Jul 15, 2012· You want to make concrete, not mortar, so you should be using a concreting mix (sharp/concreting sand, not building/bricklayers/soft sand) and aggregate. The mould will give a smooth finish to the face of the slabs when you turn them out.
However, many people in India have doubts about quality of concrete / mortars when manufactured or artificial sand are used. Manufactured sand have been regularly used to make quality concrete for decades in India and abroad. Pune Mumbai expressway was completely built using artificial/manufactured sand. Issues with Manufactured Sand