Skip to main content

Methods of repairing cracks

Short answer

Repair methods depend on width: hairline (<0.3 mm) fill with cement slurry; small (0.3-1 mm) rake V-groove and fill with 1:3 mortar; medium (1-3 mm) epoxy injection; wide (>3 mm) stitching, jacketing or rebuild. For settlement, underpinning; for RCC, epoxy injection, plate bonding, jacketing.

Explain the methods of repairing (remedial methods for) different types of cracks in building.

Cracks are repaired by the method that suits their type, width and cause. The cause (such as settlement) should be removed first.

Repair by crack width

Crack widthRemedy
Hairline (< 0.3 mm)Fill with cement slurry or paint-grade filler; fresh plaster
Small (0.3-1.0 mm)Rake out, fill with cement-sand mortar (1:3) or polymer-modified mortar
Medium (1-3 mm)Epoxy injection or cement grout through packers
Wide (> 3 mm)Remove and rebuild, stitching with steel clamps, epoxy mortar, jacketing
Foundation settlementUnderpinning, grouting, soil improvement
RCC cracksEpoxy injection, grouting, jacketing, bonding steel plates
Roof cracksWaterproof treatment, expansion joints, sealants

Methods in brief

  1. Surface sealing: hairline cracks are filled with cement slurry or polymer-modified paste.
  2. Raking and filling: crack is widened into a V groove (10-20 mm), cleaned, and filled with cement-sand mortar 1:3 or epoxy mortar.
  3. Epoxy injection: low-viscosity epoxy is injected through packers fixed along the crack; used for structural cracks in RCC.
  4. Grouting: cement or chemical grout pumped into wide cracks and voids.
  5. Stitching: U-shaped metal clamps fixed across the crack and embedded in epoxy or mortar.
  6. Jacketing / section enlargement: extra concrete cover with new reinforcement on columns and beams.
  7. Bonding steel plates or FRP on the tension face.
  8. Underpinning or soil improvement for settlement cracks.
  9. Re-plastering with chicken mesh over joints between different materials.
  10. Expansion joints / sealants for thermal cracks.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Building Technology chapter 10 questions →