Concrete Cracks: Which Ones Are Cosmetic and Which Need Attention

Cosmetic cracks

Hairline shrinkage cracks. Concrete shrinks as it cures, and small cracks (under 1/16 inch) appear on most slabs within the first year. Random pattern, no offset between the two sides — these are normal and rarely structural.

Control joint cracks. Control joints (the sawn lines in your driveway or basement floor) are designed to direct cracks. A crack along the joint is the system working.

Pay-attention cracks

Cracks wider than 1/4 inch. Even if there's no offset, a wider crack lets water in. Sealing prevents freeze-thaw damage.

Active cracks. A crack that's changing shape or width with seasons or load is signaling movement. Worth monitoring; possibly worth investigation.

Diagonal cracks emanating from corners. Often from foundation settlement at a corner. The corner is the most flexible point on the foundation; movement shows up there first.

Take-action cracks

Stair-step cracks in masonry walls. Following the mortar joints in a diagonal stair pattern, especially with width over 1/4 inch and offset between sides. Often indicates differential settlement.

Horizontal cracks in basement walls. Pressure from outside (saturated soil, frost heave). Can indicate the wall is bowing inward.

Cracks with offset. One side of the crack is higher or lower than the other. Differential movement is happening.

Cracks that are leaking water. Even small ones — water under pressure finding a path is a real problem.

What this means for you

A photograph and a measurement (width, length) of any concerning crack gives you a baseline. A second photo in six months tells you whether it's growing.

What contractors should know

Customers want to know whether to worry or not. Confidently classifying their crack — with reasoning — builds trust and ends 90% of "is my foundation broken?" questions.

The part nobody can see later

Most of what decides how this holds up gets covered before the job is over. Once it is closed in, the only record of how it went in is the photos taken while it was still open.

Supervisr's Concrete and Masonry QA model works from common industry practice and the installation instructions that ship with the materials. It can evaluate concrete and masonry photos for control joint spacing, reinforcement placement, cure documentation, brick veneer anchoring, weep placement, and mortar joint tooling. Upload photos of control joint pattern and timing, rebar coverage and spacing, weep hole presence and spacing, brick tie spacing, mortar joint profile, and you'll get a documented evaluation back in minutes.

For a homeowner, that record is a straightforward way to understand what you paid for. For a contractor, it is the milestone documentation that stands behind a workmanship warranty years later, long after the crew has moved on to the next job.

About Supervisr

Supervisr is an AI quality-assurance platform for residential concrete and masonry work. It works from common industry practice and manufacturer installation instructions, and evaluates concrete and masonry photos against those published references.