## CALCULATION OF MATERIALS FOR PLASTERING

To carry out the calculation of materials for plastering work, we must know the constituent of mortar. Mortar comprises of cement and sand. To calculate the quantity of these materials that will be needed for plastering work, we must get the dry volume of the cement mortar. This dry volume is gotten by multiplying the wet volume of mortar by a factor called the safety factor of mortar.

### 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 safety factor of mortar.

## 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.

### Example

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.

### Solution.

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