Five and one is the accepted hand mix mate .To work out quantity of ballast needed -length x width x depth ie 4 m x 6 m x .1 =2.4 m2.The square meterrage is then times by 2.2 which is the bulk of loose quantity in weight = 5.28 tonnes of ballast .8 bags of cement to the ton =42 bags of cement .
Concrete mixers are 3m2 ,6m2 and 8m2
You pay a part load charge for anything that isn’t a full load .
Reinforce it mate either 10 mm or 12 will do ,40 odd quid for 2.4 m x 4.8 m
There ,been longing to put some of you messers in your place for ages ,have that .