Three Identical Flats: Primer and Emulsion Order
A painting contractor is quoting for three identical one-bedroom flats in a new block. Each flat has two rooms of 4.2 m × 3.6 m × 2.8 m high, one hall of 5.0 m × 4.0 m × 2.8 m, and a kitchen of 3.0 m × 2.4 m × 2.8 m. Walls and ceilings are to receive one coat of primer and two coats of emulsion. Deduct all openings: per flat, three doors of 0.9 m × 2.1 m and four windows of 1.2 m × 1.2 m. Primer coverage is 8 m² per litre per coat; emulsion coverage is 9 m² per litre per coat. The contractor adds 8% for wastage and rounding. The client will supply no material. The contractor can buy primer in 20-litre packs and emulsion in 20-litre packs. Labour and scaffolding are priced separately and are not part of this calculation.
1. Calculate the net paintable area per flat and for all three flats. Show the deductions clearly.
Read the worked answer
Per flat, calculate walls plus ceilings, then deduct openings.
Two identical rooms: perimeter = 2 × (4.2 + 3.6) = 15.6 m; wall area = 15.6 × 2.8 = 43.68 m²; ceiling = 4.2 × 3.6 = 15.12 m²; total per room = 58.80 m²; for two rooms = 117.60 m².
Hall: perimeter = 2 × (5.0 + 4.0) = 18.0 m; wall area = 18.0 × 2.8 = 50.40 m²; ceiling = 5.0 × 4.0 = 20.00 m²; total = 70.40 m².
Kitchen: perimeter = 2 × (3.0 + 2.4) = 10.8 m; wall area = 10.8 × 2.8 = 30.24 m²; ceiling = 3.0 × 2.4 = 7.20 m²; total = 37.44 m².
Gross per flat = 117.60 + 70.40 + 37.44 = 225.44 m². Openings: doors = 3 × 0.9 × 2.1 = 5.67 m²; windows = 4 × 1.2 × 1.2 = 5.76 m²; total deductions = 11.43 m². Net per flat = 225.44 − 11.43 = 214.01 m². For three flats = 214.01 × 3 = 642.03 m².
2. Calculate the primer and emulsion quantities after 8% wastage, and state the number of 20-litre packs to order.
Read the worked answer
Primer is one coat at 8 m²/L. Primer without wastage = 642.03 ÷ 8 = 80.25 L. Add 8%: 80.25 × 1.08 = 86.67 L. In 20-litre packs, 4 packs give 80 L, which is less than 86.67 L, so 5 packs (100 L) must be ordered.
Emulsion is two coats at 9 m²/L per coat. One coat = 642.03 ÷ 9 = 71.34 L. Two coats = 71.34 × 2 = 142.67 L. Add 8%: 142.67 × 1.08 = 154.08 L. In 20-litre packs, 7 packs give 140 L, which is insufficient; 8 packs give 160 L. Therefore order 5 × 20 L primer and 8 × 20 L emulsion.
The calculation assumes all areas receive the same system and that openings are deducted fully. If ceilings are to be a different product or colour, the quantities must be split. The 8% allowance covers normal loss but not major surface defects or extra coats.