you don't care for, you can paint the plastic to make it new again or give it a new look.
Clean the shower or tub as best you can with a bathroom cleaner and sponge. Scrub the surface to remove any soap residue, mildew and other buildup.
Rinse out the tub to remove the cleaner. Let the tub completely dry. You can towel dry it to speed the process, but even then you won't completely get every bit of moisture. If you towel dry, wait at least two hours before proceeding. If you don't towel dry, wait four to six hours.
Sand the entire surface of the bathtub or shower with the sandpaper included in the refinishing kit. This is meant to rough the surface so that the primer will adhere better. Look over the surface to ensure that you didn't miss any spots.
Roll on the bonding agent over all flat surfaces of the tub, and use a paintbrush to get into corners and shelf areas. Let the bonding agent dry before proceeding. This will take several hours. Follow package instructions. Paint on the primer coat after the bond dries, and then wait for it to dry as well.
Paint on the first coat of tub paint from the kit. The kit comes with two separate coatings, and indicates which is to be used first. Let this dry based on the recommendations of the kit.
Paint on the second coating. This is a sealant coat that gives the surface a shine and creates a waterproof barrier. Let this dry for the recommended amount of time as well.