Primers are first coat on bare surface to give good adhesion to subsequent coat. Sealers help convert the porous surface into non- porous so reduce over-consumption of topcoat for stronger bonding of subsequent coats. Undercoats are intermittent coats for better adhesion and forms protective barrier to prevent chalking & breakdown of paint film due to saponification. It can be used on new plaster, concretes, asbestos or any other substrate. Good on interior (new / old) surfaces with best Inter-coat adhesion.