After wetting the surface to be repaired, a "peanut butter coat" is applied. This is a mushy mix, with a consistency that gives it that name. This is much wetter than you want for the entire repair (it would never hold a shape), but you want this between the repair material and the surface of the concrete. Just like the water you splash on before applying any mortar, this moisture in this coat is absorbed into the existing concrete. By drawing in that moisture it helps that bond between the repair and the underlying concrete to form securely...Otherwise the repair would just pop out...