Cracks in concrete are one of the most common complaints homeowners and building owners face in India. You paint your wall beautifully, and within months a hairline crack appears near the beam-column junction. Or your ground-floor slab develops a network of fine cracks that collect dust and look unsightly. The good news is that not every crack signals structural failure — but every crack needs to be addressed. Water, chlorides, and carbon dioxide will exploit even a 0.2 mm crack to reach the reinforcement and start corrosion.
This guide covers the full spectrum of crack repair for concrete walls and floors in the Indian construction context. I will walk you through how to identify the type of crack, select the right repair method, and execute it properly so the repair lasts.
Types of Cracks in Concrete
Before you repair anything, you need to understand what kind of crack you are dealing with. The wrong repair method for a given crack type will fail — often within months.
Hairline (Plastic Shrinkage) Cracks: These are very fine, shallow cracks, typically less than 0.3 mm wide. They form when the concrete surface dries too quickly during finishing — common in Indian summers when the temperature is above 35°C and the wind is strong. They are usually cosmetic but can allow moisture ingress over time. Repair method: surface sealer or brush-applied epoxy coating.
Structural Cracks: These cracks are wider than 0.3 mm, often extending through the full thickness of the member. They may be vertical, diagonal, or stepped (following the mortar joints in masonry). They are caused by overloading, foundation settlement, design errors, or inadequate reinforcement. If the crack is active (still moving), structural assessment by a civil engineer is mandatory. Repair method: epoxy injection for dormant structural cracks; flexible sealant or joint for active cracks.
Shrinkage Cracks: These occur when concrete loses moisture during curing and contracts. Restrained shrinkage creates tensile stresses that crack the concrete at regular intervals. Common in large floor slabs and long walls without adequate control joints. They typically appear within the first few weeks after casting. Repair method: routing and sealing with a flexible sealant, or epoxy injection if structural integrity is a concern.
Settlement Cracks: These result from differential movement of the foundation — one part of the building settles more than another. They are usually diagonal, wider at one end, and often accompanied by doors and windows that stick. Settlement cracks require geotechnical investigation before repair. Repair method: address the foundation issue first, then epoxy injection or stitching for the crack.
How to Assess a Crack
Assessment determines whether the crack is active or dormant, structural or cosmetic. Here is the practical approach used by site engineers.
Use a crack width gauge or a simple feeler gauge to measure the width at several points along the length. For monitoring movement, install a glass tell-tale — a small glass strip glued across the crack. If it cracks within 30 days, the crack is active. A more precise method is a mechanical crack monitor (demountable mechanical strain gauge) that records movement in two axes. Check for water leakage — if water flows through the crack under pressure, it is a through-crack and requires injection. Tap the concrete on either side of the crack with a hammer. A hollow sound indicates delamination or debonding of the concrete cover. And look for rust stains around the crack — brown staining means the reinforcement is already corroding and must be addressed.
In Indian practice, I recommend engaging a structural engineer for any crack wider than 1 mm, any crack accompanied by deflection, and any crack in a beam or column — regardless of width.
Epoxy Injection for Structural Cracks
Epoxy injection is the gold standard for repairing structural cracks in concrete. It restores the tensile strength of the concrete and seals the crack against moisture and chlorides. The process works for dormant cracks between 0.2 mm and 3 mm wide in walls, slabs, beams, and columns.
The procedure starts with surface preparation — clean the crack and the area around it, and seal the crack surface with a rapid-setting epoxy paste, leaving gaps at regular intervals for injection ports. The port spacing depends on crack width and resin viscosity: for a 0.5 mm crack, ports are placed 150–200 mm apart; for a 1 mm crack, 200–300 mm apart. Low-viscosity epoxy (100–500 cP) is injected at the lowest port using a manual or pneumatic injection gun. Injection continues until resin flows out of the adjacent port, at which point that port is capped and injection moves to the next one. The injection pressure is typically 2–5 kg/cm² for walls and 1–3 kg/cm² for slabs.
