Why Concrete Cracks

Concrete cracks mainly because it shrinks as it cures, moves with changes in temperature and moisture, and sometimes carries loads it was not built for or sits on a base that has moved. Some hairline cracking is normal, but cracks that widen, offset, or let in water need attention. Bruck Construction builds and repairs concrete, and a site review can identify the likely cause of yours.

Why Does Concrete Shrink and Crack?

As concrete cures, it loses water and shrinks slightly. Curing is the chemical hardening process that continues while the concrete keeps enough moisture. Because the slab is held in place by the ground beneath it, that shrinkage builds tension, and the slab cracks where the tension is greatest. This is why fine cracks often appear in new slabs.

What Are Control Joints and Why Do They Matter?

Control joints are grooves cut into a slab so it cracks in a straight line at planned spots instead of randomly across the surface. Their spacing depends on slab size and thickness. A crack that runs along a joint line is usually doing what it was designed to do.

How Does the Base Affect Cracking?

A poorly compacted or washed-out base lets the slab settle unevenly, which causes cracks and sometimes leaves one side of a crack lower than the other. The base is the layer of compacted crushed stone under the slab, and its job is to provide firm, even support.

Why Do Cracks Often Start at Edges and Corners?

Edges and corners are where stress concentrates. A slab that is only supported on one side, or a corner that carries a turning vehicle, bends more than the middle of the slab does. Where a slab meets a building, post, or older pavement, it may also move on its own schedule, which opens a gap or a crack along that line.

How Do Heavy Loads Cause Cracks?

Concrete cracks when loads exceed what the slab was designed to carry, or when a slab is too thin for the traffic on it. Typical causes include:

• Heavy trucks or loaded equipment parked on a driveway or pad.
• Point loads from jacks, outriggers, or narrow wheels.
• Vehicles that turn sharply on a slab that was not designed for that use.
• Settlement under the slab that leaves part of it unsupported.

How Does Freeze-Thaw Damage Concrete?

Water that gets into the surface freezes and expands, which can break the top layer and widen existing cracks. Deicing salt can speed up this scaling, which is the flaking of the surface. Sealing and good drainage reduce how much water reaches the slab, which helps limit the damage.

When Should You Have Cracks Looked At?

Have cracks reviewed when they show signs of movement or water intrusion. Look for:

• Cracks wider than a hairline, or cracks that keep widening.
• Edges that lift, sink, or sit at different heights on either side.
• Water flowing through or pooling along a crack.
• Networks of cracks spreading across the slab, or pieces breaking loose.

Frequently asked questions

Are all concrete cracks a problem?

No. Thin, stable cracks are often cosmetic. Cracks that widen, offset, or let in water need a closer look.

Can cracks be filled?

Many cracks can be filled or sealed to keep water out. Filling treats the symptom, so the cause should be identified first, or the crack may return.

Does Bruck repair concrete?

Bruck Construction is a concrete contractor. We review cracking and explain the likely cause and options in a written estimate.

Concrete with cracks you are unsure about? Request a free estimate and we will explain what we see and what we recommend.