**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.

### 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 =500m^{2}

Plastering thickness =2cm = 0.02m

Wet volume = 500 x 0.02 = 10m^{3}

Safety factor = 1.30

Dry volume of mortar = 10 x 1.30 = 13m^{3}

Mix ratio = 1:6, sum of ratio = 1+6 = 7

Cement qty = 1/7 x 13 =1.857m^{3}

But the volume of a 50kg bag of cement
= 0.035m^{3}

Therefore, cement qty = 1.857/0.035 = 53.5 ~ 54bags of cement

Sand qty = 6/7×13 = 11.142m^{3}

Density of sand = 1600kg/m^{3}

Mass of sand = 1600x 11.142 = 17827.2kg

But 1000kg = 1tone, therefore, 17827.2,1000 = 17.827 ~ 18tones