Dear Arup Ray
Tips;-• Dry out the new wall surface. • Old surface should be free from loose, powdery particles by scraping. • Water based cement primer after thinning with water, apply on the surface after filling the minor cracks and defects. • Apply wall putty after the first coat of primer.• Rub the surface with emery paper to smoothen the surface.• Apply the final coat of primer on putty surface.