Quoting a School Exterior Repaint: Areas, Litres and a Lump Sum
A contractor must quote for repainting the external cement-plaster walls of a single-storey primary school. The building is 24 m long and 12 m wide. The wall height is 3.6 m, and above it a continuous parapet band 0.9 m deep runs right round the same perimeter. Openings are 12 windows, each 1.5 m × 1.2 m, and 4 doors, each 1.0 m × 2.4 m; the contract says openings smaller than 0.5 m² are not deducted, and none of these are.
The existing coating is an old acrylic emulsion. About 30% of the wall area is flaking, with hairline cracks and some chalking; the rest is sound. The specification is one coat exterior primer and two coats exterior acrylic emulsion. Datasheet coverage is 10 m²/L for the primer and 8 m²/L per coat for the emulsion; the contractor allows 10% wastage. Primer costs ₹220 per litre and emulsion ₹310 per litre. Painter cost is ₹180 per hour at an output of 0.15 hour per m² per coat. Overheads and profit are 15% on material and labour combined. The client wants one lump-sum figure.
1. Calculate the net paintable area, showing every step and the deductions.
Read the worked answer
Perimeter. 2 × (24 + 12) = 72 m.
Main wall. 72 × 3.6 = 259.2 m².
Parapet band. The band runs round the same perimeter: 72 × 0.9 = 64.8 m². This is done on both faces in practice but the contract measures it once, so keep it as a single 64.8 m² item and state the assumption in the quotation.
Gross area. 259.2 + 64.8 = 324.0 m².
Deductions. Windows: 12 × (1.5 × 1.2) = 12 × 1.8 = 21.6 m². Doors: 4 × (1.0 × 2.4) = 9.6 m². Total deduction = 31.2 m². The contract says openings under 0.5 m² are not deducted and none are that small, so nothing is left undeducted.
Net paintable area. 324.0 − 31.2 = 292.8 m².
Note for the file: window and door reveals, sills and chajjas are not in this figure. They are real work and, if the client expects them painted, they must be measured and added - deducting the window opening while leaving the reveal unpriced is a common source of loss. Check the arithmetic once at tender stage and again on site; a 10 m² error here is small, but a 50 m² error on a larger building changes the margin.
2. Calculate the paint quantities with wastage and the material cost, then the labour hours and the final lump sum.
Read the worked answer
Primer. 292.8 ÷ 10 m²/L = 29.28 L. Add 10% wastage: 29.28 × 1.10 = 32.21 L. Cost 32.21 × ₹220 = ₹7,086.
Emulsion, per coat. 292.8 ÷ 8 = 36.6 L. Two coats = 73.2 L. Add 10%: 73.2 × 1.10 = 80.52 L. Cost 80.52 × ₹310 = ₹24,961.
Material total = 7,086 + 24,961 = ₹32,047. When buying, round up to full pack sizes (say 4 L cans): about 33 L primer and 81 L emulsion, i.e. 9 cans of primer and 21 cans of emulsion, and adjust the cost to what the supplier actually charges - the true wastage is often set by pack sizes, not by the 10% allowance.
Labour. Three coats × 0.15 h/m² = 0.45 h/m². 0.45 × 292.8 = 131.76 h. At ₹180/h = ₹23,717.
Subtotal = 32,047 + 23,717 = ₹55,764. Overheads and profit at 15% = ₹8,365. Lump sum = ₹64,129, quoted as about ₹64,000 at 219 ₹/m² for the painting items only.
Do not put the 30% repair work in this figure. 30% of 292.8 = 87.84 m² of scraping, wire brushing, crack raking and filling, spot priming and putty. Price it as a separate measured item (per m² of repair actually done, or a lump sum with a re-measure clause). If it is buried in the painting rate, the client sees one number and the contractor carries the risk of the defective area turning out to be 50%, not 30%.
3. What else must be added or excluded before this quotation can be issued safely?
Read the worked answer
Access. Work is up to 4.5 m (3.6 m wall plus 0.9 m band). That is beyond safe step-ladder reach for sustained work, so price scaffolding or a mobile tower with guardrails, plus erection and dismantling time. Note in the tender whether the contractor or the school supplies and permits it; it is usually a visible, arguable cost, so never hide it.
Surface preparation and moisture. Chalking must be removed or the new primer will not bond; test the plaster for friability and for rising damp (plastic sheet test or moisture meter), because painting over damp plaster guarantees blistering and early failure. State the moisture and dryness requirement as a condition of the contract and as a reason to postpone.
Weather. External emulsion needs a dry surface, air and substrate above about 10 °C and at least 3 °C above dew point, with rain-free time after application. Build a weather allowance and a start-date condition into the terms.
Exclusions to state in writing: scaffolding if not included, water and power supply, any structural crack repair, removal of fittings or boards, work outside normal hours, and repainting of areas rejected for damp. Also state the brand and sheen of the emulsion, the number of coats being priced, and that the area is based on the drawing dimensions subject to re-measurement. A lump sum without these clauses is a dispute waiting to happen.