Confused by Concrete Calculations

[noseall]

1 cement, 2 sand and 4 gravel is not equal to 1 cement and 6 ballast.

The gravel has air gaps between the stones that the sand mostly fits into. The equivalent would be 5 ballast.

Generally, if the aggregates are separate, the ratios are...

4 parts (20mm ) gravel

2 parts sharp sand

1 cement

Add water to taste.

A cube of concrete takes over two tonne of gear i.e. two tonnes ballast, 13-14 x 25kg bags of cement and water.

 

[EasyGoingPat]

Thank you all for that advice. Lot to digest, and some is contradictory so I'll have to make a judgement call, which will in part inevitably be based on cost (i.e. no point in buying stuff I don't need).

(With reference to the area of the slab - yes, this slab is indeed adding to an existing area.)

Kind wishes - Patrick

 

[robinbanks]

some is contradictory

I didn't find any significant contradictions here