Prime Coat : Prime coat is an application of low viscous cutback bitumen over an existing porous surface like WBM base course. The main objective of priming is to plug in the capillary voids of the porous surface using a low viscosity binding material. Mainly Medium Cutback and slow cutback are used. Tack Coat : Tack Coat is a very light application of asphalt, usually asphalt emulsion diluted with water.the application of asphalt over an existing impervious pavement surface which has already been treated by a prime coat. Tack coat is generally of higher viscosity. Seal Coat : Seal coat is a thin surface treatment used to water-proof the surface and to provide skid resistance.