CostBuildrCement and Sand Quantities for Plaster Work
Plastering consumes significant quantities of cement and sand over the course of a house project. Knowing the exact quantities per square foot for each mix ratio helps you plan purchases, control costs, and verify your contractor's material requisitions. This guide provides the formulas and ready-reference numbers.
Cement and Sand per Sq Ft by Ratio
For 12 mm thick plaster: at 1:3 ratio, cement = 0.013 bags/sq ft, sand = 0.032 cft/sq ft. At 1:4 ratio, cement = 0.0085 bags/sq ft, sand = 0.042 cft/sq ft. At 1:6 ratio, cement = 0.0057 bags/sq ft, sand = 0.043 cft/sq ft. These per-unit figures make it easy to multiply by any wall area.
For 20 mm thick plaster (commonly used for exterior base coat): multiply the 12 mm figures by 1.67. So at 1:4, cement = 0.014 bags/sq ft and sand = 0.070 cft/sq ft. For a 2,000 sq ft exterior wall: cement = 28 bags, sand = 140 cft.
Choosing the Right Plaster Ratio
1:3 is a rich mix used for exterior finish coats and ceiling soffits where crack resistance is paramount. It's the most expensive ratio—use it sparingly on surfaces that need it most. 1:4 is the all-purpose ratio suitable for interior walls, exterior base coats, and any wet-area wall (bathrooms, kitchens).
1:6 is an economy mix acceptable only for dry interior walls in non-critical areas (store rooms, servant quarters). It saves about 35% cement compared to 1:4 but is more prone to cracking if not cured properly. Never use 1:6 on exterior walls or in moisture-prone areas.
Ordering and Batch Planning
Calculate your total plaster area by measuring every wall (both sides) and all ceilings, then subtract openings. Group areas by plaster type: 1:3 finish coat areas, 1:4 standard areas, and 1:6 economy areas. Sum the cement and sand for each group to get your total order.
Order sand in one lot for the entire plastering phase—buying in bulk saves 10–15%. Cement should be purchased in batches of 1–2 weeks' supply to keep it fresh. A skilled mason plasters about 100–120 sq ft per day (12 mm coat), so plan your daily cement consumption: roughly 1 bag per mason per day for 1:4 ratio.
よくある質問
How many bags of cement for plastering a room?
A 12×14 ft room (4 walls + ceiling ≈ 688 sq ft of plaster area at 12 mm thick, 1:4 ratio) requires approximately 5.8 bags of cement and 29 cft of sand. Add 10% contingency: 7 bags and 32 cft.
Which is better for plaster: river sand or crush sand?
River sand (natural fine aggregate) is preferred for plaster because its rounded grains produce a smoother finish. Manufactured crush sand works but may leave a slightly rougher texture. Sieve sand through a fine mesh to remove oversized particles before use.
Can I add lime to plaster?
Yes, adding 10–15% lime by weight of cement to plaster improves workability, reduces cracking, and provides a self-healing quality for micro-cracks. It's a traditional practice that remains valuable, especially for exterior plaster.