I have read through a number of threads on fieldstone foundation repair and have seen the consensus for using straight lime or "low portland" mortars for this work. I have a old stone foundation that has a couple medium sized cracks - 1/4" wide or so. There are also a couple places where the old mortar has fallen away and revealed a gap that appears to go pretty deep into the foundation.
I was originally thinking of squeezing grout into those deep gaps and letting gravity take it from there. Now, knowing that I should avoid portland cement, I need to figure out the best way to work a lime mortar into the deep recesses of the foundation. From people's descriptions I assume that it wouldn't flow the way that grout would.
On the whole, the foundation is pretty sound, but I'd like to tighten things up where I can.