Cutting concrete with your hands requires the use of a masonry chisel and hammer. This is a very physical task that requires skill and precision in order to avoid cutting too much concrete or causing it to crack unnecessarily. It can be a simple task to complete and as easy to perform as sawing a piece of wood.
Be sure to always wear protective equipment when cutting concrete, including safety glasses and gloves.
Mark the Cut Area
Use a pencil to draw the area that will be cut away from the concrete. The outer area is what you will be leaving behind, so be sure to mark the area as accurately as possible.
Use a Hammer and Chisel
In one hand, take a chisel and place the edge at one end of the mark in the concrete. Hammer the chisel into the concrete, and continue doing so until you have formed a groove. Several consecutive blows should do the trick.
Then repeat the process at the other end of the cut mark until the groove forms a channel.
Use an Angle Grinder
After creating the groove, use an angle grinder to begin cutting into the groove along the mark. After several passes, you should successfully complete your cutting.