The Purposes of a prime coat are to protect the base course from the weather and increase the bond between the base and the material, preventing thin lifts from slipping. This item is used for pervious surfaces such as earth, aggregate base or cement treated base over which a seal coat or bituminous mixture less then 4 in. thick is to be placed. Generally SC-70 or SC-250 liquid asphalt is used. The base course will absorb the prime more rapidly and completely if its surface is damp. However, excessive water must not be used and free water should not be standing on the surface of the base course.