Coal Tar vs Asphalt Emulsion Sealer: Which Should You Use?

Coal tar and asphalt emulsion are the two black liquids that have dominated driveway and parking lot sealcoating for decades. They look almost identical in the bucket and on the pavement, both are usually mixed with water, and both are applied the same way. The difference is the binder: one is made from a by-product of turning coal into coke for steelmaking, the other from refined petroleum asphalt. That single ingredient decides how well the coating shrugs off spilled gasoline, how long it lasts, how unpleasant it is to apply, and whether it is legal to put down where you live.

For a home driveway, the answer is asphalt emulsion (or an acrylic or polymer sealer) in almost every case. Coal tar is genuinely tougher against fuel and sunlight, but its polycyclic aromatic hydrocarbon (PAH) content is far higher, it is banned in a growing list of places, and its advantages matter much more on a commercial lot with dripping delivery trucks than on a two-car drive.

A quick note on terminology, because it causes most of the confusion online. "Coal tar vs asphalt" is a question about the binder — the material left on the pavement after the sealer dries. "Oil-based vs water-based" is a question about the carrier — the liquid that evaporates. Most coal tar sealers sold today are water-based emulsions, exactly like most asphalt sealers. If your real question is about solvent-borne penetrating sealers versus water-based film formers, our guide to oil-based vs water-based driveway sealer covers that separately. This page sticks to the binder.

What Each Sealer Actually Is

Coal Tar Sealer

Coal tar is a thick black liquid driven off when coal is heated in coke ovens to make coke for steel production. Distilling it leaves coal tar pitch, and that pitch, emulsified in water with clay, surfactants and usually some filler and polymer, is the base of coal tar sealcoat. In the trade it is often called refined tar emulsion or RTS (refined tar sealer). Industry and USGS descriptions put the pitch content of a typical product at roughly a third of the wet material.

Chemically, coal tar is dominated by aromatic ring compounds rather than the long-chain hydrocarbons that make up petroleum. That is the source of both its strength and its problem. Aromatic structures are not dissolved by gasoline or motor oil, and they hold up well under ultraviolet light, which is why coal tar became the professional sealcoating standard for parking lots, gas stations and drive-throughs. The same aromatic chemistry is what makes it so rich in PAHs.

Asphalt Emulsion Sealer

Asphalt emulsion sealer uses refined petroleum asphalt — essentially the same family of material that binds the stones in your driveway — broken into tiny droplets and suspended in water with clay and emulsifiers. When it is spread, the water evaporates, the droplets coalesce into a continuous black film, and any sand or filler stays locked in that film. Budget products are mostly asphalt, clay and water. Better ones add latex or other polymers, which make the film tougher, more flexible and slower to fade.

Because the binder is chemically similar to the pavement underneath, asphalt emulsion bonds well and flexes with the surface through freeze–thaw cycles. Because it is petroleum-based, it is also vulnerable to the petroleum products that cars drip: gasoline and oil soften and dissolve it. That one trade-off — compatibility and lower toxicity on one side, chemical resistance on the other — is most of this comparison.

Side-by-Side Comparison

Figures are typical ranges from manufacturer literature and trade guidance for water-based emulsions of each type. Individual product labels override them.

Fuel, Oil and UV Resistance: Coal Tar's Real Advantage

It is worth being straight about this, because a lot of material on the subject treats coal tar as simply obsolete. It is not obsolete on performance. It became the professional standard for good reasons.

Fuel and oil. Asphalt is a petroleum product, so petroleum dissolves it. A gasoline spill on bare asphalt pavement or on an asphalt emulsion sealer softens the binder and leaves a dull, tacky spot that can eventually ravel. A car that leaks oil in the same place every night will slowly eat through an asphalt sealer coat. Coal tar's aromatic binder is not soluble in gasoline or motor oil in the same way, so a coal tar coat acts as a barrier that protects the pavement beneath it. At a filling station, a fast-food drive-through or a fleet parking lot, that difference is large and very visible.

