Fog seals are a method of adding asphalt to an existing pavement surface to improve sealing or waterproofing, prevent further stone loss by holding aggregate in place, or simply improve the surface appearance. (See above before (L) and after (R). To achieve this, the fog seal material (emulsion) must fill the voids in the surface of the pavement. This is accomplished in two steps. First, prior to application the surface must be thoroughly cleaned, using any combination of a blower, sweeper truck, and/or water truck. Second, during its application it must have sufficiently low viscosity so as to not break before it penetrates the surface voids of the pavement. This is accomplished by using a slow setting emulsion that is diluted with water.
Fog seals should only be used where surface penetration of the emulsion can be expected; that is, aged and raveled hot mix surfaces, chip-sealed surfaces, and open graded asphalt surfaces. On shoulders, gores, or dikes, penetration is desirable, but it is not essential. Fog seals darken the pavement surface and create distinct demarcation in these regions.