Home Problems & Solutions White stains and salts have appeared. Exterior Wall Painting CausesNon-carbonated plaster was usedThere is trapped moisture or rising damp.SolutionAllow the newly plastered surface to mature and the wall to dry.If there is rising damp, seal the surface with special sealants and fill in the cracks.Then prime.Apply two coats of paint from the 4 SEASONS family.