To resurface a plastic bathtub, thoroughly clean the tub, sand it down until smooth, and then apply epoxy with a paintbrush and a small roller. Done correctly, this creates a smooth, waterproof surface and freshens up the bathroom.
Before starting the job, make sure that the bathtub is very clean by using an abrasive cleaner to remove any stains or anti-slip strips. Use a degreaser to remove any residue. Sand down the entire surface of the tub with 400- to 600-grit sandpaper, keeping it wet throughout. This both removes any remaining dirt and creates a roughened surface for the epoxy.
Once the preparation is complete, rinse away any dust, and dry the tub thoroughly. Mix the epoxy according to the instructions on the packet. Using a paintbrush of around 3 to 4 inches in width and an appropriate roller, apply epoxy to the surface of the tub. Try to keep the brushstrokes in a single direction, and apply the epoxy in two thin coats, allowing about an hour in between to allow the first coat to dry. Feather the brushstrokes at the edge of each stroke to avoid hard lines in the finish. Finish the job by caulking the tub around the edges, and freshen the caulk around any abutting tiles.