Bricks, Masonry, Asphalt and Concrete - mortor/cement to a fieldstone foundation

Let me see if I can keep this short. I have a section of a basement that is fieldstone and old mortor/cement. I'm trying to gouge out section of the old mortor and back fill it with hydraulic cement. I am receiving water at this section. What I would like to do is make the wall smooth, I want to fill in all the voids between the stones with a mortor or a cement. I know before I slab this material on all the loose material needs to be removed, such as with a wire brush. But in a perfect world I would love to dig down on the outside and seal the foundation from the out side, thats for another day. Do I need to prep the stones with anything first? I'm concerned by the consant moisture from the outside ground the mortor or cement will eventually pull away from the wall within a few years.