**STEP BY STEP TO CALCULATE THE NUMBERS OF BAGS OF PORTLAND CEMENT AND FINE AGGREGATE (Plastering Sand) THAT WILL BE NEEDED TO PLASTER THE WALLS OF A GIVEN PROJECT.**

If you have been finding it difficult to quantify the amount of cement and sand that are needed to complete a plaster of building using Mix Ratio.

we have ran down some steps which you will follow to achieve such result to avoid making mistakes.

For example, the above image is a One Bedroom flat needed to be plastered.

If the height from the Ground level to the ground floor of the building is 450mm [ that is 300mm + 150mm (ground floor concrete bed = 450mm)] and the height of the walls from the concrete bed to Ceiling is 3000mm.

**NOTE**: All the external walls are 3450mm from the ground level to ceiling and the internal walls are exactly 3000mm from the ground floor to the ceiling.

**1st STEP:**

**Sum up all the lengths of the walls: Starting from the external walls;**

5250mm + 2925mm + 3825mm + 2400mm + 4050mm + 2025mm + 1200mm + 1800mm + 2025mm + 8175mm + 8250mm + 1425mm

= 43,350mm.

**Spaces taken by Arches on the external walls.**

**At the entrance porch**, we have Arches of 5250mm length by 2400mm height and 1425mm length by 2400mm height.

**Total length of the Arches at the entrance porch.**

Length = 6675mm

Height = 2400mm

**At Kitchen Sit-out**, we have Arches of 2025mm length by 2400mm height and 1200mm length by 2400mm height.

Total length of the Arches at the Sit-out.

Length = 3225mm

Height = 2400mm

**Spaces taken by Windows on the external walls**.

**W1 -** This window is sized 900mm length by 1500mm height and they are total of 11 on the floor plan.

Total length of W1

= 900mm x 11 = 9900mm.

Height = 1500mm.

**W2 -** This window is sized 900mm length by 1200mm height and they are only 2 on the floor plan.

Total length of W2

= 900mm x 2 = 1800mm.

Height = 1200mm

**W3 -** These are Toilets windows whose size is 600mm by 600mm and are only 2 on the floor plan (One on the external wall while the other is on the internal wall).

Total length of W3

= 600mm x 2 = 1200mm

Also read: How to calculate the amount of cement, sand and granite for a concrete mix

**2nd STEP:**

Now, let us look into the internal walls;

After adding all the lengths of the internal walls and it gives us a total of 40,360mm.

**Spaces taken by Arches on the internal walls.**

**At the Lounge**, we have Arches of 3600mm length by 2400mm height and 1500mm length by 2400mm height.

Total length of the Arches at the Lounge

Length = 5100mm

Height = 2400mm

**At the Bedroom**, we have Arch of 1875mm length by 2400mm height.

**Spaces taken by Doors on the internal walls.**

**D1 - **This Door is sized 1200mm length by 2100mm height and it is only 1 on the floor plan.

**D2 -** This Door is sized 900mm length by 2100mm height and they are only 3 on the floor plan.

Total length of D2

= 900mm x 3 = 2700mm.

Height = 2100mm

**D3 -** These are Toilets, Store and Kitchen Sit-out Doors whose size is 750mm by 2100mm and they are total of 4 on the floor plan.

Total length of D3

= 750mm x 4 = 3000mm

**3rd STEP:**

Adding the total Length of the external walls and that of the internal walls which are 43,350mm and 40,360mm respectively.

So:

43,350mm + 40,360mm = 83,710mm and 3000mm height from the floor concrete bed.

**Total length of Arches on the plan.**

Length = 6675mm + 3225mm + 5100mm + 1875mm = 16,875mm.

Height = 2400mm.

Recall that the height from the ground level of the external walls to the concrete floor bed (ground floor) is 450mm and has a length of 43,350mm.

**Total length of Doors on the plan.**

Length = 1200mm + 2700mm + 3000mm = 6,900mm.

Height = 2,100mm.

**Total length of Windows on the plan.**

**For W1**, length and height = 9,900mm and 1500mm respectively.

**For W2**, length and height = 1800mm and 1200mm respectively.

**For W3**, length and height = 1200mm and 600mm respectively.

**4th Step:**

The image above shows a 225mm wall thickness in a section that has a plaster effect of thickness 25mm at both sides.

Plaster effect is always 25mm at both sides of every wall, some can go beyond it only if it's been used to correct any mistakes made by Bricklayers.

