Before the final layer of paint is applied, steel doors should be painted with rust-resistant latex or an oil-based primer. Once this foundation has dried, most types of paints are compatible.
New steel doors often come pre-primed, which makes the process of painting the door simpler. Used doors, however, likely need more thorough priming. Doors that already have a layer of paint might need to have the paint removed first, as flaking is common when new layers of paint are applied to steel. While a primed door can handle a wide range of paint types, paint choices should take into account that doors are frequently touched and may experience significant temperature changes if the door leads outside of a structure.