Clean the affected mortar with a masonry cleaner, which is a mild acid, and rinse well. Follow the manufactures cleaning and safety recommendations. An alternative is to use TSP, trisodium phosphate. While cleaning use a nylon scrub brush to loosen any heavy build-up.

You will need to prime the brick and mortar. I would use Sherwin Williams Loxon Masonry Primer, it can handle high PH conditions. After priming you can use any good interior acrylic house paint.