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"Asphalt sealer is just not as forgiving as coal tar sealer. You can't over-dilute asphalt emulsion and expect optimum performance," Conwell says. "Coal tar is a little more forgiving. This is something we explain very carefully to contractors making the switch."

Conwell says Neyra's 2007 asphalt emulsion pavement sealer will want more aggregate rather than less, going from 3 lbs. of silica sand per gallon to 5 lbs. per gallon.

"The additional aggregate improves the performance of our sealer," Conwell says. "It will dry faster, the additional sand improves skid resistance, and it will help it last longer. We really hammer hard to our contractors that they need to use the right sand and the right amount of sand to get the best performance out of our products."

Mariani cautions that another difference between the asphalt and coal tar sealers is that asphalt-based sealer is much more negatively susceptible to moisture and high humidity than is coal tar.

"With coal tar contractors sometimes push the limits of the material because they've established a comfort level over time with its expected performance," he says. "But if they push the limits with asphalt-base sealers, which are more fragile than coal tar, they very well could encounter consequences not otherwise experienced in the past using coal tar. It's very important that they stay strictly within the limitations of the material as far as mix design and weather conditions are concerned."