Polystyrene foam is one good material for making custom molds. Stone Soup Concrete in Florence, MA

Countertop makers use such materials as Plexiglas, polystyrene foam, urethane rubber (see Making Molds from Rubber), Formica, and even Lexan to make their own molds. "We will use urethane foam and sculpt it to the shape we want it and then jacket it with an epoxy shell," says Mike Karmody, Stone Soup Concrete. "That's what we did on the black island."

On another recent project, a white concrete kitchen countertop, Karmody used Plexiglas laminated onto a plywood mold. They then welded the edges and polished, starting at a 150 grit and finishing with a 1500 grit, then used rubbing compound to get it perfectly smooth. The sink is drafted about 3 or 4 degrees on the sides and the bottom tapers about ¼ inch to the drain point.

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