Southeast South Dakota Union County Public Works Administrator, Raymond Roggow, has applied fog seal to all of his county’s chip-sealed roads for most of the past five years and is very pleased with the results. This practice has allowed highway officials to extend the life of chip-sealed road surfaces for at least one year, he says, which significantly reduces highway maintenance costs.

“We have no more windshield calls since we started fog sealing,” Roggow says. “That’s been a very positive outcome of the practice. Before we used the fog seal, we were striping our roads every year. Now the striping is lasting two years or more before it has to be redone. That’s significantly reducing our maintenance budget.”

Roggow also appreciates the contrast between the dark surface of a fog sealed road and the striping. He says the benefits of fog sealing haven’t gone unnoticed by drivers in the county.

“When you apply fog seal, the road looks like it’s been overlaid with asphalt,” Roggow says. “People like the finished appearance of the road. They also appreciate the visibility of the striping at night. It makes nighttime travel much safer. With the dark road surface, you also have an advantage in winter. Ice and snow will melt somewhat faster because the road surface heats up more quickly on a sunny day.”

Fog sealing is an application of asphalt emulsion sprayed onto a pavement surface with or without a sand cover. The emulsion is diluted to the proper consistency to obtain complete coverage of the roadway. Because fog seal works better on a coarse aggregate surface where asphalt emulsion has room to bond between aggregate particles, fog sealing is a highly satisfactory complement to a chip seal surface.

If fog seal is applied to a smooth aggregate surface, a dry choke cover is applied to prevent a slippery road surface. The choke is generally sand or aggregate less than 0.25 inches in diameter.

Fog seals are used to delay weathering of pavement, to waterproof the pavement surface, to improve the pavement’s ability to keep water from penetrating the base course or subgrade, and to reduce raveling.

The necessities

Equipment required to apply fog seal is a distributor truck used to dispense the asphalt emulsion. If sand is applied, a sand spreader is also required. Fog sealing a chip sealed road requires brooming excess chips with a power broom prior to application.

Roggow notes that Union County didn’t need to purchase any additional equipment to implement the fog seal.

“We use a Roscoe 2,500-gallon unit that sits on the bed of an older Ford truck,” Roggow says. “When we started using fog seal in 2005, we did some test sections. We were pleased with those first results and started using fog seal to follow up all our chip seal work.”

Jebro, Inc. in Sioux City, IA, provides the non-polymer emulsion for Union County. The product is a CSS-1 and CSS-1H type and grade with application temperatures between 100 and 170 degrees.

Recommended application rate is 0.10 to 0.15 gallons per square yard; a 1:1 dilution. Jebro Inc. Account Manager Mike Spohr says fog sealing has gained popularity in recent years primarily because it helps reduce costs.

“Everyone likes the fact that it helps hold aggregate in place once a road is chip sealed,” Spohr says. “It’s easy to apply. One of the challenges to using it is making sure weather conditions are just right so it sets within a couple of hours.”

The challenges

Sunny, warm and dry are the conditions best suited for fog sealing. A breeze will help set the emulsion that much faster. Roggow says his crew generally selects a 10- to 15-mile stretch of road that was recently chip sealed and contacts residents along the road so they can plan to restrict travel while the emulsion is being applied.