A light application of asphalt, usually a slow-setting or trackless emulsion and sometimes hot PG binder, sprayed on an existing pavement or lower lift right before paving. Its job is to glue the layers so they bend as one unit, since a debonded overlay slips, shoves and cracks early. Residual rates run a few hundredths of a gallon per square yard, heavier on milled surfaces and lighter on fresh mat, and the film must be even with no streaks or puddles.
Shoot the tack edge to edge and two inches past the paint line, inspector's already out there with the pans checking the rate.
Haul trucks tracking tack off the job on their tires is an inspector's favorite complaint, which is why trackless tack products exist.
Also heard as
- tack
- bond coat
Do not mix it up with
- Prime coat: Prime soaks into an unpaved granular base; tack is a thin bonding film between asphalt layers.
Related terms
Asphalt emulsion
Asphalt binder broken into tiny droplets and suspended in water with an emulsifier so it can be sprayed cool.
Break
The point when an emulsion's water separates and the asphalt droplets fuse, turning the film from brown to black.
Prime coat
A low-viscosity asphalt sprayed onto granular base to soak in, seal it and bind loose surface particles before paving.
Shoving
Localized bulging and sliding of the asphalt surface where traffic brakes, turns or accelerates.