Sunlight. UV breaks down asphalt binder and drives the oxidation that turns a black driveway grey. Coal tar weathers more slowly, holds its colour longer and keeps protecting the surface for longer between coats. Asphalt emulsion's colour loss is partly cosmetic — a faded coat is still doing some work — but it is the most common reason homeowners reseal.

How much this matters on a driveway. Less than it sounds. A typical home driveway sees two or three cars, little idling, occasional drips and the odd spill from a mower can. Those are handled perfectly well by an asphalt sealer plus two habits: wipe or absorb spills promptly, and treat oil spots with a dedicated primer before resealing (our guide to removing oil stains from a driveway covers this). If one car drips persistently, fixing the leak is a better answer than choosing a more toxic sealer.

Durability and Reseal Interval

Coal tar's track record is longevity. A properly applied two-coat coal tar job on a parking lot commonly runs three to five years before it needs redoing. A standard asphalt emulsion on a home driveway usually lasts two to three years, and the better polymer-modified asphalt products narrow the gap to three or four. Those ranges assume normal application rates; a thin coat of anything wears out faster.

Coal tar's weakness is flexibility. It is a harder, more brittle film, and it shrinks as it cures. Applied too thick, over too many existing layers, or on pavement that flexes, it develops fine surface cracking — often described as crazing or "map cracking" in the sealer itself. Contractors manage this with polymer additives and by keeping coats thin. Asphalt emulsion is more forgiving on residential pavement because it moves with the asphalt underneath through freeze–thaw cycles.

On a home driveway, a three-to-five-year interval versus a two-to-three-year one sounds like a big difference, but the real number is closer than that. Residential asphalt does not need sealing every year with any product, and most driveways should be resealed on condition — when water stops beading and the surface has gone grey — rather than on a fixed schedule. See how often to seal a driveway for the details. A polymer-modified asphalt emulsion applied at the right rate will often reach three or four years on a lightly used drive, which leaves coal tar's lifespan edge at about a year.

The PAH Problem

This is the reason coal tar sealer has gone from industry standard to banned product in much of the country, and it is worth understanding in proportion rather than through headlines.

What PAHs Are

Polycyclic aromatic hydrocarbons are a large family of compounds formed when organic material is burned or heated, so they are found in vehicle exhaust, wood smoke, grilled food and cigarette smoke. Several, including benzo[a]pyrene, are classified as probable or known human carcinogens, and many are toxic to aquatic life. Coal tar pitch itself is classified by the International Agency for Research on Cancer as a known human carcinogen. Asphalt contains PAHs too, but at far lower concentrations.

What USGS Research Found

Beginning in the mid-2000s, U.S. Geological Survey scientists published a series of studies on sealcoat. In summary, with the caveat that individual numbers vary by study, site and method:

• The products themselves: coal-tar-based sealcoat was reported to contain on the order of 1,000 times more PAHs than asphalt-based sealcoat.
• Pavement dust: dust swept from coal-tar-sealed parking lots carried PAH concentrations reported in the hundreds to roughly a thousand times higher than dust from unsealed lots or lots sealed with asphalt-based products.
• Homes: house dust in ground-floor apartments next to coal-tar-sealed lots was found to contain substantially higher PAH levels — around 25 times higher in one widely cited study — than in apartments next to lots without coal tar sealcoat.
• Waterways: worn sealcoat particles wash into storm drains, and USGS work linked coal tar sealcoat to a large share of the PAHs in sediment of many urban lakes and streams studied, with effects on aquatic organisms.

The mechanism is simple. Sealcoat wears. Tires and snowplows abrade it into fine particles, rain carries them into storm drains, wind lifts them, and shoes and pet paws carry them inside. Volatilisation also releases PAHs into the air above freshly sealed pavement, highest in the first days and weeks after application. Follow-on analyses estimated elevated lifetime cancer risk for people living next to coal-tar-sealed pavement, driven mostly by exposure in early childhood, when children spend time on floors and put their hands in their mouths.

