For flexible pavements, the graded subgrade or the top granular base layer may be prepared with a prime coat. A prime coat is a sprayed application of a cutback asphalt or asphalt emulsion (AE) applied to the surface of untreated subgrade or base layers. The prime coat serves several purposes:

The project plans specify the rate at which the prime coat is applied, and rates will vary from one project to another. Generally, however, medium curing cutback asphalt is applied at a rate between 0.2 to 0.5 gal./SY, and emulsified asphalts are applied between 0.1 to 0.3 gal./SY. For emulsions, it is recommended to cut-in the emulsion with the top 1 in. of the base. Alternately, cutting in 50% of the prime into a surface of cement-treated base, followed by compaction and application of the remaining 50% has shown to be beneficial in bonding of subsequent bituminous layers.