Fog Seals

A fog seal is a light application of a diluted slow-setting asphalt emulsion to the surface of an aged (oxidized) pavement surface. Fog seals are low-cost and are used to restore flexibility to an existing HMA pavement surface. They may be able to temporarily postpone the need for a surface treatment or non-structural overlay.

Figure 1: Maintenance patch on a longitudinal joint covered by a fog seal.

Figure 2: Parking lot showing no treatment on the left side and a fog seal on the right side.

Purpose

Preventive maintenance. Fog seals are used to restore or rejuvenate an HMA surface. They may be able to postpone the need for a BST or non-structural overlay for a year or two.

Materials

Slow-setting asphalt emulsion.

Mix Design

None beyond the manufacturer’s. A test patch may be needed to determine the proper application rate.

Other Info

Fog seals are suitable for low-volume roads which can be closed to traffic for the 4 to 6 hours it takes for the slow-setting asphalt emulsion to break and set.

An excessive application rate may result in a thin asphalt layer on top of the original HMA pavement. This layer can be very smooth and cause a loss of skid resistance. Sand should be kept in reserve to blot up areas of excess application.