How to Calculate Wall Plaster – Ceme isnt & Sand

 

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 How to Calculate Wall Plaster – Cement & Sand

Plastering is an essential finishing work in construction that provides a smooth surface for walls and ceilings. To achieve a strong and durable plaster, correct calculation of cement and sand quantity is very important.

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* Step 1: Understand Plastering Mix

The most commonly used plaster mix is Cement : Sand = 1:4 or 1:6 (by volume).

• 1:4 mix → For internal walls, bathrooms, wet areas
• 1:6 mix → For outer walls, normal plastering

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* Step 2: Formula for Plaster Quantity

Plaster volume =Area of wall *Plaster thickness 

• Area of Wall = Length × Height
• Thickness = Convert mm into meters (e.g., 12 mm = 0.012 m)

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* Step 3: Add Wastage

Always add 30% extra for wastage and uneven surfaces.

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# Example Calculation

Given:

• Wall size = 10 m (length) × 3 m (height) = 30 m²
• Plaster thickness = 12 mm = 0.012 m
• Mix ratio = 1:4 (Cement:Sand)

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*. Step 1: Wet Volume of Plaster

Wet Volume= 30 * 0.012 = 0.36 m3

Add 30% wastage:

0.36 * 1.30 =0.468 m³

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 * Step 2: Dry Volume

Since dry volume = Wet volume × 1.33

0.468 * 1.33 = 0.622 m³

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 * Step 3: Cement & Sand Calculation

Mix = 1:4 → Total = 1 + 4 = 5 parts

• Cement = (1/5) × 0.622 = 0.124 m³ 
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• Sand = (4/5) × 0.622 = 0.498 m³

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*  Step 4: Convert Cement into Bags

1 m³ cement = 1440 kg
1 bag cement = 50 kg → 0.0347 m³

0.124 ÷ 0.0347 = 3.6 bags

👉 So, for 30 m² wall (12 mm thick, 1:4 mix):

• Cement = 4 bags (approx.)
• Sand = 0.50 m³ (before bulkage)

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# Bulkage of Sand – Importance in Construction

* What is Bulkage of Sand?

When sand contains moisture, a thin film of water forms around each particle. This traps air between particles and increases the apparent volume of sand.

👉 Example: 1 m³ of dry sand may look like 1.2 m³ moist sand (20% extra volume).
This phenomenon is called Bulkage of Sand.

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* Why is Bulkage Important?

1. Mix Proportion Error – If bulkage is ignored, the actual sand going into mortar or plaster will be less than required.
2. Weak Plaster/Concrete – Reduced sand → higher cement content → cracks and shrinkage.
3. Cost Effect – Wrong proportions increase material usage and cost.
4. Workability Issue – Bulked sand changes the consistency of mortar/concrete.

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* Bulkage Correction Formula

Corrected sand Volume =Calculated sand Volume 
  

Example:

• Required Sand = 0.50 m³
• Bulkage = 20%

0.50×1.20 = 0.60 m³

👉 So, 0.60 m³ moist sand is needed to get 0.50 m³ dry sand equivalent.

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* Practical Site Note

• Bulkage of sand generally varies between 15% – 30% depending on moisture.
• A field test can be done:
  • Fill a container with moist sand.
  • Pour water to remove air gaps.
  • The sand level drops – the difference shows bulkage %.

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* Key Takeaway

Bulkage of sand is a critical factor in plastering and concrete works.
Always adjust sand quantity by adding 20–30% (depending on site moisture) to maintain correct mix proportions and avoid strength problems.

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* Final Answer

To plaster a 10 m × 3 m wall (12 mm thick, 1:4 mix):

• Cement → 4 Bags
• Sand → 0.60 m³ (after bulkage adjustment)

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*  Key Notes

• For ceiling plaster, add extra 10% due to wastage.
• Always check sand quality (silt content < 8%).
• Use potable water for mixing.
• Adjust bulkage based on site moisture test.