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Repair Mortar Quantity Calculator — Significance & Field Notes

Estimating bags of polymer-modified mortar for spall and patch repair — where the datasheet rules, but the on-site arithmetic needs a sanity check.

Why this calc exists

Repair mortar is one of the few construction materials governed by the manufacturer's datasheet, not by an IS code. IS 456 says 'use materials suitable for the repair', and the rest is left to product TDS. That makes estimation harder — there's no Table 9 to fall back on, just bag yield claims (typically 1.8–2.2 kg/m²/mm).

The arithmetic is simple (area × thickness × wet density), but the field practice is messy: actual spall depths vary 2–4× across a single beam soffit, wastage runs 8–15 % (vs 3–5 % for new work), and primer/bonding-coat coverage is sometimes billed separately. The Repair Mortar Quantity calculator does the math with editable density and yield so you can match the actual product datasheet.

Code references (with provenance)

  • Surface preparation (ICRI / manufacturer guides) — All defective, cracked or delaminated concrete shall be cut out back to sound concrete.
  • IS 516 (Part 5/Sec 1):2018 — Rebound hammer / UPV survey for condition assessment prior to repair.
  • ICRI 210.1R — Guide for selecting and specifying concrete surface preparation (international, widely cited).
  • Product datasheet — binding for bag yield, open time, primer requirement.

Worked: 12 m² beam soffit, 30 mm average patch depth

Volume: 12 × 0.030 = 0.36 m³ wet mortar.

Wet density: 2,100 kg/m³ (typical polymer-modified). Mass = 0.36 × 2,100 = 756 kg.

Bag yield: 25 kg bag → 30.2 bags nominal; with 10 % wastage → 33 bags.

SBR bonding coat: coverage 0.20 kg/m² (typical) → 12 × 0.20 = 2.4 kg SBR.

Cost check: 33 × ₹450/bag + 2.4 × ₹250/kg = ₹14,850 + ₹600 = ₹15,450 for this repair.

Field notes (what trips people up)

  • The datasheet wins. Always enter the actual product's bag yield and wet density, not defaults. Two products with the same generic name can differ 30 % in coverage.
  • Spall depth variation is the real budget risk. Measure a representative grid (every 1–2 m²) and use the 75th percentile depth, not the average.
  • Primer / bonding bridge is sometimes a separate line item, sometimes included in the bag yield. Read the TDS carefully.
  • Curing matters more than for new concrete. Polymer-modified mortars need 3–7 days of moist curing, not the standard 7 for OPC. Skip the cure and you lose 30–50 % of the design strength at the bond line.

Worked example

Site: 45 m² of column-edge spalling (multiple floors, average 25 mm depth).

Output: volume 1.125 m³ · mass 2,363 kg · bags 95 · SBR primer 9 kg · total cost ≈ ₹48,000.

Verify in field: hammer-test the first 5 m² to confirm 25 mm is right; adjust before ordering the rest.

FAQ

Should I include wastage for repair work?

Yes — repair work generates more waste than new construction. 8–15 % depending on access (overhead work like soffits wastes more than accessible vertical faces).

Can I use OPC + sand instead of polymer-modified mortar?

For non-structural cosmetic patches, yes. For structural repairs where bond strength matters, use polymer-modified or epoxy-based systems. IS 456 Cl 13.4 says the repair must be 'at least as durable as the parent concrete'.

How long before the repair can be loaded?

Polymer-modified mortars typically reach design strength at 7 days, but full cure continues for 28 days. Traffic load after 3 days, structural load after 7 days — confirm with the TDS.

Related reading & tools

Indicative tool — not a substitute for engineering judgement. Results are computed from formulae and reference values cited to Indian Standards and other published codes as named on this page, using nominal default assumptions; clause and table references are given in good faith for study and preliminary checks. Always verify the current edition and amendments of any cited standard in the BIS catalogue before relying on it. Final mix proportions, structural checks and construction decisions must be confirmed by a qualified engineer against the project design brief, drawings and site conditions. ConcreteInfo accepts no liability for design, procurement or construction decisions taken on the basis of these tools. Code references & rights: Indian Standards are the property of the Bureau of Indian Standards (© BIS) — official PDFs at bis.gov.in. Shared in good faith as technical reference for the civil engineering fraternity — always verify against the official publication.