The injected epoxy cures in 24–48 hours at 25°C. After curing, the surface seal is ground off flush with the concrete surface. The repaired crack is stronger than the surrounding concrete in tension.
In India, epoxy injection costs Rs 250–500 per linear foot for walls and Rs 300–600 per linear foot for overhead slabs, including material and labour.
Routing and Sealing for Non-Structural Cracks
For non-structural cracks — typical shrinkage cracks in floor slabs and walls — routing and sealing is the most cost-effective method. It does not restore structural strength, but it effectively seals the crack against water and dirt ingress.
Using an angle grinder with a diamond blade, rout the crack to create a groove 6–12 mm wide and 6–12 mm deep. The width-to-depth ratio should be approximately 1:1. Clean the groove with compressed air or a stiff brush to remove all dust and debris. Apply a primer if specified by the sealant manufacturer. Fill the groove with a flexible sealant — polyurethane or silicone sealant for floors (needs abrasion resistance), or acrylic sealant for walls (paintable). Tool the sealant with a spatula to ensure contact with the groove walls and a smooth finish.
For outdoor slabs and terraces, use a self-leveling polyurethane sealant that flows into the groove and cures to a flexible, weather-resistant seal. For indoor floors, a sand-filled epoxy mortar works well — it matches the concrete appearance and withstands foot traffic.
Grouting for Wide Cracks
Cracks wider than 5 mm — often found in mass concrete foundations, retaining walls, and old structures — are best repaired by cementitious or chemical grouting.
Clean the crack by flushing with water at low pressure. If the crack passes through the full thickness and water leaks from the other side, inject a chemical grout (polyurethane resin) that reacts with water and expands to form a flexible seal. For dry or low-moisture wide cracks, use a cementitious grout mixed with a shrinkage-compensating additive. The grout is pumped under low pressure (1–3 kg/cm²) using a hand pump or a piston pump until it emerges from vent holes drilled at intervals along the crack.
For structural restoration of wide cracks, consider crack stitching — drilling holes across the crack at regular intervals, inserting U-shaped steel staples bonded with epoxy, and then grouting the crack. This restores both integrity and watertightness.
Surface Preparation and Material Selection
No matter which method you use, surface preparation determines how long the repair lasts. In Indian conditions, dust and moisture are the two biggest enemies of crack repair. Before applying any sealant, epoxy, or grout, ensure the crack interior is clean and dry (except for cementitious grouts, which require a damp surface). Use compressed air or a vacuum to remove all dust. If the concrete is carbonated (common in old buildings), treat it with a neutralising agent before applying epoxy.
Material selection rules of thumb: for structural repair, always use epoxy — cementitious grouts have negligible tensile strength. For flexible sealing of moving cracks, use polyurethane or silicone sealant with at least 25% movement capacity. For cosmetic repair of hairline cracks on interior walls, a paintable acrylic sealant or an elastomeric wall coating works well. For industrial floors subject to forklift traffic, use a high-compression-strength epoxy mortar that can withstand wheel loads.
Always check the shelf life of epoxy resins — expired resin will not cure properly. In the Indian summer heat, store epoxy in a cool, shaded area. Mixed epoxy has a pot life of 20–45 minutes at 35°C, so mix only what you can apply in that window.
Cost of Concrete Crack Repair in India
Here are realistic cost ranges for crack repair in the Indian market as of 2026:
Surface sealing of hairline cracks with brush-applied epoxy: Rs 30–60 per square foot. Routing and sealing with PU sealant: Rs 100–200 per linear foot. Epoxy injection (material + labour): Rs 250–600 per linear foot depending on crack width and accessibility. Cementitious grouting of wide cracks: Rs 150–300 per linear foot. Crack stitching with stainless steel staples: Rs 800–1,500 per stitch including drilling and epoxy bonding.
These costs vary by city — expect 10–15% higher in Mumbai and Bangalore compared to Delhi NCR, primarily due to labour rates.