Rate Estimate for a Brick Wall with Openings
A client asks for a rate estimate for a 230 mm brick wall, 10.0 m long and 3.0 m high, in cement mortar 1:6. The wall contains two window openings of 1.2 m × 1.5 m and one door opening of 1.0 m × 2.1 m; all dimensions are clear openings and no lintel is included in this item. Bricks are traditional 230 mm × 110 mm × 70 mm, laid with 10 mm joints. Site data: bricks Rs 8 each, cement Rs 420 per 50 kg bag, sand Rs 1,600 per m³, mason and helper Rs 650 per m³ of brickwork, scaffolding Rs 800 lump sum. The contractor allows 5% wastage on bricks and 10% on mortar materials. The client wants both the rate per m³ and the total amount, and asks whether the brick rate or the cement rate is the bigger risk to the budget.
1. Compute the net brickwork volume after deducting the openings, stating the deduction rule you applied.
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Gross volume = 10.0 × 3.0 × 0.23 = 6.90 m³.
Deduction rule. Under IS 1200 (Part 3), openings larger than 0.1 m² are deducted in full from brickwork; smaller ones are ignored. All three openings here are far larger than 0.1 m², so all are deducted.
- Windows: 2 × 1.2 × 1.5 × 0.23 = 0.828 m³
- Door: 1.0 × 2.1 × 0.23 = 0.483 m³
- Total deduction = 1.311 m³
Net brickwork = 6.90 − 1.311 = 5.589 m³, say 5.59 m³.
The thickness of 0.23 m is used, not 0.24 m, because the wall is one brick thick and the measurement is the actual wall thickness. Lintels, plaster and scaffolding are separate items and are not deducted or added here.
2. Compute the number of bricks and the cement and sand quantities, stating your assumptions and wastage.
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Bricks per m³. With 10 mm joints the nominal module is (0.23+0.01) × (0.11+0.01) × (0.07+0.01) = 0.24 × 0.12 × 0.08 = 0.002304 m³. So 1/0.002304 = 434 bricks per m³.
Bricks = 5.589 × 434 = 2425.6, say 2426. With 5% wastage: 2547 bricks.
Mortar. Actual brick volume = 2426 × 0.001771 = 4.296 m³. Wet mortar = 5.589 − 4.296 = 1.293 m³. Dry mortar = 1.293 × 1.33 = 1.72 m³.
For 1:6 mortar, dry volume 7 parts:
- Cement = (1/7) × 1.72 = 0.2457 m³ × 1440 kg/m³ = 354 kg = 7.08 bags; with 10% wastage = 7.8 bags.
- Sand = (6/7) × 1.72 = 1.474 m³; with 10% wastage = 1.62 m³.
Assumptions: bulk density of cement 1440 kg/m³, dry-to-wet mortar factor 1.33, and no frog filling allowance separately (it is covered by the 1.33 factor and wastage).
3. Build the rate per m³ and the total cost, and identify which single input most affects the rate - justify with a sensitivity check.
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Cost build-up
| Item | Quantity | Rate | Amount (Rs) |
|---|---|---|---|
| Bricks | 2547 | 8.00 | 20,376 |
| Cement | 7.8 bags | 420 | 3,276 |
| Sand | 1.62 m³ | 1,600 | 2,592 |
| Labour | 5.589 m³ | 650 | 3,633 |
| Scaffolding | lump sum | - | 800 |
| Total | 30,677 |
Rate per m³ = 30,677 / 5.589 = Rs 5,489/m³, say Rs 5,490/m³. Total = about Rs 30,680.
Sensitivity. Bricks are 20,376/30,677 = 66% of the cost. A 10% rise in the brick rate adds Rs 2,038, i.e. +6.6% on the total. A 10% rise in the cement rate adds only Rs 328, i.e. +1.1%. So the brick rate and brick wastage are the bigger budget risk - they deserve the firmest quotation and the tightest site control on breakage. The estimate excludes lintels, plaster, GST and centring, which should be listed as exclusions.