15mm Thick plastering

Consider 100m²

Wet volume of concrete $=\frac{15}{1000}×100=1.5m³$

Add 30% for joint filling, Undulations, Wastage

$=\bigg(\frac{30}{100}×1.5\bigg)+1.5=1.95m³$

Add 20% for dry volume

$=\bigg(\frac{20}{100}×1.95\bigg)+1.95=1.95m³$

Cement Quantity $=\frac{2.34}{(1+4)}=0.468m³$

No. of bags = 13.48bags

Quantity of sand = 4×0.468 = 1.872 m³

Rate per $m³=\frac{24922.48}{100}=Rs.249.22/m²$