Scrap the previously painted surface to remove loose or flaking material and paint, dust grease, dirt or powdery material by thorough brushing. Any previous growth of algae, fungus or moss, chalking etc. needs to be removed using wire brush and cleaned with water. Treat the infected surface with a mild solution of household bleaching powder solution (recommended proportion 2kg to 50 Its water), leave it for 24 hours and then wash the surface with clean water. Surface should be clean, dry and free from efflorescence. Bigger cracks should be filled using cement & sand mixture in the ratio of 2:3. Fill the smaller dents with TATA Wall Plus Putty and smooth the surface with sandpaper.