Perfect Plaster – How to Calculate the Quantity of Material for Plaster

Why do you plaster your face with the façade of happiness?
– Anonymous

Well, that was a sad quote and one which uses peculiar words. For instance, Façade means “ a deceptive appearance” and plaster is a term that is used to describe “the thin mortar covering that is applied on the surface of the wall ceiling or wall.”

We can understand why the writer used the word Façade but why plaster? It somehow seems off right? Well true, but once you know why plaster is used you will understand why.

Calculating the amount of materials required

How much sand and cement do we need to plaster a wall? The answer is it depends on the surface area of the wall. Once you measure that, then you can use a set of formulas to calculate the specific quantity of sand and cement required. Yes, we are going into the realm of Math’s here.

Now for generic plastering, we use the ratio of 1:6 i.e. 1 part cement per 6 parts of sand. Before calculating the amount of quantity of materials that we require for plastering, however, we need to measure the surface area of the wall. After measuring that we have to calculate the dry volume of the plaster.

Once we do this we can move on to calculating the total required amount. We will need the following formulas to do this:

Dry volume of Mortar:
- Dry volume of mortar = Net Volume of mortar + volume of 25% of the total net volume
- Net volume of mortar = Initial volume + volume of water
- Initial Volume of mortar = Plaster Area x Plaster thickness in Meter
Number of cement Bags = [ (dry volume x Cement ratio)sum of ratio] / Volume of Cement Bag
Quantity of sand = [ (dry volume x sand ratio) /sum of ratio] x Density of sand

Now, these are rather easy formulas but for those who are not efficient in math’s, it might be a bit hard to understand. So we have given an example of how to calculate the quantities of materials required for plastering. Before we begin the process there are a few values that you need to know. They are:

The volume of water = 30% of the initial volume of mortar
The density of sand = 1602 kilogram per meter cubed
The volume of Cement Bag = 0.0035 Cubic meters
The weight of Sand per bag = 50 KG
The surface area of the wall = Let’s take 100 meter square for our case.

Now with these pieces of information gathered, we can move on to the calculation part.

1) Calculating the dry volume of Mortar

The dry volume of mortar is measured for determining the quantity of cement and sand for the formation of mortar for our masonry work.

The volume of Mortar = Plaster Area x Plaster thickness in Meter

Let’s assume that the plaster area is 100 meters square,

so we have got

Initial Volume of Mortar = 100 meter square x plaster thickness in meter
or : 100 Meter square x 0.012 Meters
or : 1.20 meter cubed

adding in 30% water to fill up joints and cover surface we have:

or : 1.20 Meter cubed + (30% of 1.20 meter cubed)
or : 1.20 Meter cubed + (30/100 x 1.20)
or : 1.20 Meter cubed + (0.3 x 1.20)
or : 1.20 + 0.36
or : 1.56 Meter cubed

Now as the water is mixed in the volume increases by 25 % of the total dry volume which leads to

aggregate dry volume of mortar = Net Volume of mortar + volume of 25% of the total net volume
or : 1.56 meter cubed + (25% of 1.56)
or : 1.56 meter cubed + (25/100 x 1.56)
or : 1.56 meter cubed + (0.25 x 1.56)
or : 1.56 meter cubed + 0.39
or: 1.95

So the total dry volume of mortar is 1.95 meters cubed.

2) Calculate the amount of Cement

Now that we have calculated this we can easily calculate the amount of cement required. To do this we can apply the following formula:

Number of cement bags= [ (dry volume x Cement ratio)sum of ratio] / Volume of Cement Bag

Let’s assume each cement bag has a volume of 0.035 meters cubed and has a weight of 50KG

or : [ (1.95 x Cement ratio) / sum of ratio)] / Volume of Cement Bag
or : [(1.95 x 1) / sum of ratio] / Volume of Cement Bag
or : [(1.95 x 1) / 6] / Volume of Cement Bag
or : [ (1.95 x 1) /6]/ 0.035
or : [1.95/6] / 0.035
or : 0.325/0.035
or : 9.285

So the number of cement bags required for plastering 100 meters cubed =9.285

Converting it into KG

We know that 1 bag of cement has 50 Kg of cement,

cement in weight = bags of cement x weight of each bag

or : 13.93 x 50

Or: 464. 25 Kgs of Cement

Hence to make a mortar to plaster an area of 100 meters square, you will need a total of 969.5 kilos of cement.

3) Calculate the amount of Sand

Mortar for plastering is composed of two materials i.e. cement and sand. To calculate the amount of sand required, we use a formula that is similar to the one used for calculating the amount of cement required. The formula is:

quantity of sand required = [ (dry volume x sand ratio) /sum of ratio] x Density of sand.

We know that density of sand = 1602 kg per meter cute

and Dry volume = 1.95 meters squared

So we have

Sand required = [(1.95 X sand ratio) /sum of ratio] x Density of sand.
or : [(1.95 x 5) sum of ratio] x Density of sand.
or : [(1.95 x 5)/6] x 1602
or : [(9.75)/6] x 1602
or : 1.625 x 1602
or : 2,603 kg

We know that 1 ton = 1000 Kg

So, 2,603 = 2.60 Ton

So this is how we calculate the amount of water, cement, and sand required for making a plastering mortar. But besides this, we should also know that there are different types of plastering as well.

Common width of Plastering

Plastering is used to increase the durability of the wall. It is also used for decorating the external surfaces and covering uneven surfaces as well. But that being said the different situation requires different width of plastering. Which are:

12 mm – used on the plain surface of the brick
15 mm – used on the rough side of 9 inches and 4.5 inches
18 mm – when turned into a neat cement slurry, it is used for making “dado” with the cement concrete flooring. Dado is the decorated lower part of a room that is below the waist height.
20 mm – used by applying two coats of 10 mm on the same side on a rough side of the wall for designing.

Conclusion,

Now you can either try and learn by experience or do math to know the amount of materials required for plastering a wall or a floor. Both of these options are valid ones but remember that by doing a little bit of math, you can save a lot of materials.

It is not easy to remember all of these formulas but you can save these formulas on the side and use them when needed. Also, you should be noted that the ratio of cement to sand used in this formula is meant for plastering mix on the interior of the house. If you want to make the plaster mortar for the use you should use the ratio of:

1:3 used to make repair mortar for waterproofing and bonding
1:4 for external and ceiling plaster
1:5 for brick mortar and Internal mortar if fine sand is not available.

One final note before we go, you can use both OPC and PPC cement for plastering. The use of OPC and PPC depends on your budget and your need for a set time. OPC cement is cheaper while PPC cement sets fast but is expensive

If you are curious about the difference between these two types of cement do check out the articles linked below.

And as always, thank you for reading till the end. Hope this was helpful for you. If you have any suggestions for us, do let us know them down in the comments below.