In this article, we will be making use of the plaster effect whose thickness is 25mm for our calculation to get the total number of bags of cement and Sand in Tons that will be needed to plaster IN and OUT of the walls of our proposed development.

**Now we are set to solving the Problem**

Adding the two thicknesses of the plaster effect on the wall together to get the total thickness.

That is 25mm + 25mm = 50mm= 0.05m = breath.

Calculating the constituents of plaster that were supposed to be on those Fenestrations, such as Arches, Doors and Windows.

**FOR ARCHES: from 3rd Step above**

Length = 16.875m

Height = 2.4m

Plaster breath = 0.05m

Volume of the plaster

= Length x Breath x Height

= 16.875m x 0.05m x 2.4m

= 2.025m³

Using Mix Ratio of 1:6 for the plaster,

We sum up the ratio of cement to that of Sand which is 1 + 6 = 7

Volume of cement in 2.025m³ of the plaster = 2.025m³ ÷ 7 = 0.29m³.

Volume of one bag of cement = 0.035m³.

So total number of bags of cement that were supposed to use to plaster the Arches "if they were walls"

= 0.29m³ ÷ 0.035m³

= 8.28 bags

Remember that the ratio 1:6 simply means to every one head pan of Portland Cement, you need 6 head pans of Sand.

Then volume of Sand in 2.025m³ of the plaster

= 0.29m³ x 6

= 1.74m³

Density of Sand = 1762kg/m³

Density = Mass ÷ Volume

Mass = Density x Volume

Mass = 1762kg/m³ x 1.74m³

= 3,065.88kg = 3.1 Tons

**FOR DOORS: from 3rd Step above**

Length = 6.9m

Height = 2.1m

Plaster breath = 0.05m

Volume of the plaster

= Length x Breath x Height

= 6.9m x 0.05m x 2.1m

= 0.725m³

Using Mix Ratio of 1:6

Volume of cement in 0.725m³ of the plaster = 0.725m³ ÷ 7 = 0.104m³

Volume of one bag of cement = 0.035m³

So total number of bags of cement that were supposed to use to plaster the Doors "if they were walls"

= 0.104m³ ÷ 0.035m³

= 2.96 bags = 3 bags approximately

To every one head pan of Portland Cement, you need 6 head pans of Sand.

Volume of Sand in 0.725m³ of the plaster

= 0.104m³ x 6

= 0.624m³

Density of Sand = 1762kg/m³

Density = Mass ÷ Volume

Mass = Density x Volume

Mass = 1762kg/m³ x 0.624m³

= 1,099.488kg = 1.1 Tons.

**FOR WINDOWS: from 3rd Step above**

Length of **W1** = 9.9m

Height of **W1** = 1.5m

Plaster breath = 0.05m

Volume of the plaster

= Length x Breath x Height

= 9.9m x 0.05m x 1.5m

= 0.743m³

Using Mix Ratio of 1:6

Volume of cement in 0.743m³ of the plaster = 0.743m³ ÷ 7 = 0.106m³

Volume of one bag of cement = 0.035m³

So, total number of bags of cement that were supposed to use to plaster the W1 "if they were walls"

= 0.106m³ ÷ 0.035m³

= 3.1 bags = 3 bags

To every one head pan of Portland Cement, you need 6 head pans of Sand.

Volume of Sand in 0.743m³ of the plaster

= 0.106m³ x 6

= 0.636m³

Density of Sand = 1762kg/m³

Density = Mass ÷ Volume

Mass = Density x Volume

Mass = 1762kg/m³ x 0.636m³

= 1,120.6kg = 1.12 Tons.

Length of **W2** = 1.8m

Height of **W2** = 1.2m

Plaster breath = 0.05m

Volume of the plaster

= Length x Breath x Height

= 1.8m x 0.05m x 1.2m

= 0.108m³

Using Mix Ratio of 1:6

Volume of cement in 0.108m³ of the plaster = 0.108m³ ÷ 7 = 0.015m³

Volume of one bag of cement = 0.035m³

Total number of bags of cement that were supposed to use to plaster the W2 "if they were walls"

= 0.015m³ ÷ 0.035m³

= 0.44 bag = about ½ bag of Cement.

To every one head pan of Portland Cement, you need 6 head pans of Sand.

