Asphalt parking lots and driveways are significant capital investments that increase both the value and functionality of a property. Like any infrastructure investment, the asphalt surface must be maintained to preserve value and performance over time. Maintenance options include resurfacing or replacing the asphalt periodically, or extending the service life of the pavement through sealcoating, which greatly reduces long-term resurfacing and replacement expenses. Understanding the fundamental differences between the two primary sealer types is essential for contractors making informed recommendations. For contractors seeking deeper knowledge of asphalt systems, Asphalt Pavement Engineering Mix Design Construction Methods Rehabilitation offers a comprehensive examination of the broader pavement engineering context. Sealcoating extends the useful life of asphalt pavement by protecting it from natural aging processes caused by sunlight, water, and debris, while also adding curb appeal with a clean, uniform appearance.
Understanding the Two Primary Sealer Types
The pavement maintenance industry relies on two essential options for sealcoating: refined coal tar-based sealers and asphalt-based sealers. Each type has distinct chemical origins, performance characteristics, and application considerations that contractors must evaluate when selecting products for specific job requirements.
Refined Coal Tar-Based Sealers (RTS)
Refined coal tar-based sealers (RTS) are formulated from a selectively refined fraction of crude coke oven tar, which is a byproduct of the steel making process. This industrial origin gives RTS unique chemical properties that translate into specific performance advantages on pavement surfaces.
Asphalt-Based Sealers (ABS)
Asphalt-based sealers (ABS) are based on a selectively refined fraction of crude petroleum oil. While other sealer options exist in the market, they remain cost-prohibitive for most commercial and residential applications, making ABS and RTS the two practical choices for the vast majority of sealcoating projects.
Performance Comparison: RTS vs ABS
There are several important differences between refined tar-based sealers and asphalt-based sealers that directly affect pavement protection outcomes. Understanding these distinctions helps contractors choose the appropriate product for each project’s specific conditions and performance requirements.
Fuel and Chemical Resistance
The most significant performance difference between RTS and ABS is fuel resistance. RTS protects the underlying asphalt pavement from leaking oil, gas spills, and other petroleum products. These petroleum derivatives are chemically and physically similar to the petroleum from which the asphalt itself is derived. ABS cannot, by definition, be fuel resistant, making RTS the preferred choice for parking lots, gas stations, and areas where vehicle fluid leaks are expected.
Weather and Environmental Resistance
RTS offers greater resistance to natural aging processes caused by exposure to the elements, including sunlight, rain, and freeze-thaw cycles. The molecular structure of refined coal tar provides inherent durability that withstands UV degradation better than petroleum-based alternatives. This translates into longer intervals between recoating applications and better long-term pavement protection.
Adhesion and Cohesion Properties
Refined tar-based sealers demonstrate stronger cohesion, meaning the material sticks to itself more effectively, and stronger adhesion to the underlying pavement surface. These properties reduce the likelihood of delamination, peeling, or premature wear, particularly in high-traffic areas where mechanical stress on the sealcoat is greatest.
Standards, Specifications, and Manufacturing Considerations
Industry Specifications
RTS products are manufactured to a performance-based specification defined by past federal specifications and now ASTM specifications using ASTM approved testing protocols. This means refined tar-based sealers must meet consistent, measurable quality standards to be sold in the market. In contrast, there is no industry-accepted ABS formulary, performance testing protocol, or specification, creating variability in quality and performance among asphalt-based sealer products.
Manufacturer Recommendations
Most sealer manufacturers produce both refined coal tar-based products and asphalt-based products. Despite offering both options, the majority of manufacturers recommend RTS for most applications because the superior performance of tar-based sealcoat allows them to stand behind their products with confidence, enhancing their business reputations. Ongoing research and development projects continue to improve the performance of ABS, but significant gaps remain.
Health, Safety, and Environmental Considerations
Contractors frequently encounter questions about the safety profile of refined coal tar-based sealers. A thorough examination of the available scientific evidence provides important context for these concerns.
Human Health Studies
Across the two-, three-, and four-generation memories of the many family-owned companies in the sealcoating business, there are no reports of adverse chronic health effects that can be attributed to exposure to sealcoat. Expanding the search to other products made from refined tar, millions of people worldwide use coal tar soaps, shampoos, and creams approved as over-the-counter medicines to treat skin disorders such as eczema, psoriasis, and dandruff. Coal tar and its derivatives are listed by the U.S. Food and Drug Administration (FDA) as generally recognized as safe and effective active ingredients for use in treating these skin ailments, with coal tar concentrations up to 5% in over-the-counter products. Studies conducted over nearly a century have found no evidence of cancer in patients who intentionally expose themselves to high levels of coal tar for extended periods.
