Asphalt Knowledgebase | FAQs Regarding Sealcoating

Sealcoating extends the useful life of the capital asset—an asphalt parking lot—by protecting the pavement from the natural aging process caused by sunlight, water and debris. Sealcoat also protects pavement from degradation caused by leaking oil, gasoline and other caustic products. An added benefit is that sealcoating adds to the “curb appeal” of a paved surface, giving it a clean, uniform look.

There are two essential options for sealcoating: refined coal tar-based sealers and asphalt-based sealers.

There are two essential options for sealcoating: refined coal tar-based sealers and asphalt-based sealers. Other options are cost-prohibitive for most applications.

Refined coal tar-based sealers are produced from selectively refined fractions of crude coke oven coal tar, which is a byproduct of the metallurgical coke-making process. Metallurgical coke is required to produce Basic Oxygen Furnace (BOF) steel. As coal is converted to coke in the coke oven, coal tar is generated as a byproduct, and this material is referred to as “crude coal tar”. Just like “crude oil”, crude coal tar serves as a raw material that is distilled into many different fractions in coal tar refineries. The different fractions are then used to make many different products, including refined coal tar-based
sealers.

The majority of pavement sealers are an emulsion, a mixture typically consisting of water, clay, sand, polymers and usually less than 20% of either asphalt or refined coal tar.

Pavement sealers have been applied for over six decades. Sealing is a tried and true way to protect and beautify a pavement, prolonging its useful life and minimizing the need to replace the asphalt, which consumes a lot of energy (fuel to manufacture, deliver and install) and natural resources.

Most sealer manufacturers make both refined coal tar-based products and asphalt-based products. Even though most sealer manufacturers make both, most recommend refined coal-tar based for most applications because the superior performance of tar-based sealcoat allows the manufacturers to stand behind the performance of their products, enhancing the reputations of their businesses. Research and development projects continue to improve the performance of asphalt-based sealer, but there remains a way to go.

Asphalt-based sealers have many of the same beneficial properties as refined coal tar-based sealers. The tar-based product, however, is superior in strength, resistance to leaks/spills of petroleum products, UV bleaching and road salts.

Refined coal tar-based sealers (1) protect the underlying asphalt pavement from leaking oil and gas spills, (2) last longer than asphalt-based sealer, (3) are more resistant to natural aging processes caused by exposure to the elements (sun, rain, freeze-thaw, etc.), (4) adhere (that is, “sticks”) to the underling pavement better, and (5) are manufactured to a performance-based specification (ASTM® D490).

Air sampling studies showed refined tar-based sealers pose insignificant inhalation risk to applicators, manufacturers or the general public. Coal tar is listed by the US Food and Drug Administration (FDA) as “generally recognized as safe and effective” active ingredients for use to treat these skin ailments (dandruff, psoriasis, eczema) with coal tar concentrations up to five percent in over-the-counter products. In fact, millions of people worldwide use coal tar soaps, shampoos and creams approved for use as over-the-counter medicines. Research with insurance carriers shows a general lack of insurance claims over the history of sealant use.

Some activists say that refined tar-based sealers are a health threat, but generations of family-owned companies in the business of making or applying sealcoat have zero reports of adverse chronic health effects—including cancer—that can be attributed to exposure to sealcoat.

Many studies have been performed over nearly a century to see if patients who intentionally expose themselves to high-level doses of coal tar for long periods of time have increased risk of cancer. All the studies have reached the same conclusion—there is no evidence of cancer.

Activists point to the US Geological Survey (USGS) research to claim that sealants are the main source of polycyclic aromatic hydrocarbons (PAHs) in the environment. However, the USGS has been shown to have manipulated data and used circular reasoning in their sealant studies. Independent studies of New York Harbor and Puget Sound (Seattle) found sealant contributes less than 1% of PAHs to sediments in those locations. A recent independent statistical study of the Illinois River by the Universities of Illinois and Milwaukee-Wisconsin suggested a sealcoat contribution of no more than a few percent. The independent studies are consistent with industry-funded analyses.

Refined tar-based sealer has a very distinct odor, and the human nose is able to detect it at extremely low concentrations. The smell is primarily the presence of naphthalene, which has an odor threshold about three parts per billion (ppb), a very low concentration. To put this into perspective, the odor threshold for nail polish remover is 7,000 ppb. The American Conference of Governmental Industrial Hygienists states that the level of naphthalene that is considered safe for workers is ten thousand ppb. Therefore, the difference between being able to smell it and worrying about it is huge.

Air sampling studies showed refined tar-based sealers pose insignificant inhalation risk to applicators, manufacturers or the general public. In fact, millions of people worldwide use coal tar soaps, shampoos and creams approved for use as over-the-counter medicines to treat skin disorders such as eczema and dandruff. Research with insurance carriers shows a general lack of insurance claims over the history of sealant use.

For the same reason that exterior painting is not recommended in cold or wet weather, sealcoat is not applied in those conditions because the water in the emulsion won’t evaporate. If the water doesn’t evaporate, sealcoat particles can’t begin the curing process of sticking to each other and the coated surface.

Dried sealcoat does not wash off. If any sealcoat (asphalt-based or refined tar-based) washes off before it dries, it can suffocate fish. The fish are NOT poisoned. Autopsies have shown that the fish die because sealcoat particles cover the fish’s gill plates.

Like latex paints, sealer is applied as a water-based emulsion. All emulsions contain water. Evaporation of the water starts the process of “sticking” the sealcoat particles to each other and to the coated pavement. Sealer that is dry to the touch means that the surface can be open to foot traffic, but not vehicle traffic. Sealcoat can be driven on once the process of curing is well underway, meaning that the sealer particles are sticking to each other and the pavement. Curing takes more time than drying because it takes longer to drive out moisture that remains after the initial drying.