Coal Tar or Asphalt Emulsion: What Should Go On a Waukesha Driveway

Most homeowners think of sealcoating as a single product. It is not. There are two broadly different chemistries sold as driveway sealer in this country, they look nearly identical going down, and in the Milwaukee metro one of them is illegal in about two dozen municipalities while the other is not. That is an unusual situation, and it makes the choice of sealer a genuinely local question in Waukesha County rather than a matter of taste.

This is not a fringe environmental argument either. The evidence that drove those ordinances came from federal researchers sampling streambeds in this specific metro, and the results were strong enough that the Milwaukee Common Council voted 15 to 0 to ban high-PAH sealants. The City of Waukesha has not passed an ordinance of its own, which means Waukesha property owners are the ones making the decision. Here is what is actually in each product and what the local record says.

What Is Actually In a Bucket of Driveway Sealer

Coal tar sealer is built on refined coal tar pitch, a byproduct of turning coal into coke for steel making. Asphalt emulsion sealer is built on asphalt - the same petroleum-derived binder that holds your driveway together - suspended in water with clay and additives. Both are squeegeed or sprayed on, both cure to a dark, uniform finish, and to the eye there is very little difference on day one.

The difference is in the polycyclic aromatic hydrocarbons, usually shortened to PAHs. Coal tar pitch is naturally very high in them. Asphalt is not, by a wide margin. PAHs are the reason the ordinances exist: several are classified as probable human carcinogens, and they are persistent, meaning they do not break down quickly once they leave the pavement.

The leaving is the mechanism people miss. A sealed driveway sheds a fine dust as it wears - abraded by tires, shovels, and plow blades. That dust washes into the storm drain, the storm drain goes to a creek, and PAH-bearing particles settle into the sediment where they stay. In a Wisconsin winter, with months of plowing and shoveling directly on the coating, there is a lot of abrasion.

What the USGS Found in Milwaukee-Area Streams

In December 2016, U.S. Geological Survey researchers working with the Milwaukee Metropolitan Sewerage District published a study in Environmental Toxicology and Chemistry based on sampling at 40 streambed sites across the Milwaukee area. Their finding was blunt: coal tar sealcoat accounted for 42 to 94 percent of the PAHs in the sediment they sampled, with the remainder attributable to coal combustion and vehicle emissions.

The most contaminated sites they identified included Lincoln Creek, Underwood Creek, and the West Milwaukee Ditch, where 78 percent of sediment samples carried PAH levels considered harmful to aquatic organisms. These are not remote waterways. Underwood Creek drains the suburbs on Waukesha County's eastern doorstep, the same kind of subdivisions that Waukesha, Brookfield, and Elm Grove are made of.

That study is what moved the ordinances. It is worth noting what it did not say: it did not claim asphalt emulsion sealer is harmless or that sealcoating is a bad idea. It identified one specific ingredient as the dominant local source of a specific contaminant, and municipalities responded by restricting that ingredient rather than the practice.

The Ordinance Map Around Waukesha

Milwaukee banned the sale and use of high-PAH pavement sealants on February 7, 2017, by a unanimous Common Council vote, with a threshold of 1 percent PAH by weight. Dane County had already restricted them roughly a decade earlier, the first Wisconsin jurisdiction to do so.

Closer to home, the Village of Elm Grove - inside Waukesha County - adopted its ordinance effective August 28, 2017, prohibiting the application, sale, and display of sealants containing more than 1.0 percent PAHs by weight, with retailers required to post notices. Across the county line, West Allis tightened its rule in 2025 to a 0.1 percent threshold, with forfeitures of $500 to $1,000 and each day of violation treated as a separate offense.

The published national list of coal tar bans records roughly two dozen Wisconsin municipalities plus Dane County, including Wauwatosa, Greenfield, Greendale, Hales Corners, Franklin, Oak Creek, Whitefish Bay, Shorewood, Glendale, Brown Deer, Bayside, St. Francis, Racine, Green Bay, Sheboygan, Manitowoc, and Port Washington. There is no statewide Wisconsin ban in force. Minnesota, by contrast, went statewide in 2014 after 29 local bans.

The City of Waukesha is not on that list. Neither is Brookfield, Pewaukee, New Berlin, or Delafield. That does not make coal tar a good idea in Waukesha; it makes it your call rather than the city's. Given how many crews work across the Milwaukee County line where it is prohibited, a great many contractors in this metro already run asphalt emulsion exclusively - you simply have to ask.

Does Asphalt Emulsion Hold Up in a Wisconsin Winter?

This is the honest objection, and it deserves a straight answer rather than a slogan. Coal tar sealer has a real reputation for chemical resistance, particularly against fuel and oil drips, and for a somewhat harder finished surface. Those are not imaginary properties.

But the load a Waukesha driveway carries is not primarily chemical. It is water, salt, UV, plow abrasion, and about 42 freeze-thaw crossings a year for the Great Lakes region as a whole. Against that combination, a properly applied two-coat asphalt emulsion job over clean, crack-filled pavement performs on the same two-to-three-year rotation you would expect from any coating in this climate. The variable that actually decides how long a coat lasts here is prep, not chemistry - and it is not close.

There is a practical argument too. Asphalt emulsion is asphalt-based, which means it is chemically closer to the pavement it is protecting. And in a metro where nearby municipalities set forfeitures of $500 to $1,000 per day for applying the alternative, a crew that has standardized on emulsion is one that can work everywhere without keeping two products on the truck.

What to Ask the Crew Before They Start

Four questions settle it. First: is the sealer coal tar based or asphalt emulsion based? A crew that cannot answer immediately has not thought about it, which tells you something on its own. Second: can I see the product label or the safety data sheet? Both list the base material plainly.

Third: how many coats, and what is the coverage rate? Two coats is standard, and stretching material thin is the quiet way a low bid gets made. Fourth: what prep is included - cleaning, edging, oil-spot priming, crack filling? Prep is where the difference between a three-year coat and a one-year coat actually lives, and it is invisible in a finished photograph.

None of those questions is confrontational and none of them requires you to know chemistry. They just make the quote comparable across bidders. Once you have the answers, the cost page will tell you whether the number in front of you is in line with the market, and the winter pavement data will tell you whether the timing makes sense for the season you are in.