Keeping It in Proportion

The industry has disputed parts of this research, particularly how much of the PAH load in sediment should be attributed to sealcoat rather than vehicle exhaust and other sources. But the core finding — that coal tar sealcoat contains vastly more PAHs than asphalt-based alternatives — is not seriously in question, and regulators in multiple states have acted on it. For a homeowner the decision does not require settling the debate. The alternatives cost about the same, are sold everywhere, and do the job on a driveway. There is little to gain from taking on the risk.

Bans and Restrictions

Austin, Texas, became the first city to ban coal tar sealant in 2006, after local studies tied it to PAHs in a creek. The District of Columbia followed. Washington became the first state to ban it, and Minnesota adopted a statewide ban as well. Since then additional states, and a long list of counties and municipalities — especially around the Great Lakes, in parts of the Northeast and in many Minnesota, Illinois, Michigan, Wisconsin and New York communities — have restricted or banned its sale, use or both.

The details differ from place to place. Some rules ban sale; some ban application; some apply only to certain PAH thresholds; some cover contractors and not homeowners, or the reverse. Lists maintained by advocacy groups and agencies are helpful but go out of date, so do not rely on any single list, including this page. Before you buy coal tar, use up leftover stock, or hire a contractor, check with your state environmental agency and your city or county public works or stormwater department.

Retailers moved too. The large home-improvement chains stopped stocking coal tar sealer for residential customers years ago, and in much of the country you would now have difficulty finding it on a shelf even where it remains legal. Where it is still used, it is mainly applied by commercial sealcoating contractors.

Odour, Skin Irritation and Cure

Odour

Fresh coal tar has a strong, sharp smell often compared to mothballs or creosote, and it lingers around the pavement for days in warm weather. Asphalt emulsion smells mildly of asphalt and dissipates quickly. If you have ever walked past a parking lot on the day it was sealed and noticed a penetrating chemical smell, that was very likely coal tar.

Skin and Eyes

Coal tar is a photosensitiser: compounds in it react with sunlight on the skin. Sealcoating crews have long reported burning, stinging skin and irritated eyes on sunny days, sometimes called "tar burn," that is distinctly worse than anything asphalt emulsion produces. That is one reason professional guidance for coal tar includes long sleeves, gloves, eye protection and sunscreen, and one reason many contractors were glad to move away from it. Asphalt emulsion is still a product you should keep off your skin — wear gloves and old clothes, and wash splashes off with soap and water while wet — but it does not carry coal tar's phototoxic effect.

Drying and Curing

Because both are water-based emulsions, they dry and cure in broadly similar ways. Both need the water to evaporate, so both depend heavily on temperature, sun, humidity and coat thickness. Typical guidance for each is foot traffic after 4–8 hours in good conditions and vehicles after 24–48 hours, with a minimum application temperature around 50°F and rising and no rain for at least a day. Some contractors find coal tar sets slightly faster in hot sun; the difference is small compared with the effect of weather. For realistic timelines by product and conditions, see how long driveway sealer takes to dry.

Cost and Availability

For a homeowner, cost is no longer much of a differentiator because coal tar is rarely on offer.

Historically, coal tar concentrate was cheap for contractors, because it is an industrial by-product, and its longer life lowered the cost per year on large lots. That advantage has eroded. The number of operating coke ovens in North America has fallen, supply has tightened, and the regulatory risk of holding coal tar stock has pushed many suppliers toward asphalt products. For a homeowner doing it yourself, a 500-square-foot driveway in two coats needs roughly 15–20 gallons of asphalt emulsion, which comes to about $60–$300 depending on grade. The full breakdown, including professional pricing, is in how much it costs to seal a driveway.

On a cost-per-year basis, a polymer-modified asphalt emulsion lasting three years compares reasonably with a coal tar coat lasting four, and that is before considering that you cannot easily buy the coal tar.

