Low-cost screening for coal tar content

Where it still occurs, coal tar sealcoat is primarily applied to non-road pavement: driveways, parking lots, trails, schoolyards. The best information available is that state governments in the U.S. do not use materials containing coal tar on the roads they maintain. Local governments tend to follow their state’s lead on pavement maintenance, but the material choices local governments are making either for chip seals (gravel over sealant) or sealcoat-only applications are difficult to track.

As a result, citizens or other stakeholders may question whether coal tar-based sealant has been used, either in violation of a ban, unbeknownst to a pavement owner, or in any setting in which there may be localized health or environmental impact concerns. A low-cost solvent screening test developed by the City of Austin, Texas can be a good place to start in answering these questions.

If a recent sealcoat application has a strong mothball-like odor, the Austin test has proven to be a reliable method to check for coal tar content. It requires collection of pea-sized samples of the top layer of sealcoat, with care taken to scrape or shave off a thickness similar to about 2 sheets of paper. See the rest of the test on the City of Austin Web site. Follow the directions and look for color changes as pictured below.

Coaltar sealant test color tubes, photos courtesy of Tom Ennis at

Scraping test results (left to right): dark brown/black color: likely to be asphalt-based; reddish color: likely has some coal tar present; yellowish color: likely to be coal tar-based. Scraping description and photos courtesy of Tom Ennis.

The Austin method has proven to be very accurate and resistant to error due to its simplicity. However, if a screening test indicates coal tar is present, certified laboratories can be used to verify that result. Multiple lab analyses for a given surface are suggested to produce the most reliable result.