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Crack Injection Quantity Calculator — Epoxy/PU Resin Significance

Estimating epoxy or PU resin, packers, and surface-seal putty for structural and non-structural crack injection — including the wastage that site practice usually underestimates.

Why this calc exists

Crack injection is small in volume but expensive per kg — epoxy resin runs ₹1,200–2,500/kg. Under-estimate the resin and you're 30 % over budget; over-estimate and you're returning opened bottles that have cured in the can. The dimensions are deceptively simple (length × width × depth) but the actual crack depth in a concrete element is rarely what you measure on the surface.

For structural cracks (active, structural, water-retaining structures), epoxy resin is the default — high tensile strength, bonds to dry concrete, fills voids as small as 0.1 mm. For moving or wet cracks (expansion joints, water tanks, basements), polyurethane is preferred because it remains flexible. The Crack Injection Quantity calculator takes crack dimensions, resin type, and packer spacing — outputs resin in kg, packers in number, and surface-seal putty in kg.

Code references (with provenance)

  • Repair practice (EN 1504 principles) — Repair materials must be at least as durable as the parent concrete.
  • IS 516 (Part 5/Sec 1):2018 — UPV for crack depth measurement (BS 1881-203 transit-time method).
  • ACI 224.1R — Causes, evaluation, and repair of cracks in concrete (international).
  • Product TDS — resin viscosity, working time, mixing ratio, bond strength.

Worked: 12 m of 1 mm-wide structural crack, 150 mm deep, epoxy injection

Crack volume: 12 × 0.001 × 0.150 = 0.0018 m³ = 1.8 L wet resin.

Resin density: 1,100 kg/m³ (typical low-viscosity epoxy). Mass = 1.8 × 1.1 = 1.98 kg.

Wastage: 25 % (over-pumping, surface spill, pot loss) → 2.5 kg resin.

Packers: spacing 200 mm (typical for 150 mm depth), 12 m / 0.2 = 60 ports × 1.3 (corner/end extra) = 78 packers.

Surface-seal putty: 5 mm thick × 50 mm wide along 12 m = 0.003 m³ = ~4.5 kg.

Total cost (epoxy at ₹2,000/kg): 2.5 × 2,000 + 78 × ₹35 + 4.5 × ₹150 = ₹5,000 + ₹2,730 + ₹675 = ₹8,405.

Field notes (what trips people up)

  • Crack depth is what surprises you. Surface 1 mm cracks often go 80–150 mm deep in a slab; in a beam, they may run full depth. Measure with UPV transit-time method or a scope camera before bidding.
  • Wider ≠ more resin. Most crack widths are 0.3–3 mm; doubling width doubles resin volume but adds little engineering benefit (you've already lost structural continuity past the resin bond strength).
  • Packer spacing depends on depth. Rule of thumb: spacing ≤ 1.5 × depth. For 100 mm crack: packers every 150 mm.
  • Pressure is the limiting factor. Too low and the resin doesn't reach the crack tip; too high and the concrete blows out. Start at 1 bar, ramp to 4–7 bar for epoxy.

Worked example

Site: 25 m of hairline cracks in a basement wall, 0.5 mm wide, 200 mm deep, water seepage.

Output: 2.5 L wet resin · 4.2 kg PU (water-reactive) · 150 packers · 8 kg putty · cost ≈ ₹18,000.

Note: PU resin volume calculation includes the chemical reaction expansion (~3×); adjust based on TDS.

FAQ

Epoxy or PU?

Epoxy for structural, dry cracks (high strength, brittle). PU for moving, wet cracks (flexible, water-reactive, expands 2–3×). Match resin to the crack behaviour.

How do I measure crack depth?

Non-destructive: UPV transit-time method per IS 516 (Part 5/Sec 1):2018 (BS 1881-203). Destructive: core through the crack and inspect. For most projects, UPV at three points along the crack gives a defensible average.

Can injected cracks be load-bearing again?

Epoxy-injected cracks typically restore 70–90 % of the original tensile capacity across the crack plane. Not a structural 'repair' in the strength-restoration sense, but adequate for water-tightness and most service conditions.

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. ACI references are copyrighted by the American Concrete Institute — official documents at concrete.org. BS/EN references are copyrighted by BSI and CEN — bsigroup.com. Shared in good faith as technical reference for the civil engineering fraternity — always verify against the official publication.