It's gotta be wet cement on hardcore, a dry mix wouldn't work . And don't dot and dab as they rock over time I guess this can be mixed on a piece of woodor barrow if it's only an inch thick. Would u agree?
Yes 4:1 mix of sand/cement with water. Mixing it with a shovel on a large sheet of ply or an old sheet of timber is absolutely fine I have done it many times. If you have a large area to do though (other than pictured) it may make sense to get a mixer.