When you're called upon to repaint a masonry surface, treat it as you would any other surface - at least in the sense that the performance of the coating you apply depends greatly on the condition of the existing coating. Carefully check areas that are fading, cracking, and peeling. Remove all existing paint that isn't in good condition. Efflorescence may be present, having worked its way through the existing film. It's not as easy to spot, but also may be present under the coating, where it can cause adhesion failure.
Telltale signs are areas that are bulging or peeling.
Either way, whether the efflorescence is on or under a coating, there's a moisture problem that must be corrected. If you've determined that the existing coating is sound and only has some surface chalking, then products such as Wonder Flow Masonry Conditioner from Harrison Paint Corp. in Canton, OH, can be used for treating mild chalking conditions. When using primers, sealers, and conditioning coatings, be sure you use the recommended topcoat with it. Selecting a basecoat to help solve a problem and then applying an inappropriate topcoat just trades one set of problems for another. Be sure you're using the right spray equipment.