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"If coal tar is available we know it's going to produce the highest quality product we can produce and we think that's the right thing to do," Maclean says. "It is our intention to produce 100% coal tar sealer throughout 2007."

Like other sealer producers, GemSeal feels more comfortable recommending its asphalt/coal tar blend to contractors because it handles more like the traditional coal tar sealer and contractors need to make fewer adjustments.

"The most important thing with the blends or asphalt-based sealers is that the contractor and supplier need to develop a very good line of communication with each other. The contractor really needs to ask questions - how do I need to handle this differently than coal tar? How much can I dilute it? Does it contain polymers? Is it compatible with the additives I use or the previous product used?" Mariani says. "Contractors need to find out what the product can do, but more importantly they need to know what it can't do so they stay within the limitations of that product. Then they'll be able to harness all the potential that material has to offer."

One of the initial skepticisms dogging asphalt/coal tar blends was that the two materials can't be mixed. Neyra Industries, for example, does not produce a blended product because it says the two materials are from chemically different families so are basically incompatible.

"Neyra Industries Inc. does not blend asphalt and coal tar to produce pavement sealer," Conwell says. "Our years of R & D have proven coal tar contains solvent that weakens asphalt and what makes coal tar perform asphalt dilutes, to get an asphalt emulsion to perform requires modification with polymers."