A prime coat is the application of a suitable bituminous binder applied to a non-bituminous granular base as a preliminary treatment before the application of a bituminous surfacing. The prime coat is designed to perform several functions including:
- To promote adhesion between a granular base
- To help seal the surface pores in the base, thus reducing the migration of moisture and preventing the absorption of the first spray of surface binder
- To waterproof the base
- To help strengthen the base near its surface by binding the finer particles of aggregate
- To provide the base with temporary protection against the detrimental effects of weather and light traffic until the surfacing can be constructed
The most common cationic emulsion bitumens used for prime coat are CSS-1 and CSS-1h, whose application temperature is 10-60 ˚C and the amount of the used bitumen is 1.5-2.5 Kg/m2. Also, asphalt cutbacks RC-70, RC-250, MC-30, MC-70 and MC-250 are used with application temperature of 50-70°C depending on bitumen type and the amount of the used bitumen 1-2 Kg/m2.