St. Louis Asphalt Road Construction

Tack coat — typically SS-1h, a thin asphalt emulsion — is applied between pavement layers to promote bonding. On an overlay it’s the difference between two layers acting as a single pavement structure and two layers that delaminate, slip, and shear apart under traffic. Tack is required on vertical edges at tie-ins with existing pavement, on the surface of any existing asphalt or concrete prior to overlay, on base mix that was installed more than three days prior, and on any base mix that has been rained on.

For commercial overlay projects and mill-and-overlay work, tack coat is non-negotiable — see how we approach this on our St. Louis asphalt maintenance page and road construction page.

Prime coat (typically MC-30, a cutback of asphalt cement blended with a petroleum-based solvent) is designed to penetrate granular base material — crushed stone or stabilized subgrade — to bind the surface, reduce dust, seal against moisture, and improve adhesion to the asphalt layer above. It can be valuable on certain DOT and heavy industrial projects.

For most commercial and private paving work, however, the trade-offs outweigh the benefit. MC-30 requires undisturbed cure time most jobsites can’t accommodate, and it tracks across the site on tires and boots once any work resumes. On Byrne & Jones commercial paving projects, we typically rely on properly compacted, well-graded aggregate base plus tack at tie-ins rather than prime coat. For a deeper look at how we build a parking lot or roadway from the subgrade up, see parking lot construction and road construction.