In message , doozer
writes

Final points: Don't try compacting the dry mix - it's a complete dead
loss. You just damage it while you lay the slabs and sets solid anyway
The two slabbed areas I built following the above method hold 5500
litre water tanks and they've not moved a mm. If I had to do it again I
would probably try blobs of cement.

If you rake the dry mix into ridges you can get a little bit of club
hammer and block of wood adjustment.

regards

--
Tim Lamb