i have laid the 40 mm ones straight onto a screed type mix and bashed them down maybe 30 mm with the mallet
they were solid the next day,pointed with easipoint day after
LLL
As above but sett in with a 2.5lb lump hammer and a 10mm gap all pointed with GTFK 800 epoxy pointing. These setts were 50mm thick anything thinner and you could pour some SBR and cement mix in to your prepared bed before laying them for peace of mind.