Fog Seal

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A single light application of emulsified asphalt is sprayed on an existing asphalt surface. A slow-setting and low-viscosity grade of emulsified asphalt is commonly used to allow the emulsion flow easily into cracks and surface voids. This also enables the emulsion to coat aggregate particles on the surface and further improves the waterproofing of the surface.


Equipment Variations

A properly calibrated emulsion distributor can be used for spraying emulsions. Calibrated emulsion distributors are preferred when the site allows.

ASTM D-2995 can be used to estimate emulsion application rate and residual application rate.

Material Variations

Slow-setting types of emulsion are normally used in order to properly seal small cracks. These emulsions are often diluted with water prior to application to reduce viscosity for spraying. Dilution is performed in varying proportions - up to 1 part emulsion to 5 parts water, but in most cases, a one-to-one dilution is used.

Types of emulsion used for a fog seal application are SS-1, SS-1h, CSS-1, or CSS-1h. Some agencies may accept the use of rapid-setting emulsions (i.e RS-1 or CRS-1), however, these types of emulsions cannot be diluted with water and may require specific emulsifier solutions to produce stable dilutions. 


  • Dilution may be improved by pre-warming the dilution liquid to 25 to 90° C (77 to 194° F).
  • Never add emulsion to water, always add water or other diluent to emulsion.
  • Diluted emulsions are normally not stored, unless bad weather necessitates temporary storage.
  • Water for dilution should be clean, potable water, free from detectable solids or incompatible soluble salts.
  • Test for dilution incompatibility, whenever in doubt, by diluting the emulsion in the severest conditions anticipated (e.g., high dilution, cold water, hard water, high shear pumps). 

Common Combinations

  • Fog seals can be combined with chip seal applications to hold chips in place and prevent vehicle damage arising from flying chips.
  • Fog seals can be combined with FDR and CIR applications to hold surface fines in place and prevent raveling from early traffic application.