Volume of plaster = area × thickness = 100 × (15 × 10‌–3) = 1.5 cu m. Increase mortar by 30 % therefore = 1.5 × 1.3 = 1.95 cu m. For volume of dry mortar, 25% increases = 1.25 × 1.95 = 2.4375 cu m. Now given proportion is 1:6 Hence, 1 part is of cement and 6 part is of sand so, Cement =(