Thor, or should that be Zeus?

[Tom J]

1/3 rd equal parts of Cement (52.5R), Sand (Sharp Sand, 0-2mm) and Basalt Stone (6-10mm). 20% Water volume based on Cement used (so in this case, 5 litres per 1 bag of 25kg each above).

...seems to be a lot of water.
In my work place we add circa 30 litres of water to 750kg of mix (all depends how wet is the sand).
This gives nice mix to form roof tiles. 10% water too much and mix is too wet and have to be dump - happens daily.
My point is to get correct amount of water - mix it well and we shall get strong cement.