Sealcoating
Coal Tar vs. Asphalt Emulsion Sealer: Which Is Better for Oregon?
Cojo
March 19, 2026
9 min read
Not all sealcoating products are the same. The two dominant sealer types in the U.S. market — coal tar emulsion and asphalt emulsion — differ in chemical composition, performance characteristics, environmental impact, and regulatory status. Which one ends up on your driveway or parking lot matters more than most property owners realize.
If you are new to sealcoating entirely, start with our guide on what sealcoating is and why it protects asphalt.
Coal tar emulsion sealer is derived from coal tar pitch, a byproduct of the coking process used in steel manufacturing. Coal tar is chemically distinct from asphalt — it contains high concentrations of polycyclic aromatic hydrocarbons (PAHs), which give it exceptional resistance to petroleum-based chemicals like gasoline and motor oil.
Asphalt emulsion sealer is derived from the same petroleum-based asphalt cement used to make the pavement itself. Refined asphalt is emulsified in water with clay fillers and chemical additives to create a sprayable or squeegeable coating. Because it shares a chemical base with the pavement, it bonds readily to the existing surface.
The chemical difference drives every other distinction between the two products.
| Performance Factor | Coal Tar Emulsion | Asphalt Emulsion |
|---|---|---|
| Fuel/oil resistance | Excellent — highly resistant to gas, diesel, oil | Moderate — softens with prolonged fuel contact |
| UV resistance | Excellent — minimal oxidation over time | Good — oxidizes faster than coal tar |
| Water resistance | Excellent | Good to excellent |
| Flexibility | Lower — can become brittle in cold | Higher — remains flexible through temperature cycles |
| Freeze-thaw performance | Good in moderate climates | Better in cold/wet climates |
| Typical recoat cycle | 3–5 years | 2–4 years |
| Color retention | Rich black, fades slower | Dark black initially, grays faster |
This is where the two products diverge sharply.
Coal tar sealers contain PAH concentrations 1,000 times higher than asphalt emulsion sealers. PAHs are classified as probable carcinogens by the EPA and are toxic to aquatic life. Research from the U.S. Geological Survey (USGS) has documented how coal tar sealant breaks down over time, releasing PAH-laden particles into stormwater runoff.
Key findings from peer-reviewed research:
Asphalt emulsion sealers contain PAH concentrations comparable to background levels found in natural asphalt deposits. While not entirely inert, their environmental impact is orders of magnitude lower than coal tar. The product is water-based, produces less volatile organic compound (VOC) off-gassing during application, and breaks down into materials chemically similar to the pavement itself.
A growing number of jurisdictions have banned or restricted coal tar sealants:
Oregon does not currently have a statewide ban on coal tar sealants. However, several factors make coal tar a poor fit for the state:
Environmental sensitivity. Oregon's regulatory framework prioritizes watershed protection. The Willamette Valley — where most of Cojo's service area lies — drains into the Willamette River, a waterway under active environmental management. Coal tar runoff introduces contaminants that conflict with state water quality goals.
Stormwater regulations. Oregon's stormwater management requirements under the Clean Water Act and state DEQ guidelines increasingly scrutinize pollutant sources. Property owners using coal tar sealants may face questions during stormwater compliance reviews.
Neighboring state precedent. Washington State's ban creates a regional norm that Oregon properties — especially those in the Portland metro area near the state border — are increasingly expected to follow.
Market availability. As bans spread nationally, coal tar product availability has declined. Major manufacturers are investing in asphalt emulsion formulations, and supply chains in the Pacific Northwest increasingly favor asphalt emulsion products.
Cojo Excavation and Asphalt uses asphalt emulsion sealers exclusively. This decision is based on three factors:
Performance in Oregon's climate. Oregon's Willamette Valley experiences wet winters, moderate freeze-thaw cycles, and relatively mild summers. Asphalt emulsion's superior flexibility through temperature changes makes it a better performer in this climate than coal tar, which can become brittle in cold, damp conditions.
Environmental responsibility. Our service area includes residential neighborhoods, schools, churches, and commercial properties that drain into local waterways. Asphalt emulsion sealers deliver effective protection without introducing PAH contamination into the watershed.
Product quality has caught up. Modern asphalt emulsion formulations with polymer additives have closed the durability gap with coal tar. Premium asphalt emulsion sealers now offer 3–4 year recoat cycles, fuel resistance that handles normal driveway exposure, and UV protection comparable to coal tar in the Pacific Northwest's UV conditions (which are far less intense than the Sun Belt states where coal tar traditionally excelled).
We apply commercial-grade asphalt emulsion sealer — not the consumer-grade product available at hardware stores. The difference in polymer content, solids percentage, and additive package makes commercial-grade product significantly more durable. For more on product quality differences, see our DIY vs. professional sealcoating comparison.
Both products can be applied by spray or squeegee, but they handle differently during the sealcoating process:
| Application Factor | Coal Tar | Asphalt Emulsion |
|---|---|---|
| Mixing | Requires heavy agitation; settles quickly | Easier to mix and maintain suspension |
| Odor during application | Strong, chemical smell; can irritate eyes and throat | Mild, low-odor |
| Dry time | 24–48 hours typical | 12–24 hours in favorable conditions |
| Temperature sensitivity | Requires 50°F+ air and surface | Requires 50°F+ air and surface |
| Worker safety | Requires additional PPE (respirator recommended) | Standard PPE sufficient |
| Cleanup | Difficult; stains equipment permanently | Water cleanup; easier on equipment |
| Skin contact risk | Avoid all skin contact (PAH exposure) | Low risk; wash with soap and water |
For most Oregon property owners, asphalt emulsion sealer is the clear choice. It delivers effective protection in the Pacific Northwest climate, avoids environmental concerns, complies with the direction of regional regulations, and is increasingly the industry standard for residential and commercial sealcoating.
Coal tar may still make sense in very specific industrial applications — fueling stations, heavy equipment yards, or areas with constant petroleum exposure — where its superior chemical resistance justifies the environmental trade-offs. But even in those cases, polymer-modified asphalt emulsion products are closing the gap.
The sealer type is only one part of a quality sealcoating job. Proper surface preparation, correct application thickness, adequate dry time between coats, and favorable weather conditions matter just as much as the product in the bucket.
Cojo Excavation and Asphalt applies commercial-grade asphalt emulsion sealer across Oregon's I-5 corridor. We handle the product selection, preparation, and application so you get maximum protection without the environmental concerns of coal tar.
Call 541-409-9848 or request a free assessment.
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