The prime coat is a coating of a binder onto a compacted granular base prior to application of
subsequent courses. Prime coats are generally applied to improve pavement’s binding to the
untreated aggregate base, and help the performance of the base if it is going to remain exposed to the weather for at least seven days or if it is going to carry traffic before HMA paving.
The main purpose of providing a prime coat is to prevent water from penetrating into the base, thus waterproofing the base and improve the strength of the base.