will really depend on the condition of the stone as to how long any water will take to make ingress into the property,remove the cement pointing and re-point with 3.5 N.H.L lime mortar,their is no cement or additives, it is hydraulic lime , NOT HYDRATED. it is available from varies outlets on the net you can buy it in tubs or bags usually delivered to your door so you can purchase to suite your pocket. although the overnight temperature is still a little bit to erratic to carry it out at this time of year.

GOOD LUCK ALEX

Hi there, apart from sealant being painted on stone work which you have already done, the proper way would have to have used hydraulic lime 2m grit and washed sand. As using lime allows for movement expansion and contraction and does not crack as lime really does not go off forms a hard top layer as it gradually weatheres. But using cement will not do the same thing going hard and in many cases stronger than the stone which when you experience expansion the cement will either pull the face off the stone or leave gaps behind the stone allowing in water causing damp and in winter when it freezes blows the pointing.
Thanks, tom limestone construction and masonry