How to calculate the quantity of materials in plaster?
Plastering is a crucial step in any construction project as it provides a smooth and even finish to walls and ceilings.
To calculate the quantity of cement and sand required for plastering, you will need to know the area of the wall or ceiling that needs to be plastered and the thickness of the plaster layer. You will also need to decide on the ratio of cement to sand that you want to use.
For wall plaster, the common ratio is 1:6, which means that for every 1 part cement, you will need 6 parts of sand. For roof plaster, the common ratio is 1:4. The thickness of plaster lies somewhere between 12mm to 15mm. Let’s take an example of a 100sqm roof area that need to be plastered with a thickness of 12mm. The ratio of cement to sand is assumed to be 1:4.
Example: Calculate the quantity of Cement, and Sand required for a 100 sqm Roof area. Thickness of Plaster is 12mm. Ratio of Cement to Sand is 1 : 4.
Once you have this information, you can use the following steps to calculate the quantity of cement and sand required:
Now we know;
Ratio of cement to sand = 1:4
Total ratio = 1+4 = 5
Thickness of plaster is 12mm = 12/1000 = 0.012 m
Total Volume of Plaster = Area of Roof x Thickness of
Plaster = 100 x 0.012 = 1.2 m3
To account for the fact that the plaster mixture will reduce its volume due to addition of water during the mixing process, hence you will need to multiply the total volume by a factor of 1.35 to get the “Dry volume”. i.e, the true volume of material needed to cast 1.2 m3 of wet volume of plaster.
Dry volume = wet volume x 1.35 = 1.2 x 1.35 = 1.62 m2
Quantity of Cement Required:
To calculate the volume of cement needed, you will need to use the following formula:
Volume of Cement = (Ratio of Cement / Total Ratio) x Dry Volume.
In our example, if the ratio of cement to sand is 1:4, the total ratio would be 5 (1 + 4 = 5).
Using these values in the formula, we get:
Volume of Cement = (1 / 5) x 1.62 = 0.324 m3
Quantity of Sand Required:
To calculate the volume of sand needed, you can use the following formula:
Volume of Sand = (Ratio of Sand / Total Ratio) x Dry Volume.
Using the same values as before, we get:
Volume of Sand = (4/ 5) x 1.62 = 1.296m3
Number of Cement Bags Required:
Finally, to calculate the number of cement bags needed, divide the volume of cement by the volume of one cement bag. Cement bags are usually sold in 50KG bags and the volume of each bag is 0.035m3,
Number of Cement Bags = Volume of Cement/Volume of 1 Bag [Volume of 1 Bag = 1.25 CFT or 0.035 cum]
Number of Cement Bags = 0.324/0.035 = 9.25 Bags (say 10 bags)
So in our example, we would need 9.25 bags of cement rounded up to 10 bags.