Cement bags and sand for internal and external plaster — thickness presets 6–20 mm, ratios 1:3 to 1:6 per IS 1661 / IS 2250 practice.
Materials required
bags cement
Wet mortar volume = area × thickness. Dry ingredients volume = wet × 1.33 (standard allowance for voids in sand and bulking). Cement and sand volumes follow the selected ratio; one 50 kg cement bag = 0.0347 m³ (density 1440 kg/m³).
Thickness and ratio choices follow IS 1661 (cement plastering practice) and IS 2250 (masonry mortars); the dry factor and wastage are stated assumptions — adjust wastage for your site conditions.
Given: 100 m² internal wall, 12 mm, 1:4, 10% wastage.
Wet mortar = 100 × 0.012 = 1.2 m³ → dry = 1.2 × 1.33 = 1.596 m³
Cement = 1.596/5 = 0.319 m³ = 9.2 bags → with 10% wastage ≈ 10.1 bags
Sand = 1.596 × 4/5 = 1.28 m³ → with wastage ≈ 1.41 m³ (49.7 cft)
100 ft² = 9.29 m². Wet mortar = 0.111 m³, dry = 0.148 m³ → cement 0.0296 m³ = 0.85 bags without wastage — roughly 1 bag per 100 ft² at 12 mm in 1:4 (with 10% wastage).
External walls exposed to weather are commonly plastered 15–20 mm thick in 1:4 or 1:5. Richer 1:3 is used for exposed finishes and water-retaining surfaces; 1:6 suits internal economy work. Follow the project specification where it exists.
One part of wet mortar needs about 33% more dry ingredients: fine aggregate contains voids and bulks with moisture. The factor is a long-standing estimating convention, not an IS-code constant — which is why it is printed as an assumption on the result card.
Often used together with this calculator — pick the next step in your design or QA loop.
Deep dive: read the full significance guide — the code clauses, assumptions and site meaning behind these numbers.