Fog Coat to be Applied to Chip Sealed Roads

I am not sure this is good news or bad. I am definitely going to avoid these roads for a while.

Fog coat to be applied to chip sealed roads

Boulder County, Colo. – Beginning this Tuesday, Sept. 7, the Boulder County Transportation Department will apply a fog coat to three roads that were recently chip sealed. Fog coat is a petroleum-based material that helps level the surface of a chip-sealed roadway, providing a smoother ride for motorists and cyclists.

Fog coat schedule:
• Sept. 7-8: Nelson Road from U.S. 36 to 75th Street
• Sept. 8-9: Olde Stage Road from Lee Hill Drive to Lefthand Canyon
• Sept. 9-10: Cherryvale Road from Baseline Road to State Highway 170

To minimize traffic delays, the fog coat applications will take place between 8 p.m. and 5 a.m. Message boards are in place to provide advance warning and flagging crews will manage traffic at each location. Schedules are subject to change due to weather and other factors. Visit for updates.

All three roads are part of popular cycling routes. To mitigate effects on cyclists and improve ride-ability on these roads, Boulder County has made significant changes to its chip seal methodology. The county switched from a 3/8-inch chip to a 1/4-inch chip and is fog coating each chip-sealed road. The smaller chip combined with the application of the fog coat better fills spaces and provides a smoother finish.

“The new surface will not ride like pavement, but we are hopeful this new process will provide a better ride quality – particularly for cyclists – and still extend the life of our pavement investment,” Boulder County Transportation Director George Gerstle said. “We have been getting positive feedback from bicyclists on the new chip technique, and I believe the fog coat will provide additional improvement.”

Chip seal is a cost-effective preventative maintenance strategy for extending the life of pavement. It can add up to 10 years to the life of asphalt pavement, saving thousands of dollars in maintenance and rehabilitation costs. It is important to seal the entire road surface, including shoulders, to gain the maximum effectiveness from the procedure.

Another method of gaining maximum effectiveness from chip sealing is to perform the work before roads are in poor condition, generally within 5-7 years of a road being newly paved or overlaid. This is why the procedure is often applied to roads that appear to be in good condition.

Dan Rowland, Communications Specialist
Boulder County Commissioners’ Office

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What is a Fog Coat...

aka ...Fog Seal
A fog seal is an application of asphalt emulsion sprayed onto a pavement surface with or without a sand cover (figure 3). The emulsion is diluted to the proper consistency in order to get complete coverage on the roadway but not be too thick to cause a slippery surface. A fog seal works better on a coarse aggregate surface where the asphalt emulsion has room to pond between the aggregate particles. On a smooth aggregate surface, the asphalt rests on the surface covering the top of aggregate particles, creating a slippery surface for the vehicles. If the fog seal was not properly applied and a slippery surface exists, a dry choke cover is applied to the surface. The choke is usually clean sand or aggregate that is less than 0.25 inches in diameter.