Do not remove so much that the structure becomes unsafe. If necessary do small sections at a time and re-point before continuing. Generally the use of wedged galleting stones will secure a wall whilst raking out. When the lime putty is fully soaked, the final mortar can be mixed. Samples of the old mortar should be used as a guide to the composition and texture to be aimed at.
Most old mortars are a mix of lime putty, lime sand, and grit.
Generally a greater proportion of lime is used for sandstone or sedimentary rocks and a harder mortar use for granite or impervious rocks. The sort of building sand commonly available from builders merchants to-day was not used. Often rough sand would have been cut from a local source, and a great saving can be achieved by exploring the locality or asking old sages where sand was obtained. In non-clay areas, subsoils can often be sieved to provide a workable aggregate. Grits were often obtained from rivers in which case the particles are of a rounded form.