There are times when you might need to patch concrete such as when you have a crack in your sidewalk. The first step is to clean out the crack thoroughly with water and then use a chisel to slightly widen the crack to prepare it for the patch. You can purchase a concrete patch adhesive that you can brush inside the crack that will help the patch to take. You then purchase concrete patching material or mix up your own and pour into the crack. Tap it slightly to make sure the hole is fully filled. Once full, smooth over. Allow the patch to dry for 2 hours and then cover it with plastic and a board. Leave it covered for about 5 days, watering it down a bit each day.