Peter Morrill wrote:

I have just finished a brick wall around my front garden. I have ordered
some natural sandstone copings, with wrought iron railings to go on top.
Could anyone please advise me on the best mortar mix (and any other
hints) to lay the sandstone on top of the brickwork. Being on a main
road with heavy pedestrian traffic, I want the copings to be secure.
Many thanks
Peter Morrill

Mmm. Pretty much any mix will probably do. I have laid bricks and stones
with wildly varyg mixes from 2:1 to 20:1 sand/cement.

The porosity goes down and brittleness goes up with more cement.

Adding hydrated lime reduces the brittleness and makes a really nice mortar.

Try 1:1:6 lime/cement/sand.

Or 3:1 sand/cement.