What’s the Deal with Chip Seals?

By May 6, 2021Articles

Chip seal speed limit sign

Washtenaw County road users will soon see “Loose Stones – 35 mph” signs on various county roadways. These signs indicate that a road was recently chip sealed.

Chip sealing (aka seal coat) is an important strategy in WCRC’s efforts to maintain our 1,652-mile road network. When applied at the right time, a chip seal treatment can extend the lifespan of a road and help keep potholes at bay. This summer, we will chip seal approximately 100 miles of roadway.

But for a few exceptions, we will now fog seal roads after they have been chip sealed. A fog seal is another thin layer of liquid asphalt that is applied once

WCRC will apply a fog seal to chip sealed roads this season. Fog seal helps lock in the chips.

the excess chips have been swept up. This additional treatment helps to seal in the stones and extend the life of a chip seal. WCRC crews will return to fog seal within a couple of weeks after a road has been chip sealed, depending on the weather. Once the fog seal has been applied the road will be temporarily closed, vehicles will be prohibited from driving on it for a couple of hours as it cures.

Chip seals prevent potholes and help roads last longer.

Similar to how one might seal their driveway or patio deck, WCRC applies chip seals to paved roads that are in good to fair condition to extend their lifespan and protect the road from the wear and tear of vehicles, sun damage, and Michigan’s freeze/thaw cycles which produce cracks and lead to potholes. A typical chip seal treatment will extend the service life of a road by 3 to 5 years.

Chip seals are low-cost and allow WCRC to maintain more miles of road annually.

Chip sealing costs a fraction of the price to rebuild a deteriorated road. A chip seal costs approximately $23,000 per mile, compared to approximately $350,000 per mile to pulverize and repave a road in poor condition.

While chip sealing allows WCRC to maintain more miles of road at a lower cost, it is important to note that chip seals are only a surface treatment. A chip seal will not fill potholes or fix existing bumps in the road. For this reason, it is important to apply a chip seal before the deterioration happens.

How does a chip seal application work?Chip seal operation - chip spreader

A thin film of heated liquid asphalt is sprayed onto the road surface, followed immediately by the placement of small aggregate/stones (“chips”). The chips are then embedded into the liquid asphalt with rollers. Traffic can travel on the road approximately 15 minutes after the chip seal treatment is applied, but it is important that motorists do not exceed 35 mph!

Once the chip seal application has been completed, the excess stone will be swept off the road surface and within a couple of weeks, WCRC crews will return to apply the fog seal which can take up to a couple of hours to cure.

Once the road has been fog sealed, WCRC’s contractors will apply the permanent pavement markings.

 Will this process damage my car?

Chip sealed roads are safe to drive on, but it is important motorists do not exceed 35 mph. Driving 35 mph or less will prevent loose stones from kicking up. While a freshly chip sealed road appears coarse, the stones will further compact into the road surface over time.  Application of the fog seal and further embedding of the stones under traffic will result in a smoother road surface.

The liquid used for the fog seal may take up to a couple of hours to cure after application. It is very important for vehicles to stay off the road during this time to prevent damage to the road and vehicles.

To learn more about WCRC’s 2021 construction projects, visit: www.wcroads.org/road-work-construction/projects/