Use a chisel and hammer to break off any loose or cracked areas in the concrete. Use a power washer to remove all the debris from the surface of the driveway. If the concrete has grease stains, wash them with a mixture of four or five drops of dish detergent mixed in a gallon of water. Rinse well. Allow the surface to dry completely before proceeding.
Build forms to hold the overlay in place. They may be scrap lumber, or you can use 1-inch by 4-inch furring strips. Brace them against the existing concrete at the right height by placing wooden stakes in the ground to hold them. Use a carpenter's level to make sure the forms are level.
Mix Portland cement with water to the consistency of paint. Dampen the cement slab. Use an old paintbrush to spread the cement paint over the surface of the driveway. This acts as a bonding agent for the cement overlay.
Mix one part sand, two and a half parts Portland cement and water to form a thin overlay. If you are pouring a thicker overlay, you may add three measures of gravel to the mix. Add color to the mix at this time if you're coloring the concrete.
Pour the overlay mixture on the driveway surface before the cement paint dries completely. Use a rake to push the mixture into corners and other areas where it doesn't naturally flow.
Level the surface by pushing a long, straight board back and forth across the top of the forms. Add more overlay if necessary to any low spots.
Use a float to smooth the surface. Add a curing compound to the surface as soon as the surface is the way you want it. If you prefer, spray nonstick spray on concrete stamping tools and stamp the concrete overlay.