Pavement Surface Preparation for Prime Coat
Posted by Jesse Willoughby on Sun, May 10, 2009 @ 05:11 AM
A good prime coat requires a base course surface thatis smooth, properly crowned, and free from
wash boarding, ruts and standing water. This must bechecked immediately before the prime coat is applied.
On very tight, dense bases sweeping with a power broommay be needed to remove a dust seal that has built up under traffic. More oftenthe base is “tight bladed” with a motor grader. This slightly loosens thesurface, which helps the prime penetrate. It also removes any loose rock.
As with tack coats, the worst enemy of a prime coat isdry dust. The surface of the base course should be slightly damp (notwet) for the prime to penetrate properly. Dry dust can be eliminated with alight fog of water sprayed under high pressure from a water truck. Whether towater, and how much to water, is a decision which must be made by theinspector. This decision is based on how moist the grade is, how hot and sunnyit is and how soon it will be primed. Too little moisture and the prime willnot penetrate; too much and it will puddle up or even run off the grade.