Coal Tar vs Asphalt Emulsion Sealer: What Belongs on Your Rochester Driveway

Walk up to a Rochester sealcoating crew and ask what's in the tank. About half the time you'll get a straight answer. The other half, you'll hear "premium commercial-grade sealer" — which tells you nothing about what you're actually paying to have applied to your driveway for the next two or three years.

The two products doing the real work in the Rochester market are coal-tar emulsion and asphalt emulsion. They look nearly identical going down. They both dry to a flat black finish. They both check the "sealcoating" box on a quote. But they are not the same thing, they don't perform the same way, and the regulatory picture around one of them is shifting in ways that should affect your decision. Here's what actually separates them.

What coal-tar sealer is and why the industry defaulted to it

Coal-tar emulsion — sold under designations like RT-12 or refined tar sealer — is derived from the byproduct of steel production, specifically from the distillation of coal. It has been the dominant commercial pavement sealer in the United States for most of the last 60 years, and for defensible reasons: it outperforms asphalt emulsion on durability, resists oil and petroleum penetration almost completely, and holds up better under heavy vehicle traffic.

That petroleum resistance is why you see coal tar on gas-station aprons, commercial parking lots, and industrial facilities. When a fuel spill hits an asphalt-emulsion-sealed surface, the oil can attack and soften the sealer over time. On coal-tar-sealed asphalt, the same spill beads up and wipes off. The chemistry is fundamentally different: coal tar contains aromatic compounds that are chemically inert toward petroleum distillates, where asphalt emulsion shares a molecular relationship with the fuels it's trying to repel.

For a high-traffic commercial lot, that resistance matters. For a residential driveway where the biggest petroleum hazard is a slow drip from a parked car, it matters a lot less.

What the EPA found, and what happened after

This is where coal tar gets complicated. The Environmental Protection Agency, alongside studies conducted by the U.S. Geological Survey, identified coal-tar sealer as a significant source of polycyclic aromatic hydrocarbons — PAHs — in urban stormwater runoff. Coal-tar-sealed pavement surfaces shed PAH particles at concentrations that are orders of magnitude higher than asphalt-emulsion-sealed surfaces, and those particles wash into storm drains, collect in adjacent soil, and eventually reach waterways.

PAHs are classified by the EPA as probable human carcinogens. The USGS work, published across multiple studies between 2005 and 2015, found PAH concentrations in sediment near coal-tar-sealed parking lots running 65 times higher than near unsealed or asphalt-emulsion-sealed lots.

The regulatory response has been uneven. Washington DC, Minnesota, and Washington state have banned coal-tar pavement sealers outright. Several municipalities in those and other states have local bans. Parts of New York state have begun restricting use. The Rochester area does not currently have a blanket municipal ban, but the regulatory trajectory is worth watching — a contractor who is honest with you will tell you the status in your specific municipality before they apply anything.

Asphalt emulsion: the chemistry

Asphalt-emulsion sealer is made from the same base material as your pavement — petroleum-derived asphalt, suspended in water with emulsifying agents. It's water-based, lower-VOC, and lower-odor than coal tar. It cures through water evaporation rather than chemical curing, which is why the 24-hour no-rain window matters as much for asphalt emulsion as for coal tar.

The tradeoffs are real. Asphalt emulsion is less resistant to oil and fuel penetration than coal tar. It typically requires reapplication on a slightly shorter cycle in high-traffic conditions. It doesn't achieve the same depth of black color that fresh coal tar shows — asphalt emulsion tends toward a slightly softer, browner black after the first season of UV exposure. In side-by-side conditions, most Rochester homeowners see asphalt emulsion lasting 24 to 30 months before it starts to visibly fade and thin, versus 30 to 36 months for a well-applied coal-tar coat.

What asphalt emulsion does not have is the PAH issue. It is the product preferred by the Pavement Coatings Technology Council for residential applications and is the default choice for contractors operating in or near environmentally sensitive watersheds — which, in Monroe County, includes a fair amount of the residential stock near Irondequoit Creek, Oatka Creek, and the fingers of the Genesee drainage basin.

What gilsonite-modified sealers are (and why some contractors push them)

A third category has entered the Rochester market: gilsonite-modified asphalt emulsion, sometimes marketed as "polymer-modified" or "fortified asphalt" sealer. Gilsonite is a naturally occurring solid hydrocarbon — technically a type of asphaltite — that's mined primarily in Utah. Adding it to asphalt emulsion increases hardness, UV resistance, and petroleum resistance without the PAH profile of coal tar.

Gilsonite-modified products sit in the middle of the performance spectrum. They outperform straight asphalt emulsion on durability and petroleum resistance, approach but don't match coal tar on petroleum-spill resistance, and carry none of coal tar's regulatory baggage. The catch is cost: gilsonite-modified sealer runs roughly 20 to 30 percent more per gallon than commodity asphalt emulsion, and not every Rochester contractor stocks it.

The visual difference after 18 months of UV is actually noticeable in side-by-side conditions. Straight asphalt emulsion grays and softens in the second year; gilsonite-modified products hold their depth noticeably longer. For homeowners who want the longevity argument for asphalt-emulsion-class chemistry, gilsonite-modified is worth asking about.

What the right answer looks like for a Rochester residential driveway

For a standard Rochester residential driveway — two cars, normal daily traffic, no history of major fuel spills — asphalt emulsion is the correct default. It performs adequately in freeze-thaw conditions, it avoids the PAH issue, and it's the product that will continue to be available without regulatory interruption as municipalities tighten coal-tar access.

The case for coal tar strengthens in specific conditions: heavy commercial traffic, a lot with a history of vehicle fluid contamination, or a surface that specifically needs the petroleum resistance advantage. In those cases, coal tar is still legal in Monroe County and still the more durable product.

The case against both commodity products is strongest if you're doing a two-coat job on a surface you want to protect for the full 30-month cycle without reapplication. In that case, asking your contractor about gilsonite-modified emulsion is a reasonable conversation.

What to actually ask your contractor:

• Which product are you using, and can you show me the spec sheet or MSDS?
• Is this product permitted in my municipality?
• What's the sand-additive rate? (Proper mix design calls for 2 to 2.5 lbs of silica sand per gallon of sealer — a skip on sand is a red flag regardless of product type.)
• If asphalt emulsion, is it straight or polymer-modified?

A contractor who can't answer the first two questions specifically shouldn't be applying anything to your driveway.

The one thing both products have in common

Neither coal tar nor asphalt emulsion will perform as advertised if the prep work is wrong. An oil spot that wasn't primed before the topcoat will bleed through both products within weeks. A crack that wasn't filled before sealing will reappear under both products inside one Rochester winter — water gets in, freezes, expands at roughly 9 percent, and opens the crack wider than it was before you paid someone to seal it.

The chemistry choice matters. It matters less than how well someone cleaned, primed, filled, and cut-edged your driveway before a single bucket of sealer went down.

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Ready to book a real two-coat seal for 2026 — the kind where someone shows you the spec sheet before they start? Get a free quote from Rochester Sealcoat or browse verified local sealcoating contractors who can walk through the product question with you directly. We cover Irondequoit, Penfield, Webster, and across Monroe County.

See also: our driveway sealcoating service overview and commercial lot sealcoating for parking surfaces where the product choice carries more weight.