Horizontal line at the end of data list

I have a changing table of data contained in C6:I56, I want a horizontal line at the bottom of my list. When a new line of data is entered I want the line automatically at the bottom of the last row of data C:I.

in essence cells C6:C56 determines the end of the list, the first blank cell between C6:C56 is the end of my list, so I need a thick horizontal border line here, C to I.

thanks