The Richer Mortar Claim
A contract BOQ has an item for 230 mm brickwork in cement mortar 1:6, covering 12 cubic metres at a quoted rate of 5,850 rupees per cubic metre. The contract rate analysis used cement at 420 rupees per 50 kg bag and sand at 1,600 rupees per cubic metre. The rate carries 15 per cent overheads and profit. After the first floor slab, the site engineer tells the mason that the toilet block brickwork, 4 cubic metres of the measured quantity, must be done in CM 1:4 instead of 1:6 for damp resistance, and the work is executed that way. The contractor now claims extra for the richer mortar. The supervisor says the change was given orally on a Friday when the assistant engineer was on leave, and no variation order exists. The quantity surveyor has to settle the claim at the final bill stage.
1. Calculate the net extra payable for the 4 cubic metres of toilet block brickwork. State your assumptions and show the arithmetic.
Read the worked answer
Assumptions (standard rate-analysis values, to be confirmed against the contract analysis):
- Wet mortar per cubic metre of 230 mm brickwork with 10 mm joints: 0.25 cubic metres.
- Dry volume factor: 1.33, so dry mortar = 0.25 x 1.33 = 0.3325 cubic metres per cubic metre of brickwork.
- Cement bulk density: 1,440 kg per cubic metre; one bag = 50 kg.
Per cubic metre of brickwork:
- CM 1:6 - cement = 0.3325 / 7 = 0.0475 cubic metres = 68.4 kg = 1.368 bags; sand = 0.3325 x 6/7 = 0.2850 cubic metres.
- CM 1:4 - cement = 0.3325 / 5 = 0.0665 cubic metres = 95.8 kg = 1.915 bags; sand = 0.3325 x 4/5 = 0.2660 cubic metres.
- Difference per cubic metre: plus 0.547 bag of cement, minus 0.019 cubic metre of sand.
For 4 cubic metres:
- Extra cement = 0.547 x 4 = 2.19 bags, costing 2.19 x 420 = 920 rupees.
- Less sand saved = 0.019 x 4 = 0.076 cubic metre, worth 0.076 x 1,600 = 122 rupees.
- Net direct difference = 798 rupees.
- Add 15 per cent overheads and profit = 798 x 1.15 = 918 rupees.
Answer: about 918 rupees, say 920 rupees, subject to the contract rate analysis figures. If the analysis carries 5 per cent cement wastage, add roughly 46 rupees. Labour is treated as unchanged, since the mixing effort per bag is the same order.
2. Is the contractor entitled to be paid? Base your answer on the instruction and the contract procedure, not on the merits of the mortar.
Read the worked answer
The technical merit is not the issue. CM 1:4 in a toilet block is a reasonable requirement for damp resistance. The question is whether a valid instruction to change exists.
Procedure to apply:
- Authority. Only the engineer or a representative with written delegated power can vary the works. Check the delegation. A site engineer giving a verbal change on a Friday may have had no authority at all.
- Form. Most contracts require instructions in writing, or oral instructions confirmed in writing within a stated period, often seven days. No confirmation exists here, and the work was done without one.
- Notice. The contractor should have given notice of the intended claim before executing the changed work. Doing it silently and claiming at the final bill is the weakest possible position.
- Substance. If the drawing or specification always required 1:4 and only the BOQ description was wrong, the employer bears the correction as a BOQ error. If the richer mix was the contractor's own choice for convenience, no payment is due.
Practical conclusion. The entitlement is genuine in substance if the change was truly ordered and the work is of value to the employer, but it is procedurally weak. Recommend confirming the instruction retrospectively, in writing, signed by the engineer, with the date and quantity, and then valuing the change. Refusing a genuine change purely on paperwork invites a dispute the employer is likely to lose.
3. Set out the valuation method and the documents you would insist on before certifying the amount.
Read the worked answer
Valuation method. Do not negotiate a lump sum. Value the change exactly as the contract values any variation: build the difference between the 1:6 and 1:4 rate analyses using the same material rates, labour constants, wastage and the same 15 per cent overheads and profit that the original rate carried. Then apply the approved difference to the measured quantity only - 4 cubic metres, not the full 12. Confirm the mortar volume and dry factor actually used in the contract analysis rather than importing textbook values, because that is the basis the contractor priced against.
Documents required before certification:
- A variation order or written confirmation signed by the authorised engineer, dated and cross-referenced to the drawing.
- The revised drawing or specification clause that required CM 1:4.
- Joint measurement of the 4 cubic metres in the measurement book, recorded as a separate item, not merged into the 12 cubic metres.
- The approved rate analysis for both mixes, signed by the quantity surveyor.
- Delivery challans and bag counts for the cement actually consumed in that portion, checked against theoretical consumption.
- A site instruction register entry and dated photographs of the toilet block masonry before plastering.
Process lesson. Certify nothing on the strength of an oral instruction. If the instruction register had been maintained and the change confirmed within seven days, this claim would have been settled in a week instead of at final bill.