Flint wall mortar mix

[handyman]

Can anyone help me with a mortar mix for a small repair to my flint wall. I want to match the existing finish as much as possible, but am finding that information on this is hard to come by. The wall has previously been bodged in a couple of places where someone has used a sand/cement mix which looks bad, can this be fixed ?
Thanks

 

[Pford75]

Our builder used 3.5:1 non hydraulic:washed sharp sand.

You may find that colour matching is tricky as the surrounding mortar is weathered with dirt/grime. We had some success with coal dust in some patch repairs...although only time will truly weather