Updated November 11th, 2019
Cement mortar is the most commonly used building material for plastering.
The main ingredients of cement mortar are cement and sand. It’s prepared by mixing cement, sand, and water.
Before plastering a surface we first need to get the required volume of cement and sand.
To calculate the cement and sand volume, you need to calculate the required quantity of mortar for plastering.
In this post, I’ll show you how to calculate the required mortar quantity for plastering easily.
Easy Process of Cement Mortar Calculation For Plastering
Calculating cement mortar volume for plastering is easy. You just need to get the AREA of the plastering surface and the THICKNESS of plaster.
Getting Plastering Area
The area of a surface you’re going to plaster is the plastering area. Take the length and width of the surface and multiply both dimensions to get the area.
Suppose, you’re going to plaster in a wall surface which is 10 feet long and 10 feet width. So the area of the plastering surface is,
=10′ × 10′
=100 square feet.
But, when you’re going to plaster in a room, there should be windows, doors, and other wall openings.
To get the actual mortar volume, you need to get the actual plaster quantity. To get the actual plaster quantity you need to deduct all the openings from your calculated plastering surface area.
Getting The Thickness Of Plaster
Once you get the plastering surface area, you then need to get the thickness of the plaster to calculate the required mortar volume for plastering.
The thickness of the plaster depends on the surface condition. On RCC surface, ½ inch thick plaster is good. But on the brick surface, the plaster thickness can be ¾ inch to 1½ inch.
So, when calculating cement mortar for plastering you’ll need to carefully check the required thickness for the surface you’re going to plaster.
As default, the plaster thickness is assumed as ½ inch.
Cement Mortar Calculation Formula For Plastering
The formula of cement mortar calculation for plastering is simple. You just need to get the mortar volume.
Multiplying the thickness of plaster with the plastering area you’ll get the mortar volume.
If we see that in a mathematical term, we’ll find,
Cement mortar volume for plastering = The surface area × Thickness of plaster.
Let’s assume the surface area is 100 square feet and the thickness of the plaster is ½ inch.
So, the cement mortar volume is,
=100′ × ½″
= 4.17 cubic feet.
This is the wet volume of mortar. If you want to calculate cement and sand required for this mortar, you need to convert this wet volume of mortar into dry volume.
Calculating Dry Volume of Mortar
The formula for converting the wet volume of mortar into the dry volume is
= wet mortar volume × 1.3
= 4.17 × 1.3
= 5.42 cubic feet.
You can ask me what is the 1.30 I used to calculate the dry volume of mortar. I’ve talked about this before on the post on how to calculate the dry volume of mortar.
Once you know the dry volume of mortar, you can now calculate the mortar ingredients easily. But for this, you need to know the cement and sand ratio in the mortar.
The ratio of Cement And Sand in Mortar For Plastering
We normally use the 1:4 ratio of cement and sand in mortar for plastering. That means, one unit cement will be mixed with four units of sand to prepare mortar.
We know one bag cement of 50 kilograms contains 1.25 cubic feet of cement. For mixing mortar with one bag of cement, you’ll need (1.25 × 4) five cubic feet of sand.
As you now understand the mix ratio, you can calculate the required ingredients for any volume of mortar.
Let’s see how.
Calculating Mortar Ingredients
The dry volume of mortar we calculated above is 5.42 cubic feet.
The sum of the ratio is (1+4) = 5.
The volume of cement is,
= 1.08 cubic feet.
As one bag of cement is 1.25 cubic feet. So we require, (1.08÷1.25)= 0.86 bag.
The volume of sand is,
=4.33 cubic feet.
So, for 100 square feet area of plastering surface with ½″ thickness and 1:4 ratio, we’ll need,
- Cement – 0.86 bag
- Sand – 4.33 cubic feet.
A Quick Technique For Calculating Ingredients of Cement Mortar
For 100 square feet plastering surface, required cement is,
= 0.86 bag
So, for 1 one square feet is,
= 0.0086 bag. Say, 0.01 bag.
And, for 1 square feet plastering surface, the required sand volume is,
=4.33 ÷ 100
= 0.043 cubic feet.
For 1 square foot of plastering area,
- Cement=0.01 bag
- Sand = 0.043 cubic feet.
Whenever you want to get the cement quantity, you just need to multiply the plaster quantity with 0.01. And if you want to calculate the required sand volume for plastering just multiply the plaster quantity with 0.043.
Required cement bag for plaster is 0.01P bag.
Required sand volume is 0.043P cubic feet.
P is the quantity of plaster in square feet.
Cement mortar calculation for plastering is actually easy. You just need to get the area of the plastering surface and the thickness of the plaster.
Multiplying the area and the plaster thickness, you’ll get the required mortar volume.
If you want to calculate the required quantity of cement and sand, multiply the plastering area with 0.01 and 0.043 respectively.
Share your expertise
How do you calculate the required water quantity for mortar? Do you have any idea? Please share in the comments below…