How to calculate plaster for wall?

The following are the steps involved in calculating plastering quantities:
1. Calculate the total area of the wall to be plastered in square metres (m2).
2. Think about the plastering ratio and thickness.
3. Calculate the Total Plastering Volume
4. Calculate the volume of cement and sand for both coats separately.
5. Determine the total amount of cement and sand needed for plastering.

For the purposes of calculation, we will use the following values:

The width and height of the wall are 10m and 10m, respectively.
First plastering coat ratio (Cement:Sand = 1:5) with a thickness of 12mm.
the thickness of the secondary coat of plastering (Cement:Sand = 1:3) and the ratio of the secondary coat of plastering (Cement:Sand = 1:3)

Step 1: Calculate the Area of Plastering

Area = width x height = 10 x 10 = 100m²

Step 2: Find the Volume of Plastering 

Volume of First Coat = Area of Plastering x Thickness of Plastering

= 100m2 x 12mm (Convert mm to m)

= 100×0.012 = 1.2m3

Hence, Volume of First Coat of Plastering = 1.2m3

The volume of Second Coat = Area of Plastering x Thickness of Plastering

= 100m2 x 8mm (Convert mm to m)

= 100×0.008 = 0.8m3

Therefore Volume of Second coat of plastering = 0.8m3

Step 3: Finding the individual quantities of Cement and Sand.

First coat ratio = 1:5 (1 part of Cement and 5 parts of Sand)

Total parts = 1+5 = 6

Quantity of Cement required for First coat =

(Total Volume of first coat plastering  x No. of Parts of cement) ÷ Total Parts

= 1.2 x 1/6  = 0.2m³

Quantity of Sand required for First coat =

(Total Volume of first coat plastering x No. of parts of sand) ÷ Total Parts

= 0.8 x 5/ 6 = 1.0m³

Similarly for Second coat,

Second coat ratio = 1:3 (1 part of cement and 3 parts of sand)

Total parts = 1+3 =4

Quantity of Cement required for Second coat

= (Total Volume of second coat plastering  x No. of Parts of cement) ÷ Total Parts

= 0.8 x 1/4 = 0.2m³

Quantity of Sand required for Second coat

= (Total Volume of second coat plastering x No. of parts of sand)÷ Total Parts

= 0.8 x 3/4 = 0.6m³

Step 4: Finding the quantity of water required for plastering:

Amount of water to be added in mix depends upon the moisture content present in cement, sand & atmosphere.

Quantity of water = 20% of total dry material (Cement+Sand)
= 20% of (574+2560) = 0.2 x 3134 = 627 litres.