In reply to 1234None:
I've repointed 2 chimney stacks, rebuilt an internal wall and various bits of sleeper walls in my victorian house with lime mortar / limecrete. If it's decorative pointing of brickwork and not really structural then use NHL2 lime in your mortar to stop it ripping the skin off the bricks if you have to remove it in the future. NHL2 is the weakest type of lime and thus best used for plastering and non-structural pointing. It is the whitest though in case colour is important.
Making mortar - make it drier that you think and leave it for some time before trying to use it. It takes time & mixing for the mortar to attain optimum workability, so if you mix it to a workable consistency straight off it will have too much water in it and will become sloppy then crack when it dries. So mix it too stiffly, leave it half an hour, then mix it again and add water sparingly to get the right consistency. Use a round-ended gauging trowel for your mixing. I'm asuming you're not going to use a mixer, but if you were, be aware that they tend to cause balling unless it's the horizontal type. I'd use a large yoghurt pot as my measure and do about 4 pots' worth of sand/lime (I can't remember ratio, look it up on the St.Astier website) in a bucket, mixed completely dry then add water and so on. It was hard work to get the workability of the mix. I'd do two mixes and leave one 'settle' whilst I used the other, then start another mix whilst using the second. That way I always had a mix settling.
You'll need to spray the bricks with water a lot beforehand to stop them sucking the moisture out the mortar before it's had a chance to chemically harden. I'd still spray the pointed area the next day too. You'll need to rake out the old mortar to at least a finger thickness depth or your new mortar will flake off. Now, this heavy use of water may cause you problems because your bricks are invariably covered in soot and tar which is quite likely to run and stain your pointing. I don't really know how you're going to get round this other than cleaning them well beforehand and work from the top down. Definitely clean as you go unless you're wanting to acid-wash the lime out of the brick pores.
Edit - just re-read it's stone you're working with, so you'll need to do a lot less wetting (unless it's sandstone, in which case all my brick comments probably apply).
For limecrete I'd essentially make mortar then add aggregate to it until I got to the right consistency/ratio. you're essentially looking for the aggregate packed solidly and mortar filling in the gaps but no more.
Post edited at 16:14