Plastering is done on the walls to remove surface imperfections, maintain line level and alignment. In addition to that it also acts as a protective surface for external walls.** Cement** plaster, Gypsum plaster and Lime plaster are the commonly used plastering materials for house constructions.

**Cement** plaster is made by mixing cement and sand in the proportions required. Cement plaster is applied to both interior and exterior walls to give them a smooth surface.

## Recommended Cement Mortar ratio for Plastering

Mix Ratio of Mortar | General Usage Recommended |

1:3 | Very rich mortar mix. Not recommended for general usage at sites. Can act as a repair mortar with a waterproofing/bonding agent |

1:4 | For External Plaster and for ceiling plaster |

1:5 | Brickwork Mortar and for Internal plaster (If sand is not fine Fineness Modulas > 3) |

1:6 | For Internal Plaster (if fine sand is available) |

## How to Calculate Cement And Sand Required for Cement Plastering

To arrive at the quantities of Cement, Sand and Water required for Plastering work, we need to understand on what parameters do these quantities depend.

- Volume of Plaster required: Volume of Plaster can be determined by multiplying the area of plastering to be done and thickness of plaster (12 mm in this case)
- Mix Ratio of Plaster: Mix ratio mean the ratio of Volume of Cement to the Sand used in the mixture. Plaster of mix ratio 1:4 mean that it contains one part of cement and 4 parts of sand by volume. Since the amount of cement and sand changes with the change in the mix ratio, it is one of the most important factors in determining the quantities.

## Quantities of Cement, Sand and Water in Various Plaster Mix ratios

Area (Sqm) | Plaster thickness (mm) | Mix Ratio of Mortar | Cement (in Kgs) | Sand (In cft) | Water (in Kgs) |

10 | 12 | 1:3 | 49.37 | 3.77 | 44 |

10 | 12 | 1:4 | 39.29 | 3.99 | 44 |

10 | 12 | 1:5 | 32.54 | 4.14 | 44 |

10 | 12 | 1:6 | 27.80 | 4.24 | 44 |

Wastage of materials is not considered in the calculation. You can consider a wastage factor of 5% to the above calculation.

**Tip:** Ready Made plaster bags (40 kg) are also available in market. They are ready to use and just water needs to be added to the mixture.

## Method-1: DLBD method to Calculate Cement, Sand and Water required for Plaster (1:4)

For calculation purposes, lets assume that the area that needs to be plastered is 100 sqft (10 ft X 10 ft wall) and a Plaster of Mix ratio 1:4 (cement:sand) is used.

We shall use DLBD method (Dry Loose Bulk Density) in determining the ratios. This is the most accurate method as it accounts for the variations in the Loose Bulk Density. Loose bulk density might vary based on the location available materials.

### Step-1: Calculate the weight of Materials required using Bulk Densities

Plaster of 1:4 Cement : sand (Volume proportion)

Volume of 1 Bag of Cement (50 kg) = 36 litre or 0.036 cum (cement loose density as 1440 kgs/cum)

Volume of Sand required (using 1:4 proportion) = 0.036 x 4 = 0.144 x 1600 = 230 kgs (considering sand dry bulk density as 1600 kgs/cum.)

Usually around 20% of water by weight of the total dry material is mixed in the mixture to achieve the desired workability.

Water required = Weight of total dry material * 20% = (50+230) x 0.2 = 56 liter = 0.056 cum

*(Keep this handy to derive initial water requirement in any cement mortar)

### Step-2: Calculate the Volume of Wet Plaster Mix

Cement = 50 kgs , Sand = 230 kgs and Water = 56 kgs

Total weight of the mixture = 50+230+56 kgs = 336 kgs

Density of Cement sand mortar = 2200 kg/cum (Approximately)

**So, Amount of plaster mortar (1: 4) yielded with one Bag of cement (50 kgs) = 336/2200 = 0.153 cum**

### Step-3: Calculate Plaster Volume Required

Amount of plaster mortar required for plastering 100 sq.ft. (10 sq.mtr) area of 12 mm thickness

= 10 x 0.012 = 0.12 cum

**Thus to do 100 sq.ft.plaster (12mm thick) with 1:4 proportion, the individual material required are**

### Step-4: Calculate Materials Required for Plaster Volume

Cement needed would be = (50/0.153)x 0.12 = 39.21 kgs. or 0.784 bags

Sand needed would be = (230/0.153)x 0.12 = 180 kgs or 5 cft

Bulkage of Sand is not taken into account. A correction for bulkage has to be taken into account.

Water needed would be = (56/0.153) x 0.12 = 44 liters.

**Note:** Keep wastage allowance of 5% over and above arrived quantities.

## Method-2: Empirical Method To calculate Cement, Sand And Water for Plaster (1:4)

The empirical method is easiest way to calculate the quantities of materials required. Again considering the same parameters (i.e., Area – 100 sqft or 10 Sq meter and thickness 12mm

### Step-1: Calculate the dry volume of cement and Sand Mixture Required

Volume of plaster = Area X Thickness = 10 sq.m. X 0.012 = 0.12 cu.m.

The wet volume of the mixture is always less than the dry volume.

Dry volume of motor required for plastering = 1.27 X Wet volume of plaster = 1.27 X 0.12 = 0.1524 cu.m.

### Step-2: Calculate the Volume of Sand and Cement Required

The mix ratio of plaster mortar is 1:4, So the volumes of materials required would be

Cement required = 1/5 X 0.1524 = 0.03048 cu.m.

Sand required = 4/5 X 0.1524 = 0.12192 cu.m.

### Step-3: Get weights of Required Materials Using Densities

To get the weights of materials required in multiply it with its density

Cement required = 0.03048 cu.m. X 1440 kg/cu.m. =** 43.89 Kgs**

Since Sand is usually measured in cu.ft. = 0.12192 X 35.29 = **4.302**** cu.ft. or 195 kgs**

You can calculate the cement and Sand requirement for other Thickness of plaster and Mix ratio by just changing the numbers.

**Note:** Keep wastage allowance of 5% over and above arrived quantities.