Bond/Tack Coats and Primers
In order to improve the bond between layers of pavement, a tack coat should be applied. A tack coat is very inexpensive insurance to improve the structural integrity of the pavement layer. There are many different types of tack coats and emulsions.
A bond coat is a spray application of asphalt emulsion. It is applied to an existing asphalt or portland cement concrete surface prior to a new asphalt overlay or patching. This eliminates slippage planes and provides a better bond between new and existing pavement layers.
A prime coat is a single application of either a specially formulated asphalt emulsion or a low-viscosity asphalt cutback. Their primary functions are to penetrate quickly into the granular surface and bind the material together, to partially waterproof the granular surface to prevent water erosion, to provide a temporary riding surface prior to overlay or seal coating and to provide a bond between the existing surface and the new wearing surface.
The asphalt emulsions used as prime coats typically contain a combination of asphalt and specially engineered agents to aid in penetrating the granular surface, while binding the aggregate particles to achieve stabilization.