15 March 2001
SPRAYED ASPHALT SURFACE TREATMENTS
4.1. Prime Coat. A prime coat is a spray application of bituminous material applied to the
surface of a base course which is to be covered with a pavement layer. The purpose is to
waterproof and prevent raveling of the base during construction and to form a dense base to
which a bituminous pavement will adhere. Materials that can be used for prime coats are listed
as follows: RC-70, MC-30, MC-70, or SC-70 cutback; SS-1, SS-1h, CSS-1, or CSS-1h emulsion.
4.2. Procedural Steps (Prime Coat). The following steps should be conducted to apply a prime
4.2.1. Prepare the surface. The surface shall be free of all loose material such as dirt, clay, dust,
or any other undesirable material. A light brooming should be used to remove these undesirable
materials. If the base is excessively dry, it should be lightly sprinkled with water.
4.2.2. Apply the prime. If the area to be primed is large, a distributor should be used. Prime coat
applications on smaller areas can be sprayed with a handspray wand. Prime coat application
rates are 0.10 to 0.25 gallons per square yard (0.45 to 1.13 liters per square meter). The entire
area shall be coated.
4.2.3. Allow prime to cure. Prime coats shall be allowed to cure for as long as necessary.
Curing time can be up to 48 hours. If there is excess prime, it should be blotted with fine sand or
4.3. Problem Areas (Prime Coat). A major problem is overpriming. Application rates should be
tested prior to priming. Proper nozzles and settings on the distributor spray bar or handwand
should be checked. Nozzles should be checked to ensure they are not plugged and nozzles