Plaster Bill for Twelve Rooms with an Extra-Thickness Claim
A panchayat building has 12 identical rooms, each 5.0 m x 4.0 m internally with a clear height of 3.2 m, 230 mm brick walls and a flat RCC roof. Every room has two doors of 1.0 m x 2.1 m and two windows of 1.5 m x 1.2 m. Internal plaster is specified as 12 mm cement mortar 1:4 on walls and ceiling. The contractor's running bill claims 78 m2 of 12 mm plaster and 8 bags of cement per room. The measurement book of the junior engineer records different figures. The contractor also claims an extra rate because 'about 15 m2 of plaster per room had to be made 18 mm thick to bring the wall plumb'. The store issue register shows 78 bags of cement and 11 m3 of sand issued for the plaster of all 12 rooms. The block engineer must settle the bill before the next instalment is released.
1. Measure the plaster area per room correctly, stating the deduction rule, and compare it with the contractor's claim.
Read the worked answer
Measurement of internal plaster, one room
- Perimeter of the room = 2 x (5.0 + 4.0) = 18.0 m.
- Wall area = 18.0 x 3.2 = 57.60 m2.
- Deductions for openings: the rule is that openings exceeding 0.5 m2 each are deducted, and openings of 0.5 m2 or less are neither deducted nor added.
- Door: 1.0 x 2.1 = 2.10 m2 each, above 0.5 m2, so deduct. Two doors = 4.20 m2.
- Window: 1.5 x 1.2 = 1.80 m2 each, above 0.5 m2, so deduct. Two windows = 3.60 m2.
- Total deduction = 7.80 m2.
- Net wall plaster = 57.60 - 7.80 = 49.80 m2.
- Ceiling = 5.0 x 4.0 = 20.00 m2 (no deduction).
- Total plaster per room = 69.80 m2.
Comparison with the claim
- Claimed: 78 m2 per room. Measured: 69.80 m2. Over-claim = 8.20 m2 per room, about 11.7 percent.
- Over 12 rooms that is 98.4 m2 of plaster claimed but not executed - roughly one and a half rooms of work.
- Note also what the claim omits: if the contractor had claimed only the wall area (57.60 minus 7.80 = 49.80 m2), that would be under-claiming because the ceiling is plastered too. The 78 figure looks as though openings were not deducted and the ceiling was then added roughly. Both errors point the same way - upward.
- The correct payable quantity for 12 rooms is 69.80 x 12 = 837.6 m2.
Judgement: the junior engineer's measurement book should be the basis, provided it shows the same step-by-step working and the deductions. Do not settle on a rounded figure without the calculation sheet attached to the bill.
2. Work out the cement and sand actually needed, and use the store issue figures to decide whether the bill or the site consumption is wrong.
Read the worked answer
Materials for 1:4 mortar, 12 mm thick, per room
- Wet mortar volume = 69.80 x 0.012 = 0.838 m3.
- Dry volume factor for mortar = 1.30, so dry volume = 0.838 x 1.30 = 1.089 m3.
- Cement = 1/5 of dry volume = 0.218 m3. At 1440 kg/m3 = 313.6 kg = 6.27 bags (50 kg each).
- With 5 percent wastage: about 6.6 bags.
- Sand = 4/5 of dry volume = 0.871 m3; with 5 percent wastage about 0.91 m3.
For 12 rooms
- Cement = 6.6 x 12 = 79 bags; sand = 0.91 x 12 = 10.9 m3.
Now compare the three sets of numbers
| Source | Cement for 12 rooms | Sand |
|---|---|---|
| Correct calculation | about 79 bags | about 10.9 m3 |
| Store issue register | 78 bags | 11 m3 |
| Contractor's bill (8 bags/room) | 96 bags | not stated |
- The store issue (78 bags, 11 m3) matches the calculation within 1 to 2 percent. Site consumption is normal; there is no evidence of leakage or theft.
- The bill's 8 bags per room and 78 m2 per room are both inflated. Billing 96 bags when 78 were drawn from store, for work that needed 79, is the finding to act on.
Conclusion: the store data corroborates the measurement, not the bill. Pass the measured quantity of 837.6 m2, and pay cement only as an integral part of the plaster rate - cement is not separately payable when the item is a composite plaster rate.
Note on the arithmetic: keep the working sheet with the bill, and state the dry-volume factor and wastage percentage used, so the contractor can see exactly where the difference arises.
3. How should the claim for 18 mm plaster on 15 m2 per room be handled?
Read the worked answer
The principle first
Plastering is measured and paid as area at a specified thickness. The rate already assumes the specified 12 mm. Extra thickness is not payable merely because it happened; it is payable only if it was ordered in writing by the engineer, or if the reason lies outside the contractor's control.
Test the claim against three questions
- Was the thicker plaster instructed? Check the site order book, the engineer's instructions and any variation order. If there is no written instruction, the claim fails at the first hurdle.
- Why was the wall out of plumb? The brickwork is the contractor's own work. If the masonry deviates beyond tolerance, extra plaster is the contractor's defect being hidden, not an extra item. Measure the walls with a plumb bob or spirit level on a straight edge at several points; a deviation of a few mm over a storey is within normal tolerance, anything larger is a workmanship failure.
- Was the extra thickness actually there? Measure with a depth probe or by a small patch at random points. A verbal claim of 15 m2 per room is not a measurement.
If, and only if, it was instructed
Quantify the extra: 15 m2 at 6 mm extra = 0.090 m3 wet mortar; with a 1.30 dry factor = 0.117 m3; cement = 1/5 = 0.0234 m3 = about 34 kg = 0.68 bags, plus about 0.09 m3 sand, plus the labour for one extra coat. Pay that as a rate-analysis-based extra, not as a percentage on the whole plaster item.
What to do in this case
- Record the plumb readings in the measurement book.
- If the deviation is the contractor's, reject the extra and note that the plaster is being paid at full 12 mm area already; if the deviation was pre-existing and the engineer directed 18 mm, approve only the measured area with the calculation above.
- Either way, record the reason in writing now. A claim left undecided becomes a dispute at final bill stage, when nobody remembers why the wall was crooked.