An application of thin liquid asphalt, most often MC-30 or MC-70 cutback or a penetrating emulsion, on a compacted aggregate base. It soaks a short way into the surface, plugs voids, waterproofs the base and gives the first lift something to grip. Prime needs time to penetrate and cure before paving, and any excess left standing on the surface gets blotted with sand.
Base passed density yesterday, prime goes down this afternoon and the paver comes in on top of it Monday.
Plenty of full-depth and thick-lift jobs skip prime entirely, so asking whether the job is primed is a spec question, not a rookie one.
Also heard as
- prime
Related terms
Tack coat
A thin spray of asphalt between layers that bonds the new lift to the surface underneath.
Cutback asphalt
Binder thinned with a petroleum solvent so it flows at low temperature, then hardens as the solvent evaporates.
Asphalt emulsion
Asphalt binder broken into tiny droplets and suspended in water with an emulsifier so it can be sprayed cool.