Mortar Calculator

Data Source & Methodology

All calculations for mortar mix proportions (ratios of cement, lime, and sand) are based on the specifications provided by **ASTM C270 / C270M-19a: Standard Specification for Mortar for Unit Masonry**. This standard defines the requirements for different mortar types (M, S, N, O) based on their properties and intended use.

Material volume and weight calculations use standard construction estimation formulas. Key assumptions include:

• Dry-to-Wet Conversion: A bulking/shrinkage factor of **1.33** is used. This means 1.33 m³ of dry materials are required to produce 1 m³ of wet, mixed mortar.
• Material Densities (approximate):
  • Portland Cement: $1500 \text{ kg/m³}$
  • Hydrated Lime: $640 \text{ kg/m³}$
  • Dry Building Sand: $1600 \text{ kg/m³}$

The Formulas Explained

The calculation is a multi-step process to determine the weight of each dry ingredient (cement, lime, sand) from your project's dimensions.

1. Calculate Total Wet Mortar Volume ($V_{wet}$)

First, we find the total volume of wet, mixed mortar your project requires.

For Rendering / Plastering:

$V_{wet} \text{ (m³)} = \text{Area (m²)} \times \text{Thickness (m)}$

For Brickwork / Blockwork:

We calculate the total volume of the wall and subtract the total volume of the bricks/blocks, leaving only the mortar volume.

$V_{wall} = L_{wall} \times H_{wall} \times D_{unit}$
$N_{units} = \left( \frac{L_{wall}}{L_{unit} + J} \right) \times \left( \frac{H_{wall}}{H_{unit} + J} \right)$
$V_{units} = N_{units} \times (L_{unit} \times H_{unit} \times D_{unit})$
$V_{wet} = V_{wall} - V_{units}$

Where $J$ is the joint thickness, and all unit dimensions are converted to meters.

2. Calculate Total Dry Mix Volume ($V_{dry}$)

We apply the dry-to-wet conversion factor (bulking factor) to find the total volume of dry, unmixed ingredients needed.

$V_{dry} = V_{wet} \times 1.33$

3. Calculate Material Weights ($W$)

Using the mortar mix ratio (e.g., 1:1:6 for Type N), we find the volume of each material and convert it to weight using its density ($\rho$).

$P_{total} = P_{cement} + P_{lime} + P_{sand}$
$W_{material} = \left( \frac{V_{dry} \times P_{material}}{P_{total}} \right) \times \rho_{material}$

4. Apply Wastage ($\%_{waste}$)

Finally, we add the specified wastage percentage to get the final amount you should purchase.

$W_{final} = W_{material} \times \left( 1 + \frac{\%_{waste}}{100} \right)$

Glossary of Variables

• Project Type: The type of masonry work (brickwork or rendering).
• Wall Length/Height (m): The overall dimensions of your wall.
• Unit Length/Height/Depth (mm): The dimensions of a single brick or block.
• Mortar Joint (mm): The thickness of the mortar gap between units.
• Area (m²): The total surface area to be rendered or plastered.
• Mortar Thickness (mm): The depth of the render or plaster coat.
• Mortar Mix Ratio: The proportional parts of Cement:Lime:Sand.
• Wastage (%): An allowance for material lost to spills, cuts, or over-application.
• Total Wet Mortar (m³): The final volume of mixed mortar required for the job.
• Material Required (kg): The final weight of cement, lime, and sand needed, including wastage.

How It Works: A Step-by-Step Example

Let's calculate the mortar for a garden wall using **Type N mortar**.

Inputs:

• Project Type: Brickwork
• Wall Length: 10 m
• Wall Height: 2 m
• Unit (Brick) Length: 215 mm (0.215 m)
• Unit (Brick) Height: 65 mm (0.065 m)
• Unit (Brick) Depth: 102.5 mm (0.1025 m)
• Mortar Joint: 10 mm (0.01 m)
• Mortar Type: Type N (Ratio 1:1:6)
• Wastage: 10%

Step 1: Calculate Wall & Unit Volumes

$V_{wall} = 10 \text{ m} \times 2 \text{ m} \times 0.1025 \text{ m} = 2.05 \text{ m³}$

$N_{units} = (10 / (0.215 + 0.01)) \times (2 / (0.065 + 0.01)) \approx 44.44 \times 26.67 \approx 1185 \text{ units}$

$V_{units} = 1185 \times (0.215 \times 0.065 \times 0.1025) \approx 1.694 \text{ m³}$

Step 2: Calculate Wet Mortar Volume ($V_{wet}$)

$V_{wet} = 2.05 - 1.694 = 0.356 \text{ m³}$

Step 3: Calculate Dry Mix Volume ($V_{dry}$)

$V_{dry} = 0.356 \times 1.33 = 0.473 \text{ m³}$

Step 4: Calculate Material Weights (Type N = 1:1:6, Total Parts = 8)

$W_{cement} = ( (0.473 \times 1) / 8 ) \times 1500 \text{ kg/m³} = 88.69 \text{ kg}$

$W_{lime} = ( (0.473 \times 1) / 8 ) \times 640 \text{ kg/m³} = 37.84 \text{ kg}$

$W_{sand} = ( (0.473 \times 6) / 8 ) \times 1600 \text{ kg/m³} = 567.6 \text{ kg}$

Step 5: Apply Wastage (10%)

Final Cement: $88.69 \times 1.10 = \mathbf{97.56 \text{ kg}}$ (e.g., 4 x 25kg bags)

Final Lime: $37.84 \times 1.10 = \mathbf{41.62 \text{ kg}}$

Final Sand: $567.6 \times 1.10 = \mathbf{624.36 \text{ kg}}$ (or 0.62 tonnes)

Frequently Asked Questions (FAQ)