Cement-sand and cement-lime-sand mortar grades, with 28-day compressive strength, cement consumption per cubic metre of wet mortar, and recommended use. Richer mixes (1:3) for plinth, pointing, and waterproofing; leaner mixes (1:6, 1:8) for general brickwork above plinth.
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Cement-Sand Mortar Grades
Strengths are 28-day cube tests on 1:3 sand cube (IS 2250)
Ratio Type Strength Cement / m³ Sand / m³ Use 1:3 MM 7.5 (rich) 7.5 N/mm² 440 kg / 8.8 bags 1.0 m³ (loose) Plinth, retaining walls, RCC pointing, water-retaining work, RR masonry below ground 1:4 MM 5.0 5.0 N/mm² 340 kg / 6.8 bags 1.0 m³ External plaster (1st coat), brickwork in load-bearing walls, pointing 1:5 MM 3.0 3.0 N/mm² 275 kg / 5.5 bags 1.0 m³ Internal plaster, brickwork in non-load-bearing walls 1:6 MM 2.0 2.0 N/mm² 230 kg / 4.6 bags 1.0 m³ Brickwork above plinth (most common), single-coat plaster, ceiling plaster 1:7 MM 1.5 1.5 N/mm² 200 kg / 4.0 bags 1.0 m³ Half-brick partitions, lean masonry 1:8 MM 1.0 (lean) 1.0 N/mm² 180 kg / 3.6 bags 1.0 m³ Filling, very low-strength masonry, compound walls
Cement-Lime-Sand Mortar (Compound)
Lime improves workability and reduces shrinkage — popular before 1960, still used in heritage work
Ratio Type Strength Cement / m³ Sand / m³ Use 1:1:6 Compound MM 5.0 5.0 N/mm² 230 kg 1.0 m³ + 0.16 m³ lime External plaster, exposed brickwork, restoration of old buildings 1:2:9 Compound MM 2.5 2.5 N/mm² 150 kg 1.0 m³ + 0.21 m³ lime Internal plaster, finer finish on plaster 0:1:3 (lime) Pure lime 0.7 N/mm² 0 1.0 m³ + 0.33 m³ lime Heritage/conservation only — not modern construction
Plaster Coat Thicknesses & Mixes
Ratio Type Strength Cement / m³ Sand / m³ Use 1:4 / 1:5 External plaster (12 mm) — — — Single coat, external face — sand-faced finish 1:6 Internal plaster (12 mm) — — — Single coat, internal face — smooth finish 1:6 Ceiling plaster (6 mm) — — — RCC slab soffit; thinner coat 1:3 + 1:4 Two-coat external (20 mm) — — — 12 mm rough coat + 8 mm finish — for severely exposed walls 1:5 Pointing (10 mm) — — — Re-pointing exposed brickwork joints
Notes
• Cement consumption per m³ of wet mortar = (1/(1+R)) × 1.30 × 1440 kg, where R = sand:cement ratio
• Wastage allowance: 15% for plaster, 5% for masonry mortar
• Always use the same brand of cement throughout one wall — different brands cause cracking
• Mortar must be used within 30 minutes of mixing (OPC) or 60 minutes (PPC) — never re-temper
• Sand should be sieved through 2.36 mm sieve for plaster, 4.75 mm for masonry mortar
• Add water gradually until 'flow' is right — over-watering kills strength
• For waterproof mortar, add 100 g/bag of integral waterproofing compound
• Do not use mortar richer than 1:3 — drying shrinkage causes cracks
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