Stonemasons Fife are experts at lime re-pointing of stone or brick. We only ever use lime for pointing, never cheap brittle cement.
The advantages of lime when pointing are many. Here are some:
Cement traps moisture behind it after the host masonry has been made wet with rain or condensation. When this moisture freezes it expands and pushes the cement pointing out causing cracking in the pointing to occur and ultimately it falling out all together. Lime is permeable to water and allows it to exit the masonry as it was intended to do.
Lime is designed to be used slightly softer than the masonry it supports, therefore in the case of freeze thaw movement or settlement movement etc., the lime mortar is sacrificial and will fail before the stone, thus preserving it and giving it a cushion during movement.
Lime is also more flexible than cement, and will remain intact during movement much longer than cement, as cement is a lot more brittle. Believe it or not buildings move all the time, whether it be by settlement, temperature or humidity changes, traffic vibrations and wind in the cases of chimneys and some walls. This added flexibility of lime is very important to the longevity of the re-pointing.
The bottom line? Always use lime for re-pointing, building and stone repair work.