Concrete shrinks — that's the first crack
All concrete shrinks as it cures, about a sixteenth of an inch per ten feet, and it will crack somewhere to relieve that. Control joints — the grooves or saw cuts every 8 to 12 feet — are where it's supposed to crack, and a hairline crack in the bottom of a joint is the system working. Random cracks across a panel mean the joints were too far apart, cut too late, or the slab was restrained by something.
Heat: thermal movement
A Surprise driveway goes from 50 degrees at dawn to 150 at the surface in July, and it expands and contracts every day. Expansion joints against the house, the garage slab and the sidewalk let it move; without them the slab pushes against something and cracks or spalls at the edge. Slabs poured in the heat without curing shrink more, faster, and crack more — see our hot-weather guide.
Expansive clay: the heaving
The northwest Valley has pockets of expansive clay — Surprise Farms, parts of El Mirage, north Peoria, and scattered lots everywhere — that swell when wet and shrink when dry. A slab on clay lifts when the irrigation runs and the monsoon comes, drops during the dry months, and cracks along the movement. A slab that's lifted at one edge, with a crack that's higher on one side, is on clay. Prevention is over-excavating the clay and replacing it with compacted base, or moisture-conditioning it, before the pour.
Uncompacted fill: the settling
Most of the sunken driveways and patios we lift in Surprise are on fill the builder dumped and didn't compact — the soil settled over ten years, the slab followed, and the panel by the garage or the walkway by the house dropped an inch. Polyurethane foam lifting fixes the symptom; compacting the base in lifts before the pour prevents it.
Caliche: the hard layer
Caliche — the cemented calcium-carbonate layer a foot or two down across much of the West Valley — is actually good bearing once it's broken and compacted. The problem is when excavation stops at the caliche in some places and goes through it in others, leaving a slab on mixed support. We break it consistently and compact base over it.
Sulfates: the crumbling
Some Arizona soils and irrigation water carry sulfates that attack ordinary cement over years, crumbling the bottom of a slab and spalling the surface. Type II or Type V sulfate-resistant cement is the fix, and we specify it where the soil report or the neighborhood's history calls for it.
Roots, water and traffic
Tree roots lift walkways and driveway edges; leaking irrigation and downspouts dumping at a slab edge soften the base underneath; a car driveway parked on by a motorhome breaks. Each is a specific cause with a specific fix — root barriers, drainage, six-inch pads.
Which cracks matter
| What you see | What it means | What to do |
|---|---|---|
| Hairline crack in a control joint | Normal | Nothing |
| Fine spider-web cracks on the surface | Hot pour, dried too fast | Cosmetic; seal or resurface |
| Random crack, no height difference | Shrinkage or minor movement | Seal it; watch it |
| Crack with a lip — one side higher | Soil movement (clay or settlement) | Level or replace with proper base |
| Panel dropped at the garage or house | Settlement on uncompacted fill | Foam lifting |
| Surface crumbling or flaking | Sulfate attack or weak surface | Resurface or replace |
Common questions
My new driveway cracked in the first month. Is that normal?
A hairline crack in a control joint, yes. A random crack across a panel in the first month means the joints were cut too late or too far apart, or the pour dried too fast — and it's a workmanship conversation with whoever poured it.
Can a crack be repaired?
Sealed, yes, to keep water out. Made invisible, no — a repaired crack in gray concrete always shows. A resurfacing overlay hides hairlines; a moving crack comes back through anything.
How do I know if my soil is clay?
Cracks in the dirt during dry months that close after rain, a slab that's higher on one edge, doors that stick seasonally. We probe every site and tell you.
Does sealing prevent cracks?
No — sealing keeps water and stains out of the surface and protects color. Cracks are prevented by base, reinforcement, joints and curing.
Is foam lifting permanent?
Yes, on a slab that settled because the fill compacted. The foam doesn't wash out or shrink; the slab stays where we put it.
Related: Repair & leveling · Resurfacing · Hot-weather pours · Driveway cost