Coal Tar vs. Asphalt Emulsion: Pros, Cons, and Why One Is Banned in Greenville County

When a property manager asks us what kind of sealer we use, the answer matters more than most people realize. Not because of brand preference or price — but because one of the two most common sealcoating base materials carries a serious environmental and health risk that has led municipalities across the country, including Greenville County, to restrict or outright ban its use on commercial properties.

That material is refined coal tar sealer (RTS). And if a contractor shows up to your lot with it, that's your cue to ask harder questions.

Here's what the chemistry actually tells us.

What Is Sealcoating, and Why Does the Base Material Matter?

Sealcoating is a colloidal suspension — solid bituminous particles suspended in water using clay emulsifiers (typically bentonite or ball clay). When applied correctly and allowed to cure, it forms a protective film over the asphalt surface that shields against UV oxidation, water infiltration, and petroleum-based chemical damage.

The base material is the sealer concentrate before water, sand, and polymer additives are blended in. It determines the chemical properties of the finished product — how it bonds to asphalt, how it resists fuel spills, and critically, what it leaves behind when rainwater washes off the surface and into storm drains.

There are three primary base materials used commercially:

• Refined Coal Tar (RTS) — derived from the byproduct of coal processing
• Asphalt Emulsion (AE) — derived from the same petroleum base as the asphalt itself
• Petroleum Resin (HP) — a newer category with premium performance characteristics

For commercial parking lots in the Greenville-Spartanburg area, the decision is almost always between RTS and AE.

The Performance Comparison: Where Coal Tar Actually Wins

To be straight about it: coal tar does perform better in certain measurable categories. This is part of why it dominated the industry for decades and why some contractors still push it.

Coal tar sealer's superior oil resistance comes from its chemistry. Polycyclic aromatic hydrocarbons (PAHs) — the same compounds that make it an environmental hazard — are also what make it chemically resistant to petroleum spills. Gasoline and motor oil are essentially unable to dissolve a coal tar sealer film.

Asphalt emulsion sealer, being derived from the same petroleum family as gasoline and oil, has moderate resistance at best. A high-traffic automotive service area that gets regular oil spills will degrade AE sealer faster than coal tar.

So Why Is Coal Tar Banned in Greenville County?

The same PAHs responsible for coal tar's performance are classified as probable human carcinogens by the EPA. The USGS has documented that coal tar pavement sealant is one of the largest sources of PAH contamination in urban waterways — concentrations in storm runoff from sealed parking lots can run 65 times higher than runoff from unsealed lots.

When it rains, microscopic particles of cured sealer become airborne, wash into storm drains, and accumulate in sediment. Children playing near treated lots track it inside on their shoes. Workers applying it face direct dermal exposure and inhalation risk.

Greenville County's ordinance restricting coal tar pavement sealants is part of a national trend that includes bans in Austin, Washington D.C., the entire state of Washington, and dozens of municipalities across the country. The science driving these policies is consistent: coal tar sealer works well for the pavement, and it works poorly for everything else nearby.

For commercial property owners, this isn't just an environmental question — it's a liability question. Using a banned product on your property, or hiring a contractor who does, creates exposure that no facility manager wants to deal with.

What Asphalt Emulsion Gets Right

Modern asphalt emulsion sealer, properly formulated with polymer additives and UV stabilizers, has closed much of the performance gap with coal tar — on every metric that doesn't involve direct petroleum exposure.

UV Protection: The primary threat to asphalt is UV oxidation — the process by which sunlight converts flexible maltenes in the bitumen binder into brittle asphaltenes, turning your lot gray and crack-prone. AE sealer with quality UV-blocking additives creates an effective barrier against this. In the South Carolina climate, where pavement surface temperatures can reach 120°F on a 75°F day, UV shielding is the single most important protective function sealcoating provides.

Water Penetration: Both sealers perform comparably in blocking water infiltration, which is the second major threat to asphalt. A properly applied two-coat AE system fills surface pores and creates a waterproof barrier that protects the structural layers below.

Adhesion: Coal tar bonds chemically and penetratively into asphalt pores. Asphalt emulsion creates a mechanical bond — the sealer works into surface texture and locks in through physical contact. For a first coat on an aged, oxidized lot, the industry standard is to apply AE by squeegee, which forces the material into the pores under downward pressure before the spray coat goes on top.

Applicator and Customer Safety: AE sealer presents essentially no skin burn risk and produces minimal odor compared to coal tar, which carries both a thermal burn risk during application and a persistent chemical odor.

The Two-Coat Standard and the 50/50/50 Rule

Regardless of sealer type, application method matters as much as chemistry. The industry standard for commercial lots is always a two-coat system — never a single thick coat.

Here's why: a thick single coat (above 20 mils wet film thickness) will skin over on the surface while the interior remains wet, trapping water underneath. The result is mud-cracking and pin-holing — the sealer literally bubbles and fractures from within as the trapped moisture tries to escape.

Two thin coats, applied sequentially after the first has cured to traffic, produce a stronger, more durable finish than one heavy application. This is physics, not opinion.

Environmental conditions at application time are equally non-negotiable:

In the Greenville-Spartanburg summer, pavement temperature is the most commonly violated condition. Black asphalt absorbs roughly 90% of solar radiation. On a standard summer day, pavement surface temperature frequently exceeds the 140°F maximum by mid-morning. Contractors who don't measure surface temperature with an infrared thermometer before each pass are guessing — and when they guess wrong, the property owner pays for it.

What This Means for Your Property

If you manage commercial property in Greenville County, the decision between coal tar and asphalt emulsion has already been made for you by ordinance. But the more important decision is making sure the contractor you hire:

1. Uses a properly formulated asphalt emulsion sealer with UV stabilizers and polymer additives
2. Applies a two-coat system — not a single thick coat to save time
3. Verifies the 50/50/50 conditions before starting, including pavement temperature measurement
4. Preps oil spots with an oil spot primer before sealing (sealer will not bond to petroleum-saturated asphalt)
5. Maintains proper mechanical agitation in the spray tank throughout the job to prevent phase separation

At Strike Force Striping, we use asphalt emulsion exclusively — not because the county requires it, but because when you understand the chemistry, it's the correct choice for commercial applications in this climate. We carry infrared thermometers on every rig. We don't seal lots at 2 PM in August. And we document everything.