CALCULATION OF MATERIALS FOR PLASTERING
To carry out the calculation of
PLASTERING MORTAR SAFETY FACTOR
You will agree with me that sand has a void. The percentage of air voids compressibility of sand range from 20% to 27%. On this note, we consider the highest value which is 27%. The air void of cement is negligible due to the finesse nature of its particles. This means that, the volume of mortar after adding water decrees by 27%.
Therefore, the wet volume is increased by 27% to canter the shortage due to air voids of sand. It is also observed that about 3% of sand is wasted in the process due to the various place of mixing mortar. The total increment of the wet volume is now 27% + 3% = 30%. Now the volume of a cubic meter of mortar is unity (1). With the addition of the increments, we now have 1+ 0.30 = 1.30. This number is called
HOW TO CALCULATE THE DRY VOLUME OF PLASTERING MORTAR.
The dry volume of mortar is the factor on which the calculation of the materials depends. To get this factor, we first calculate the wet volume of mortar and thereafter, multiply the wet volume by the safety factor of mortar to get the dry volume of mortar.
Calculate the dry volume and materials quantity needed to plaster an area of wall measuring 50 x 10 with plastering thickness of 2cm. mix ratio is 1:6.
Area = 50×10 =500m2
Plastering thickness =2cm = 0.02m
Wet volume = 500 x 0.02 = 10m3
Safety factor = 1.30
Dry volume of mortar = 10 x 1.30 = 13m3
Mix ratio = 1:6, sum of ratio = 1+6 = 7
Cement qty = 1/7 x 13 =1.857m3
But the volume of a 50kg bag of cement = 0.035m3
Therefore, cement qty = 1.857/0.035 = 53.5 ~ 54bags of cement
Sand qty = 6/7×13 = 11.142m3
Density of sand = 1600kg/m3
Mass of sand = 1600x 11.142 = 17827.2kg
But 1000kg = 1tone, therefore, 17827.2,1000 = 17.827 ~ 18tones