Switching From One to the Other

Many older driveways and most older parking lots have coal tar somewhere in their history, so this question comes up often. The good news is that, unlike switching between solvent-borne and water-based sealers, switching binders between two water-based emulsions is usually manageable. The rules below are general; the new product's label and the manufacturer's technical sheet take priority.

Asphalt Emulsion Over Old Coal Tar

This is the common direction now, and generally it works. Clean the surface thoroughly, let any recent coal tar coat weather (if it was applied within the last year or so, wait), fill cracks, and apply the asphalt emulsion as directed. Some manufacturers note that asphalt sealers over coal tar can show slight colour or sheen differences, and a few recommend a primer or a test patch on previously coal-tar-sealed surfaces. Do a small test area, let it cure, and press duct tape onto it; if the coat lifts with the tape, the surface needs more cleaning or a primer.

Coal Tar Over Asphalt Emulsion

Where coal tar is still legal and a contractor proposes it, it can generally go over a weathered asphalt-based coat once that coat is clean and sound. The concern is build-up: coal tar's shrinkage and brittleness make it more likely to craze over a thick stack of old layers. A contractor experienced with coal tar will keep coats thin. On fresh asphalt pavement, neither sealer should go down early; new asphalt needs roughly six to twelve months for its oils to cure out first.

Old Coal Tar Does Not Disappear

Switching to asphalt emulsion stops adding new coal tar. It does not remove what is already there, and worn coal tar sealcoat will continue to shed some PAH-bearing particles as it ages. Covering it with a fresh asphalt-based coat is the practical step most homeowners take. Avoid aggressively grinding, scraping or pressure-washing old coal tar residue into the street or storm drain, and if you need it removed — for example, before repaving — ask your local environmental or public works agency about handling and disposal rules, which vary.

What to Use Instead of Coal Tar

Polymer-modified asphalt emulsion is the default recommendation for most driveways. It is cheap, widely available, easy to apply with a squeegee or brush, and the added polymer narrows much of coal tar's durability lead. Our best asphalt driveway sealer guide compares the main options on solids content, coverage and reseal interval.

Acrylic and polymer sealers cost more per gallon but have low odour, low VOCs and little or no asphalt. Several are marketed for better colour retention and some resistance to fuel and oil. They are a good fit if you dislike the smell of asphalt sealer, have children or pets who play on the drive, or simply want the lowest-PAH option.

Fuel-resistant additives and oil-spot primer handle most of the reason anyone wanted coal tar on a driveway. Treat drip zones with a primer before sealing, and ask about fuel-resistant formulations if you park a leaky vehicle or store equipment on the drive.

Be careful with "coal-tar-free" claims. Some replacement products are made with steam-cracked asphalt or other high-aromatic petroleum fractions rather than conventional refined asphalt. Research from state agencies and USGS has reported that some of these can carry PAH levels well below coal tar but far above standard asphalt emulsion. A product that simply says "coal-tar-free" is not necessarily low-PAH. Look for an explicit "asphalt emulsion" or "acrylic" description, check the SDS, and where a manufacturer publishes a PAH content, prefer the low one. Some jurisdictions now regulate by PAH content rather than by naming coal tar, partly for this reason.

Whatever you choose, the application method matters more than the product. Clean, fill cracks, edge, and apply two thin coats rather than one thick one. Step-by-step instructions are in how to seal an asphalt driveway.

The Short Version

Coal tar is the tougher coating. It resists gasoline, oil and UV better than asphalt and lasts three to five years against asphalt emulsion's two to four. That is why it dominated commercial sealcoating for decades.

Asphalt emulsion is the right choice for a home driveway. It carries far lower PAH levels, smells and irritates far less, is legal everywhere, is sold everywhere, and with a polymer-modified grade the durability gap shrinks to about a year.

If you hire a contractor, specify the binder in writing. If you have coal tar already, reseal over it with asphalt emulsion after a test patch rather than disturbing it. And before buying any coal tar product, check your state and local rules, because in many places the decision has already been made for you.

Frequently Asked Questions

Related Guides