A fog seal applies a light, mist-like layer of fog-seal material onto an asphalt pavement using specialized high-pressure spraying equipment, forming a thin protective film. Depending on whether fine aggregate such as silicon carbide, quartz sand or basalt sand is added, it is divided into non-sand fog seal and sand fog seal (sand fog seal is required on expressways and first-class highways).
Fog seal is used on pavements showing light raveling, minor bleeding/texture loss, water seepage and asphalt aging. It suits roads of all classes but is best for medium- and light-traffic roads, and requires the existing pavement to still be in good condition.
Fog-seal material is chosen by pavement condition:
A dedicated fog-seal spray truck is required; small hand-held sprayers may be used for small areas. The spray bar height and nozzle angle must be set so that two or three nozzles overlap at every point, with no clogged nozzles and stable pressure.
Before work, calibrate the application rate:
A trial section of at least 200 m must be laid first, and the design rate adjusted to the surface density, roughness, seepage and raveling of the actual road.
| Check item | Frequency | Requirement |
|---|---|---|
| Appearance | Continuous | Uniform, no runs, bare spots, streaks, bleeding or oil patches; straight edges and joints |
| Water seepage coefficient | 5 points/km | ≤10 mL/min |
| Skid resistance (pendulum / texture depth) | 5 points/km | Meets design requirements |
Fog seal seals hairline cracks, blocks water infiltration, recharges aged binder, resists UV oxidation, leaves the road black and non-glare, and is a low-cost, fast preventive treatment that defers major resurfacing for 1–2 years.