What is the difference between tack coat and prime coat?

Tack coat is a thin bitumen application between two asphalt layers (for example, between a binder course and a wearing course) to ensure they bond as a single structural unit rather than delaminating under traffic. Prime coat is applied to a prepared granular base or sub-base layer before the first asphalt layer is placed, sealing the surface and improving adhesion for that first layer. Both use the same distributor equipment but typically at different application rates.