When repointing the mortar removed would be twice the width of the chase aprox 25mm.  Then pointed with new mortar 4 - 1 ratio.  

REPOINTING and TUCKPOINTING

Tuckpointing is a way of using two contrasting colours of mortar in the mortar joints of brickwork, one colour matching the bricks themselves, to give an artificial impression that very fine joints have been made.