Cement For Concrete Countertops. A specially formulated flow able high strength concrete mix. Apply the sealer according to package instructions.
Whether you use a bagged mix specifically designed for concrete countertops, or mix your own, mix design is critical for concrete countertops. This process makes it possible to create a countertop in any shape and color. The countertop mix comes in ready to use bags where all the dry materials have been combined for ease of use, all you have to do is add the water.
Make sure the mold is on a level surface that can accommodate the weight of the concrete.
The versatility of concrete allows the material to be molded and cast in almost any shape, size, thickness and color.
Using rubber cement or another strong, even-drying adhesive, glue the foam cutout for your sink to the location it will go for the counter. There are several sites on the net with good instruction and lots of details, including one here on Instructables. Concrete can be cast into any shape and pigmented, stained, or textured with all kinds of shades and finishes; you can even embed tiles, stones, etc.