Volume of Sand in 0.108m³ of the plaster

= 0.015m³ x 6

= 0.09m³

Density of Sand = 1762kg/m³

Density = Mass ÷ Volume

Mass = Density x Volume

Mass = 1762kg/m³ x 0.09m³

= 158.58kg = 0.16 Ton

Length of **W3** = 1.2m

Height of **W3** = 0.6m

Plaster breath = 0.05m

Volume of the plaster

= Length x Breath x Height

= 1.2m x 0.05m x 0.6m

= 0.036m³

Using Mix Ratio of 1:6

Volume of cement in 0.036m³ of the plaster = 0.036m³ ÷ 7 = 0.005m³

Volume of one bag of cement = 0.035m³

Total number of bags of cement that were supposed to be used to plaster the W3 "if they were walls"

= 0.005m³ ÷ 0.035m³

= 0.15 bag

To every one head pan of Portland Cement, you need 6 head pans of Sand.

Volume of Sand in 0.036m³ of the plaster

= 0.005m³ x 6

= 0.03m³

Density of Sand = 1762kg/m³

Density = Mass ÷ Volume

Mass = Density x Volume

Mass = 1762kg/m³ x 0.03m³

= 52.86kg = 0.05 Ton

Total number of bags of Portland Cement gotten in this 4th Step

= 8.28 +3 + 3 + 0.44 + 0.15

= **14.87 bags **

Total number of Tons of Plastering Sand gotten in this 4th Step

= 3.1 + 1.1 + 1.12 + 0.16 + 0.05

= **5.53 Tons**

**5th Step:**

Recall: The total length of all the walls from the concrete bed as calculated in 3rd Step above = 83,710mm = 83.71m = Length.

The Height of the walls = 3000mm = 3m.

Now, the volume of the plaster

= L x B x H

= 83.71m x 0.05m x 3m

= 12.56m³

From Mix Ratio 1:6

Volume of cement in 12.56m³ of the plaster = 12.56m³ ÷ 7 = 1.794m³

Volume of one bag of cement = 0.035m³

Number of bags of cement that will be on this 83.71m wall length

= 1.794m³ ÷ 0.035

= **51.25 bags**

To every one head pan of Portland Cement, you need 6 head pans of Sand.

Volume of Sand in 12.56m³ of the plaster

= 1.794m³ x 6

= 10.764m³

Density of Sand = 1762kg/m³

Density = Mass ÷ Volume

Mass = Density x Volume

Mass = 1762kg/m³ x 10.764m³

= 18966.168kg = 18.97 Tons.

**Also Recall that:** The total length of external walls whose height is 450mm from the Ground level to concrete floor bed = 43,350mm. = 43.35m = Length.

The Height of the walls = 450mm = 0.45m.

Now, the volume of the plaster that will be used for this very part:

= L x B x H

Remember that the breath here now is no longer 0.05m but 0.025m because we are now to plaster only one side of the wall.

= 43.35m x 0.025m x 0.45m

= 0.49m³

From Mix Ratio 1:6

Volume of cement in 0.49m³ of the plaster = 0.49m³ ÷ 7 = 0.07m³

Volume of one bag of cement = 0.035m³

Number of bags of cement

= 0.07m³ ÷ 0.035

= 1.99 bags, approximately 2 bags

To every one head pan of Portland Cement, you need 6 head pans of Sand.

Volume of Sand in 0.49m³ of the plaster

= 0.07m³ x 6

= 0.42m³

Density of Sand = 1762kg/m³

Density = Mass ÷ Volume

Mass = Density x Volume

Mass = 1762kg/m³ x 0.42m³

= 740.04kg = 0.74 Tons

**Total number of bags of Portland Cement gotten in this 5th Step **

= 51.25 +2

= 53.25 bags

**Total number of Tons of Plastering Sand gotten in this 5th Step**

= 18.97 + 0.74

= 19.71 Tons

**6th Step:**

(Total number of bags of cement in 5th Step) - (Total number of bags of cement in 4th Step)

= 53.25 Bags - 14.87 Bags

= 38.38 bags.

(Total quantity of Plastering Sand in 5th Step) - ( Total quantity of Plastering Sand in 4th Step)

= 19.71 Tons - 5.53 Tons

= 14.18 Tons.

**So we need 38.38 bags + (10% of 38.38 as wastage) to Plaster the walls of ONE Bedroom Flat.**

**That is 38.38 bags + 3.838 bags **

**= 42.2 Bags of Portland cement and about 15 Tons of Plastering Sand are needed for the wall to be plastered IN and OUT completely.**

**Note: The increase/decrease of the bags of cement depends on the Mix Ratio one chooses to use.**

Also read: Smooth Plastering (Step by Step Tutorial)

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