New rejuvenators and polymer-modified emulsions are improving performance. At the same time, owners are using fog seals differently – earlier in the pavement life cycle, on repeat intervals, and as part of a broader preservation plan instead of a one-off treatment.
The result is a shift worth paying attention to. Fog seals are moving from a low-end maintenance option to a more deliberate tool for extending pavement life and smoothing out maintenance budgets.
The Outdated Perception
Use of fog seals, along with other asphalt surface sealing concepts, gained momentum after the oil crisis of the 1970s. Maintaining rather than replacing pavements became a priority as the cost of asphalt used in pavements soared.
Long viewed as a low-cost surface treatment for low-volume pavement, perceived fog seal product limitations have persisted over time even as formulations, applications and pavement preservation philosophies advanced.
The reputation comes, in part, from how fog sealing previously was applied – to structurally failed pavement (not an ideal candidate), under poor weather conditions (overcast or humid day with high moisture takes longer to cure) or without essential traffic control (necessary to keep traffic from driving through the application before it has time to cure).
Financial and industry culture issues may play a role in the perception problem as well. Fog sealing is inexpensive compared to overlays or mill-and-fill work, so it can be dismissed as low-tech or less important, favoring treatments that are more visible, capital-intensive or structurally oriented.
A philosophy shift, from fixing failed pavement cheaply to preserving newer pavement before deterioration accelerates, is gradually overcoming misconceptions about fog sealing performance today.
About Fog Sealing
Like sunscreen, fog sealing should be applied before too much pavement damage has occurred. In fact, to be cost-effective, it should be applied before most project decision makers typically consider its use.
It does not add structure or enhance a pavement’s load-bearing capacity as its function is to prevent the pavement surface from oxidizing – drying up and creating micro cracks which lead to bigger cracks, allowing more water to come into the pavement matrix and break down its components.
The initial black color of fog sealing can fade in as little as six months, but the protective layer of emulsion continues to do its job of keeping the surface moist over a much longer period of time.
At some point, the sun will win but reports from municipalities and state departments of transportation indicate that fog sealing can extend the life of pavement two to four years, depending on pavement condition and treatment timing.
Fog Sealing Evolves
As a nearly 100-year-old concept, fog sealing has gone through notable innovations in chemistry, application methods and functional design, evolving from tar sprays and diluted asphalt emulsion to trackless, high-performance and data-driven systems.
By the early 90s, fog sealing had progressed into slow-setting emulsions with applications moving to calibrated distributor-truck operations. The achievable goals became sealing surface voids, retaining aggregate, reducing raveling and improving waterproofing. Still, aspects of its shortcomings continued including inconsistent application rates, longer cure times, tracking onto vehicles and temporary loss of skid resistance.
Yet, as distributor truck calibration improved, agencies standardized application rates and dilution ratios became more controlled, fog sealing earned a role in preventative maintenance, the Federal Highway Administration (FHWA) reports.
Eventually that organization, and pavement preservation organizations, institutionalized fog sealing’s place in lifecycle asset management, recognizing significant improvements:
- Application – calibrated distributor trucks, more strict weather condition requirements, traffic-control standards, friction management practices and use of blotter sand when needed
- Material – improved emulsion chemistry, better curing outcomes, compatibility with chip seals and open-graded friction courses
- Focus – shoulders, oxidized and raveling-prone surfaces
A Chemistry-Driven Preservation Treatment
In the continuum of pavement preservation, rehabilitation and reconstruction, fog sealing lands squarely in the preservation category.
No longer thought of as just a surface-sealing solution, developments in the last 10-15 years have revolutionized fog sealing as an engineered pavement-preservation system focused on oxidation control, binder chemistry restoration and lifecycle extension.
Today, users recognize the difference between conventional and rejuvenating fog seals that are designed to penetrate oxidized binder, restore viscoelastic properties, slow oxidation, improve flexibility and reduce brittle cracking.
While rejuvenating fog seals still use asphalt emulsion technology, they also have agents designed to penetrate aged asphalt binder and restore flexibility and often include polymer modification to improve durability, adhesion and traffic performance, especially on higher-volume roads.
With improvements in formulation came higher standards in application discipline with tighter guidelines on nozzle configuration, distributor calibration, pavement temperature, curing conditions and traffic reopening.
The most recent innovations in fog sealing have led to faster-curing, trackless formulations and friction-conscious designs with standard application methods now using GPS-guided distributor calibration, precise spray bars, lane-by-lane traffic staging and friction monitoring.
Meeting Asset Management And Environmental, Social And Governance (ESG) Goals
Some fog seal attributes have not changed since the early days – it can be applied quickly as a lower cost preventative maintenance technique. Coupled with all its modern innovations, this application meets several core asset management objectives:
- extending pavement service life
- delaying overlays and reconstruction
- improving lifecycle cost efficiency
- smoothing long-term capital spending
- preserving pavement condition indexes
- reducing deferred maintenance backlogs
For ESG initiatives, compared to reconstruction fog sealing has a relatively small material and carbon footprint because it works with the existing pavement structure instead of replacing it. This requires less asphalt binder, fuel, virgin aggregate, trucking, construction equipment and demolition.
Applied correctly and at the right pavement condition, fog sealing can help delay more expensive overlays and rehabilitation. Applied too heavily or after major distress develops and it can reinforce the old industry complaints about slickness, tracking and short-lived performance
