Use expansion joints with concrete by placing them at the recommended distance when making the pour. For existing concrete without expansion joints, cut an opening using a concrete saw and install the joint. Narrow concrete surfaces, such as sidewalks, normally do not use expansion joints. They use narrow grooves you make with a special trowel when finishing the concrete.
When pouring concrete, add expansion joints at the edge of each section of the pour. Possible materials include rubber, wood or cork. Purchase joint materials that match the thickness of the pour and attach them to the forms to ensure they remain upright.
The joint trowel creates a groove without extending the opening through the concrete. This groove provides sufficient space for the expansion of the top of the concrete without cracking. It works well with narrow pours, but wider ones, such as driveways, do best with expansion joints.
If the concrete finisher left the expansion joints out of the work, it is possible to add them later. Mark the position of the joint and use a chalk line to make a straight mark across the surface. Use a cement saw to make the cut. It should be perpendicular to the sides of the driveway.