Cracks in concrete are inevitable — but not all cracks are equal. Some are cosmetic and pose no structural risk. Others indicate active structural problems that require immediate attention. For building owners and facility managers, the challenge is knowing which cracks to monitor, which to repair, and which demand urgent professional evaluation. This guide explains the types of concrete cracks, when crack injection is the right repair method, and how to choose between epoxy and polyurethane injection.
Understanding Concrete Cracks
Concrete cracks for many reasons, and the cause determines whether the crack is a concern. The most common causes in commercial buildings include:
Shrinkage Cracks
As concrete cures, it loses moisture and shrinks. This shrinkage creates fine cracks, typically less than 0.01 inches wide, that appear within the first few months after construction. Shrinkage cracks are generally cosmetic and do not affect structural capacity. However, they can allow water infiltration if they occur in below-grade walls or exposed slabs.
Thermal Cracks
Temperature changes cause concrete to expand and contract. In Texas, where surface temperatures can swing 80°F or more between summer and winter, thermal movement creates cracks — particularly at restraint points where the concrete cannot move freely. Thermal cracks tend to open and close with temperature cycles.
Settlement Cracks
When the soil beneath a foundation settles unevenly, the resulting differential movement cracks the concrete. Settlement cracks are common in Texas due to the expansive clay soils found throughout much of the state. These cracks are often diagonal and may indicate ongoing foundation movement.
Structural Overload Cracks
When a concrete element is subjected to loads exceeding its design capacity, cracks form in predictable patterns. Flexural cracks appear on the tension face of beams and slabs (typically the bottom). Shear cracks appear as diagonal lines near beam supports. These cracks indicate that the structure is being stressed beyond its intended capacity and require engineering evaluation.
Corrosion-Induced Cracks
When reinforcing steel corrodes inside concrete, the expanding rust creates internal pressure that cracks the concrete from the inside out. Corrosion cracks typically run parallel to the reinforcing bars and are often accompanied by rust staining on the concrete surface. These cracks indicate active deterioration that will worsen without intervention.
When to Repair: Crack Injection Methods
Crack injection is the process of filling a concrete crack with a liquid material that either restores structural capacity (epoxy) or seals against water infiltration (polyurethane). The choice between the two depends on the crack type and repair objective.
Epoxy Crack Injection
Epoxy injection is used for structural crack repair. When cured, structural epoxy has a tensile strength of 7,000-10,000 psi — stronger than the concrete itself. Epoxy injection effectively welds the crack shut, restoring the concrete to its original monolithic condition and full load-transfer capacity across the crack plane.
Epoxy injection is appropriate when:
- The crack is structural (affecting load-carrying capacity)
- The crack is dormant (not actively moving)
- The concrete is dry or only slightly damp at the crack location
- The crack width is between 0.002 and 0.5 inches
- Restoring full structural capacity across the crack is required
Epoxy injection is not appropriate for cracks that are actively moving (thermal or settlement cracks that open and close), cracks with active water flow, or cracks wider than 0.5 inches.
Polyurethane Crack Injection
Polyurethane injection is used for water-stopping and sealing. Polyurethane resins react with water to form a flexible, closed-cell foam that seals the crack against water infiltration. Unlike rigid epoxy, cured polyurethane remains flexible and can accommodate minor crack movement.
Polyurethane injection is appropriate when:
- The primary goal is stopping water leaks
- The crack has active water flow
- The crack is expected to continue moving (thermal or settlement cracks)
- The crack is in a below-grade wall or foundation
- Structural capacity restoration is not required
When to Worry: Cracks That Need Immediate Attention
Contact a structural engineer immediately if you observe any of the following:
- Cracks wider than 1/4 inch: Wide cracks may indicate significant structural movement or overloading.
- Cracks that are growing: If a crack is getting longer, wider, or more numerous over time, the underlying cause is active and worsening.
- Diagonal cracks near beam or column supports: These may indicate shear failure, which can lead to sudden structural collapse.
- Cracks with vertical offset: When one side of a crack is higher than the other, it indicates differential settlement or structural displacement.
- Cracks accompanied by rust staining: Rust stains indicate corroding reinforcing steel, which will continue to deteriorate and weaken the structure. Our 5 signs your building needs repair guide covers additional warning indicators.
- Multiple parallel cracks along rebar lines: This pattern indicates widespread corrosion of reinforcing steel.
- Cracks in post-tensioned slabs: Any cracking in a PT slab should be evaluated, as it may indicate loss of prestress force. See our post-tensioning repair guide for more on PT-specific issues.
- Cracks after a loading event: New cracks that appear after adding heavy equipment, changing building use, or a seismic event require immediate evaluation.
Crack Injection Cost Ranges
Crack injection costs depend on the type of material, crack length and depth, access conditions, and project size:
- Epoxy crack injection: $15-30 per linear foot for typical structural cracks
- Polyurethane crack injection: $20-40 per linear foot for water-stopping applications
- Surface seal and injection ports: Included in per-foot pricing for most contractors
- Engineering evaluation: $500-2,000 for a structural assessment of cracking, depending on building size and complexity
For buildings with extensive cracking, a comprehensive repair plan developed by a structural engineer is more cost-effective than addressing cracks individually. The engineer can prioritize repairs based on structural significance and develop a phased approach that fits your budget. For detailed pricing across all repair types, see our structural concrete repair cost guide.
Monitoring Cracks Before Repair
For cracks that are not immediately dangerous but warrant observation, simple monitoring techniques can track whether the crack is stable or progressing:
- Crack monitors: Inexpensive plastic gauges that are epoxied across the crack to measure movement over time.
- Pencil marks and dates: Mark the end of each crack with a pencil line and date. If the crack extends past the mark, it is growing.
- Width measurements: Use a crack comparator card (available from ICRI) to measure and record crack widths at regular intervals.
- Photography: Take dated photos of cracks with a ruler for scale. Compare photos over time to detect changes.
Texas Structural Concrete provides crack injection, structural assessment, and concrete repair services for commercial buildings throughout Texas. Contact us at 661-733-7009 or request a free assessment to evaluate cracking in your structure.