Asphalt Emulsion: What It Is, Grades, and Where It's Used

Asphalt emulsion is liquid asphalt broken into tiny droplets and suspended in water with the help of an emulsifying agent, a bit like how soap lets oil mix with water. Asphalt on its own is too thick to spray or spread unless it's heated to high temperatures. As an emulsion, it flows at much lower temperatures, can be pumped and sprayed, and turns back into a sticky asphalt film once the water leaves. It's the base for tack coats, fog seals, chip seals, slurry seals, some cold mixes, and many driveway sealers.

What asphalt is made of → Driveway sealer calculator →

What's in an Emulsion

• Asphalt binder: commonly the majority of the product by weight, often somewhere around 55 to 70 percent depending on the grade.
• Water: most of the rest.
• Emulsifier: a small amount of surfactant chemistry that gives droplets an electrical charge and keeps them from clumping.
• Modifiers: some grades add polymers or latex to improve flexibility and chip retention.

"Breaking" and Curing

An emulsion is designed to be temporary. Once applied, the droplets need to come back together. That process is called breaking. You can see it: the emulsion goes on brown and turns black as it breaks. Then it cures as the remaining water evaporates and the asphalt film gains strength.

What speeds breaking: warm temperatures, sun, wind, low humidity, and contact with aggregate that reacts with the emulsifier. What slows it: cool, damp, still air. That's why emulsion work, including DIY driveway sealing, is weather sensitive, and why rain on a fresh coat can wash it away.

Anionic vs. Cationic

Emulsifiers give droplets either a negative charge (anionic) or a positive charge (cationic). Many aggregates carry a surface charge too, so pairing the right emulsion with the stone improves how well it sticks and how quickly it breaks. In grade names, a leading "C" usually means cationic, and no letter means anionic.

Reading Grade Names

Road emulsion grades follow a pattern. The exact specs come from standards bodies and state agencies, but the letters tell you a lot:

Code	Meaning	Common uses
RS / CRS	Rapid setting	Chip seals, where stone must stick fast
MS / CMS	Medium setting	Mixing with open-graded aggregate
SS / CSS	Slow setting	Tack coat, fog seal, slurry, dense mixing
QS / CQS	Quick setting	Slurry seal and micro-surfacing
h (suffix)	Harder base asphalt	Often seen in tack and fog grades
P or L (suffix)	Polymer or latex modified	Better chip retention and flexibility

So a CRS-2 is a cationic, rapid-setting grade, and an SS-1h is an anionic, slow-setting grade with a harder asphalt.

Where Asphalt Emulsion Is Used

• Tack coat: the bonding layer between old and new asphalt. See tack coat.
• Fog seal: a light diluted spray that refreshes aging pavement. See fog seal.
• Chip seal: binder for stone chips on roads and rural drives. See chip seal driveway.
• Slurry seal and micro-surfacing: thin mixtures of emulsion, fine aggregate, and additives spread over roads.
• Cold mix and stockpile patch: some patch products use emulsions; others use cutback asphalt with solvents.
• Driveway sealcoat: asphalt emulsion is the base of many retail and commercial sealers, blended with clay, fillers, and sometimes sand or polymers.

Asphalt Emulsion Sealer vs. Other Sealers

For driveways, "asphalt emulsion sealer" usually means a water-based sealer with asphalt as the binder. The main alternatives are refined coal tar sealers and acrylic or other polymer sealers. Coal tar sealers are restricted or banned in some states and localities, so emulsion sealers are the common choice in many areas. Our guides on oil-based vs water-based sealer and acrylic sealer compare them.

Handling and Storage

• Don't let it freeze. Freezing can break an emulsion in the container, ruining it. If a pail froze, see driveway sealer froze.
• Stir, don't shake hard. Retail sealers settle; follow the label for mixing.
• Clean tools with water while the product is still wet. Once broken, it takes solvent or scraping.
• Watch the weather. Labels list minimum temperatures and dry-time needs. Follow them.

Emulsion vs. Hot Asphalt vs. Cutback

• Hot asphalt binder is heated until it flows, used in plant-made hot mix and some chip seals and tack coats.
• Cutback asphalt is binder thinned with petroleum solvents. It releases those solvents as it cures, and its use is restricted in many areas for air-quality reasons.
• Emulsion uses water as the carrier, so it works at lower temperatures without solvent release.

Bottom Line on Asphalt Emulsion

Asphalt emulsion is asphalt made sprayable by suspending it in water. It goes on brown, breaks to black, and cures as the water leaves. Grade names tell you its charge and setting speed, and it's the working liquid behind tack coats, fog seals, chip seals, and many driveway sealers. Keep it from freezing and apply it in warm, dry weather.