Get a form, or a mold, for the curb. A curb form is a trough-shaped box with a cavity in which to pour concrete. The shape of the cavity determines the shape of the curb. It is possible to build concrete forms with plywood. Rain gutters with gutter caps at the ends also make suitable curb forms. For a more organic or handmade appearance, model a curb form out of clay.
Seal any seams or joints in the form, stuffing clay into them. Paint the inside of the form with a liberal amount of vegetable oil or oil soap. The oil acts as a release agent.
Prepare fast-setting, pre-blended concrete, according to the manufacturer's directions. Add tint to the concrete to match or complement the color of the pavers. Pour concrete into the form. Tap lightly all around the sides to settle the concrete. Screed the top of the form with a board to ensure that the bottom of the curb will be flat and even.
Allow the concrete to harden for 20 to 30 minutes, then remove the concrete curb from the mold. Cover the curb loosely in plastic and spray regularly with water for a couple of days while the concrete finishes curing.