When you build a retaining wall, offset the blocks to give the wall more stability. This means to position a full block directly over the space where two blocks meet. When you reach the retaining wall's ends, blocks must be cut in half so they do not extend past the wall's end. The best tools to use for this project are a simple hammer and chisel. The hammer and chisel easily break through the block without leaving a smooth edge that sticks out like a sore thumb from the rest of the roughened edges.
Measure the concrete block's length and divide this by two to determine the center point. For example, if the concrete block is 8 inches wide, the center point is 4 inches. You would then measure 4 inches across the block and place a chalk mark at this measurement.
Place a straight edge across the block with the edge lined up to the center chalk mark. Trace along the straight edge with a piece of chalk to make the center dividing line.
Flip the block so the chalk line faces away from you and the block stands on edge. Continue the chalk line down the block on this edge. Flip the block again so the first chalk line faces the ground and continue the straight chalk line down the block. Flip the block one final time so that the final edge faces up and finish the chalk line down this edge.
Place a chisel on the chalk line and tap the handle with a hammer to score the block. Lift the chisel and place it on the chalk line, in front of the score you just made. Tap it with a hammer again. Continue until you score the entire side. Score along one long side and both shorter edges, then flip the block over to the unscored long side.
Set the chisel's edge on the chalk line. Score along the chalk line, down the entire side. Set the chisel's blade into the scored line. Give the chisel's handle a firm tap with a hammer. The concrete block should split into two parts.
Check that the block broke at the desired point. Use the chisel and hammer to break off any excess block along the edges to make a cleaner break.