Laying patio - Smooth slabs not bonded

[fizzy]

Have some chinese metamorphasised limestone being laid. Apparently very strong so only 15-20mm thick and underside is very smooth (machined). Laid on full semi-dry mix but has not bonded at all. Believe this doesn't matter except at edges - all are free. Not sufficient depth to edge them in without looking ugly. Any suggestions other than putting wood all round or seeing if it sticks to a wetter mix and relaying edges? Wondered if an outdoor tile adhesive is a possibility?

[Tony McC]

Use a thinset mortar or a normal mortar that has been beefed-up with SBR or Ronafix. They won't bond to the semi-dry bed, which would not normally be a major issue on a patio, but is relevant at free edges, where there MUST be some way of preventing lateral movement.