Fog Seal Emulsion
A fog seal is a light application to an existing surface of a slow-setting asphalt emulsion diluted with water, similar to a tack coat. It can be diluted in varying proportions up to one part emulsion to five parts water, but in most cases a one to one dilution is used. Grades of asphalt emulsion normally used for this purpose are SS-1, SS-1h, CSS-1, or CSS-1h.
A fog seal can be a valuable maintenance aid when used for its intended purpose. It is neither a substitute for an asphalt surface treatment nor a seal coat. It is used to renew old asphalt surfaces that have become dry and brittle with age and to seal small cracks and surface voids. The fairly low viscosity diluted emulsion flows easily into the cracks and surface voids. It also coats aggregate particles on the surface. This corrective action will prolong pavement life and may delay the time when major maintenance or reconstruction is needed.
The total quantity of fog seal used is normally in the order of 0.45 to 0.70 liter/m² (0.1 to 0.15 gal/yd²) of diluted material. Exact quantities are determined by the surface texture, dryness, and degree of cracking of the pavement on which the fog seal is sprayed.
The same traffic restraints used with tack coats should be employed with fog seals.
Over-application must be avoided, as this would result in an asphalt pickup by vehicles and possibly a slippery surface. If an excess of emulsion is applied, a light dusting of the affected area with a fine sand may remedy the problem.