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Posted on: August 21, 2019

Fog sealing: What is it?

Fog sealed road

Hillcrest Drive in northeast Minot was chip sealed this summer using the fog sealing process, leaving the roadway with the look of asphalt.


Crews working to chip seal roads in Minot is a common sight every summer, this year included. But residents might notice a difference in the final appearance of some roads this year.

The chip sealing process used this year is the same process as in previous years, with one notable exception: A fog seal that leaves the road looking like asphalt instead of the typical rock-covered surface that residents have seen.

The typical chip sealing process looks like this:

  • Sweep the road
  • Lay down a layer of oil
  • Truck lays down rock chip layer within 60 seconds
  • Compactor immediately follows to push chips into the oil layer
  • Sweep up loose rocks
  • Allow traffic on the road for 24 hours
  • Sweep up any loose rocks again

This year, there’s one added step: A thin layer of oil is sprayed over the road as a final coating to seal in any loose rocks.

“We’ve had multiple areas that required warranty work in the past few years, so this fog seal process is something that we can do to help the contractor ensure the City gets a better end product,” said Jesse Berg, a project manager with the City of Minot’s engineering department. “The extra layer helps lock in any loose chips. We want that fog seal to find any low spots and fill in the voids between the chips.”

A section of 16th Street Northwest was chip sealed using the traditional method in 2018, and experienced significant chip loss. Berg said the contractor is required to redo the project in 2020, at no additional cost to the City.

Berg said the oil used for the fog seal is different than the oil used earlier in the chip seal process. It’s thinner, it sets up and cures a little slower, and is applied at a rate of .1 gallons per square yard, compared to .4 gallons per square yard for the initial oil layer.

The process requires additional time to allow the fog seal to cure, Berg said, which means more traffic control measures are required.

“In the past we’ve tried to shy away from using this process in town, because you have to keep traffic off the road for a longer period of time, maybe up to two hours,” he said. “But this year we had good weather and we were able to reopen roads that had been fog sealed in an hour or less after they had been completely fogged.”

Data from the North Dakota Department of Transportation and other entities shows a better end result with fog sealing, and recommends chip seal projects be completed before Sept. 1. Berg said chip sealing projects in the city will be finished by Aug. 30.

“We’ve made sure our schedule adheres to that recommended Sept. 1 deadline. Temperature plays a role in that, and being done earlier allows the road to have more traffic on it before winter and that helps cure the oil and push the chips further down into the oil,” Berg said. “The results are better if we get done earlier.”

Fog sealing has been used in Minot on asphalt fitness trails and walking paths, but this is the first year it’s been used on street projects. The Department of Transportation uses the process, as does Ward County.

“Our end product will be better because of this application, and that adds to the longevity of our roads,” Berg said. “It doesn’t add a lot to the cost of a project, and all the data has shown that it absolutely helps with chip retention.”

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