Strengthen a wall by filling it

A narrow wall section like this can be strengthened with concrete and rebar in one or more block cells. Mix a batch of concrete that is wet enough to pour easily. Pour in a foot or so of concrete. Cut a piece of rebar to the height of the wall minus an inch or so and insert it into the center of the cell. Fill the cell the rest of the way with concrete. For extra strength, you can use this method on some or even all of the cells.