personally i wouldnt got less then 4inchs but thats just me.. i normally go 5inchs for my own stuff because the money i save on labour i beef up my quality. 3inch would prob be ok to be honest even tho i would never do that
so 80pound(40kg) bags what are they worth?? 1m3 of concrete approx 2300kg-2500kg.. so if u need 1.2m3 approx
maths
2300kg x 1.2= 2760kg
2760kg / 40kg = 69 bags
thats a rough quote on weight. obviously thats not allowing water weight. find out price per bag, then ring batch plant and get price for 1.2m3 and see the difference. if its only a $20-$30 difference then for less work and fuel it may be easier to get it batched
yeh and by chasing your tail thats what i mean, but if u piss it right up (make it wet as) u will be fine