Efflorescence is a white salty substance that forms on masonry and plaster due to moisture migrating through the surface. If left untreated for long periods of time, it will become hard and crusty. Any source of excessive moisture must be eliminated and the surface must be cleaned by scraping or wire brushing, and surfaces must be repaired where applicable before priming and painting. Surfaces can be painted with top quality alkyd or acrylic latex based primers and paints that are alkaline resistant