Area to be plastered=100 m^2Thickness of plaster=12mm=(12/1000)m= 0.012mVolume of mortar required= 100 x 0.012= 1.20 m^3 Add 20% extra mortar for filling joint,depressions andwastage.

Volume of the mortar= [0.20 X 1.20]+ 1.20=1.44 m^3 [Wet Volume]

Increase further by One-third of the volume to get DryvolumeQuantity becomes= [(1/3) X 1.44]+ 1.44=1.92 m^3

Summation of proportion=1+4=5For 12mm plastering in 1:4 cement :sand mortar mix:

1)Cement required= 1.92/5= 0.384 cu. mNo. of bags of cement= 0.384/0.0347=11.06 bags 

>> 11 bags(say)Cement used =11 x 50= 550 kg

2)Sand required= [1.92 x (4/5)]= 1.536 cu. m

Important note:[Weight of 1 bag of cement= 50 kgCement should be always measured by weight to avoidvariation.

One 50 kg bag of cement weighs 1440 kg/cu. mVolume of 1 bag of cement= 50/1440=0.0347 cu. m ]

Therefore to convert Cu. m into No of bags of 50 kgcement,just divide the volume of cement by 0.0347

Brick work Dry volume

Volume of Dry Mortar = 35% of volume of Brickwork

Volume of Mortar required = 0.35 X 1 = 0.35 cu.m.

Cement required = 1/6 X 0.35 = 0.058 cu.m. = 1.67 Bags

Sand required = 5/6 X 0.35 = 0.292 cu.m.

Bricks required = 500 Nos.