Prime Coat History

Prime coats have long been used to seal the surface pores in the base, thus reducing the migration of moisture and absorption of the first application of surface treatment binder, strengthen the granular base near its surface by binding the finer particles of aggregate, help protect the base from inclement weather and limited vehicular traffic before the next pavement layer is constructed, and promote adhesion between a granular base and a subsequently applied bituminous surface by precoating the surface of the base and by penetrating the voids near the surface.  There is no definitive answer to how long prime coats have been used but it is widely believed that prime coats have been used ever since the industry started using macadam as a pavement surface in the early 1900s.