How to build a concrete countertop
The countertop rests on a base of ½-inch-thick cement board, enabling you to keep the concrete 1 inch thick except at the edges, which are just deep enough to hide the cement board. The result is a normal-height countertop that's easily supported by standard cabinets.
2) Using the sink template as a guide, cut a plug from foam insulation at least 1 1/2 inches thick to keep the sink free of concrete. A jigsaw or bandsaw works well. Sand edges of the foam and wrap them with plastic tape.
5) Along the top of the cabinet sides, screw on the scraps of wood flush with the cabinet top. Drape plastic over the cabinets and place the cement board on top. Then screw down through the board into the wood scraps using drywall screws. Attaching the board this way makes the counter easy to remove if you or a later owner wants to redecorate. Attach the foam plug in a similar way.
7) With aviator's snips, cut 2½-pound galvanized-steel stucco lath to match the countertop, minus a 1-inch gap along all edges, including all around the sink. If you need multiple pieces, overlap the mesh by a few inches.
8) Tack a board 1 inch thick along the back edge to create a guide when you screed the concrete. Plan to cover this later with a backsplash.
12) With a hammer or stick, tap along the edge band to release air bubbles. Then level the concrete with a straight board as you would for any poured project.
15) Cover the countertop with plastic. For the next three days, periodically mist the concrete to keep it damp.
17) If you see gaps that you don't like, fill them with a paste of cement and water. Allow them to harden for a few days. Polish with wet-dry sandpaper.
18) Seal and wax the counter before you use it.