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Vance says his company tells contractors exactly what they're getting, and they let contractors know if the percentage formula changes from one delivery to the next.

"If it changes from 80/20 (80% coal tar to 20% asphalt) to 75/25 the contractor won't notice much of a difference and the material won't act differently. But if we were to go from 80/20 to 20/80 they would notice a huge difference and would need to alter their operation accordingly," Vance says. "A blend heavy in coal tar will act more like coal tar sealer and a blend heavy in asphalt will act more like an asphalt sealer. With an 80/20 blend they won't notice much difference from pure coal tar."

Bill Maclean, at The Brewer Co., which produces coal tar sealer for the contractor market and an asphalt-based sealer for the retail market, produced a blended product last year simply out of necessity.

"We produced a blend last year to make certain we had enough material to help our customers keep working," Maclean says. "It is our view that, even with technology that has become available in the last few years, any blend of asphalt and coal tar is a compromise with material that is 100% coal tar. For us, the issue last year was that if we didn't produce a blended product the people that rely on us for their livelihood would be short the material they needed."

Maclean says that based on what The Brewer Co. has been told by its RT-12 suppliers this year they don't expect to face a coal tar shortage in 2007.