Measure your cabinets, adding about ¾" on all sides to allow for overhang to determine the size of your countertops.
Cut particle board strips to attach to the ends of the mold to create your countertip sides. Cut them 2¾" wide or as wide as you would like the thickness of your counters.
Carefully wipe down the bottom of your countertop molds to ensure there isn't dust or debris that would mar your counter surface.
Tape and caulk the seams of the mold.
Cut pieces of rebar.
Mix and pour the concrete. Fill the mold half-way. Add rebar, then pour the remaining concrete.
Level the top layer of concrete.
Bang the bottom of the mold with a hammer to make the air bubbles rise to the surface and help prevent cracks.
Allow the concrete to cure for at least a week before removing the mold and installing your new countertops.