Introduction

Cracks in concrete aren’t always a structural disaster, but they’re never something to ignore. For contractors, knowing how to properly inspect concrete cracks can mean the difference between a quick repair and a costly callback. This guide breaks down how to inspect concrete cracks with a methodical, real-world approach that helps identify the root cause.

Step 1: Document the Crack

Before you touch anything, start by documenting the crack:
– Photograph it from multiple angles, including close-up and wide shots.
– Measure the width using a crack gauge or calipers.
– Map the location on a sketch or drawing of the slab.
– Check the orientation.
Also ask:
– When was the concrete poured?
– When did the crack first appear?
– Has it grown over time?

Step 2: Identify the Crack Type

Knowing the type of crack helps narrow down the potential causes. Here’s a rundown of the most common types:

• Plastic Shrinkage Cracks: Appear within the first 24–48 hours after pouring. Usually shallow and random. Caused by rapid moisture loss.
• Settlement Cracks: Happen when the ground beneath the concrete settles unevenly.
• Drying Shrinkage Cracks: Occur days to months after curing. Caused by volume loss as concrete dries.
• Thermal Cracking: Seen in large pours or slabs exposed to temperature swings.
• Structural Cracks: Wide, deep, and continuous through the slab. Caused by load issues or foundation problems.
• Crazing or Map Cracking: A network of very fine, shallow surface cracks. Cosmetic, not structural.

Step 3: Analyze Crack Width, Depth, and Activity

– Width: Cracks less than 1/16 inch are often hairline. Wider than that? Pay attention.
– Depth: Use a probe or hammer-sounding method.
– Movement: Use crack monitors or tape marks to track changes over time.

Step 4: Evaluate Contributing Factors

• Subgrade Conditions: Was the base compacted? Signs of erosion or poor drainage?
• Reinforcement Issues: Check rebar placement with radar or cover meter.
• Joint Placement: Were control joints cut properly?
• Moisture Content: High water-cement ratios lead to shrinkage.
• Load and Use Patterns: Are there unexpected or heavy point loads?

Step 5: Determine the Root Cause

Using the clues gathered, decide which category the crack fits into. Keep in mind more than one cause may contribute.

Step 6: Recommend Solutions Based on Cause

Match your repair to the crack cause.

Final Thoughts

Every concrete crack tells a story. Don’t just patch it and hope. Look at the big picture, inspect methodically, and match your repair to the cause. A thorough inspection protects your reputation and helps your client avoid future issues.