Understanding PAHs
Controversies about RTS safety often center on polycyclic aromatic hydrocarbons (PAHs), which are components of coal tar-derived materials. However, PAHs occur naturally and are produced whenever organic material is heated or burned. Smoke from forest fires, wood-burning fireplaces, decaying plants in swamps or compost piles, emissions from vehicles, cooking food, and even volcanic eruptions all contain PAHs. Studies performed in 1991 by refined tar producers, emulsion producers, and contractors using both spray and squeegee application methods proved that PAH exposures during sealcoating were well below and sometimes unmeasurable using OSHA evaluation methods and established threshold limit values.
Aquatic Safety
Dried sealcoat does not wash off and is no longer sticky. If any sealcoat, either asphalt-based or refined tar-based, washes off before it dries, it can suffocate fish and other aquatic life. Fish are not poisoned by sealcoat; autopsies have shown that suffocation occurs because sealcoat particles cover the fish’s gill plates. Dried sealcoat particles are not bio-available to people or most other species.
Practical Application FAQs for Contractors
Why Is RTS Less Common on the West Coast?
Crude coal tar is a byproduct of steel making. The steel industry is largely located east of the Rocky Mountains. Coal tar refineries that produce the base material for RTS are situated near historical steel manufacturing centers. Transportation costs make locally produced asphalt-based sealers the more cost-effective choice on the West Coast, while RTS remains competitive in the Midwest and East.
Cost Comparison
All else being equal, asphalt-based sealers are generally cheaper on the West Coast due to transportation factors, but not in the Midwest or East. ABS pricing is more volatile as it fluctuates with crude oil prices. Additionally, the manufacture of refined tar-based emulsion is a single-stage process, while ABS typically requires additives for biocides, color, and ultraviolet light resistance, adding to material costs.
| Property | Refined Tar Sealer (RTS) | Asphalt-Based Sealer (ABS) |
|---|---|---|
| Chemical origin | Refined coke oven tar (steel byproduct) | Refined crude petroleum oil |
| Fuel resistance | Excellent protection against oil, gas, petroleum | Not fuel resistant by definition |
| Industry specification | ASTM performance-based specification | No accepted formulary or testing protocol |
| Weather resistance | Superior resistance to UV, rain, freeze-thaw | Moderate; requires UV additives |
| Adhesion and cohesion | Strong adhesion to pavement and self-cohesion | Generally lower adhesion and cohesion |
| Manufacturing stages | Single-stage emulsion process | Requires biocides, colorants, UV stabilizers |
| Price stability | Relatively stable pricing | Volatile, tied to crude oil market |
| Geographic availability | Competitive in Midwest and East | Cost-effective on West Coast |
Drying vs Curing
Like latex paints, both RTS and ABS are applied as water-based emulsions. Evaporation of water starts the process of adhering the sealcoat particles to each other and to the pavement. Sealer that is dry to the touch can be open to foot traffic but not vehicle traffic. Sealcoat can be driven on once the curing process is well underway, meaning the sealer particles are sticking to each other and the pavement. Curing takes longer than drying because additional time is needed to drive out moisture remaining within the coating after the initial surface drying.
Understanding Sealcoat Odor
The distinctive odor of refined tar-based sealer is easily identifiable. The human nose can detect it at extremely low concentrations, primarily due to naphthalene. The odor threshold for naphthalene is below three parts per billion (ppb). For perspective, the odor threshold for nail polish remover is 7,000 ppb, which is 2,333 times greater. According to the American Conference of Governmental Industrial Hygienists, the safe worker exposure level for naphthalene is 10,000 ppb. The difference between being able to smell it and having a health concern is substantial, and the odor fades quickly as the sealcoat cures.
Weather Application Requirements
Sealcoating is not recommended in cold or wet weather for the same reason exterior painting is not advised under those conditions: the water in the emulsion will not evaporate. If water does not evaporate, sealcoat particles cannot begin the process of adhering to each other and the pavement surface. Contractors should plan applications during favorable weather windows with temperatures above 50 degrees Fahrenheit and no rain in the forecast for at least 24 hours.
Understanding the differences between refined tar sealers and asphalt-based sealers enables contractors to make informed decisions based on project requirements, geographic location, and performance expectations. For more on pavement maintenance techniques, explore Tearing Up the Pavement Modern Cold Milling and removal equipment. Contractors working with broader building envelopes may also benefit from reviewing Residential Glass Technology Low E Coatings Gas Fills for energy-efficient glazing considerations, and Mivan Formwork Technology for modern construction forming systems.