Find a masonry supply store. They can steer you in the right direction. You want "cement" not concrete. There are several formulations - basically soft to hard. You mix the cement with sand to make mortar. The cement used for modern hard fired brick is too hard for old bricks or stone masonry.
Back in the old days all they had was lime which made a very soft mortar. This actually allowed a little movement with seasons, weather, and settling. But because it is soft the weather and especially acid rain erodes is over time. After Portland cement was invented they started adding less or more of this to the lime to make it harder.
You'll need to pick the right type for what you are doing. I have a 110 year old barn and the mortar on the outside is failing on the east side. (The west side had been pointed at some time past since this sees the weather and afternoon sun.) While re-pointing this side I found that there was a slightly harder mortar on the outside to resist weathering, but the inside mortar was straight lime - so soft you can stick a screwdriver into it. So they were frugal and used pure lime on most of the job, and faced it with slightly harder (and more expensive) mortar with a little Portland cement added in.
Without going to the barn I think I used Type M but don't quote me. Hard enough to weather well but won't break the limestones in the foundation during extreme weather especially hard freezes.
I got a stone masonry book from the library that will tell you all you need. Good luck.
Re: 'Mortar' from scratch?
Posted: Wed Apr 05, 2017 6:32 pm
Thanks, 50 M C and JC
I found this if anyone is interested- explains the different types of hydrated lime, industry standards, strengths and recommended applications