What is plastering?
The process of covering the rough surfaces of walls/ceilings with plastic material to obtain an even, smooth, regular, and durable surface is called plastering.
The plastic material used depends upon the types of plaster required. The types of plaster generally used are,
- Lime plaster,
- Gypsum plaster,
- Cement plaster,
- Mud plaster etc.
In this article, let’s discuss how to calculate the quantity of cement and sand required for cement plastering.
Cement & Sand ratio for plastering
Cement mortar is used for plastering. Cement mortar is made by mixing cement and sand in a particular ratio. The common ratio for plastering is,
- 1:4 and
Here, one stands for the quantity of cement, and number 3,4, and 6 stands for the quantity of sand.
Depending upon the various place of application, different plaster ratios are used. Generally,
- For wall plastering, we use a 1:6 ratio.
- For ceiling plastering, we use a 1:4 ratio.
The reason behind this ratio selection is simple. A 1: 4 mortar ratio has a more sticky nature because we use only 4 parts of sand for one part of cement. In the other case, the 1:6 ratio is not as sticky when compared to the 1:4 ratio because it is more diluted. So, it is better to use a 1:4 ratio on ceiling plastering, because it has to stick against the pull of gravity.
What is the correct thickness of plastering?
The thickness of plastering is ranging from 6mm to 20mm. The whole thickness of plastering can be achieved either by one coat or by multiple coats.
Normally one coat is sufficient for ordinary buildings in dry or moderately wet climates. For important buildings (or) buildings in areas of heavy rainfall, multiple coats will be required.
- The thickness of plastering on the concrete face such as the ceiling should be 6 to 8mm.
- The thickness of plastering on the internal side of the wall should be 12 to 15mm.
- The thickness of plastering on the external side of the wall should be 15 to 20mm.
Refer IS 2402:1963, to know more about plastering.
Ok, now we know the basic things. Let’s learn how to calculate the materials required for plastering.
Plastering materials calculation
Let’s say, we are going to calculate the quantity of materials required to plaster a wall of 5m length and 3m height and the thickness of plastering is 12mm. The mortar is prepared in a 1:6 ratio.
Step 1: Volume of mortar required
Calculate the area you have planned to plaster and determine the volume of mortar required for plastering.
Plaster Area = Length x Width/Height
Plaster Area = 5m x 3m = 15 m2.
Volume of mortar req = Plaster Area x Thickness of plastering
Volume of mortar req = 15 m2 x 0.012 m = 0.18 m3. (1m = 1000mm)
Now, add an extra 30% of mortar for unevenness and fill up any joints in the surface.
Volume of mortar req = 0.18 x 1.3 = 0.234 m3.
Now, the arrived volume of the mortar is the wet volume. But we purchase materials in their dry state, so add an extra 25% of mortar to convert the wet volume into dry volume.
Dry volume of mortar req = 0.234 x 1.25 = 0.292 m3.
Step 2: Quantity of cement required
The ratio adopted here is 1:6. So, the cement proportion is 1, the sand proportion is 2, and the total proportion is 1+6 = 7.
Volume of cement required = 0.292 x (1/7) = 0.041 m3.
To convert into kg, multiply the above by the unit weight of cement which is 1440 kg/m3.
Quantity of cement required = 0.041 m3 x 1440 kg/m3 = 59.04 kg.
Number of cement bags required = Quantity of cement req / weight of one cement bag.
Generally, the weight of one cement bag is 50kg.
Number of cement bags req = 59.04/50 = 1.18 bags.
Step 3: Quantity of sand required
Volume of sand required = 0.292 x (6/7) = 0.250 m3.
To convert into cubic feet, multiply by 35.31.
Volume of sand required = 0.250 x 35.31 = 8.82 cft.
Thus, the volume of sand req = 0.250 m3 (or) 8.82 cft.
Excel sheet to calculate the quantity of materials for plastering
If you don’t want to do all the manual calculations (or) if you have any other dimensions you need to find, then download the excel sheet below to calculate the cement and sand required for plastering.
Hope you understand everything you need to know about plastering calculation. If you have any queries (or) if you find this article helpful, let us know in the comment section.