There is a saying in the trade: there are two kinds of concrete - concrete that has cracked, and concrete that is going to. That is not cynicism, it is chemistry. Concrete shrinks as the mix water leaves it, roughly a sixteenth of an inch over every ten feet. That movement has to be relieved somewhere.
What separates a well-built slab from a badly built one is not the absence of cracking. It is whether the cracking happened at a planned joint, below the surface, where nobody ever sees it.
Shrinkage cracks: normal, and usually harmless
These are hairline, often meandering, and appear in the first weeks. They are the slab relieving drying stress. If they are tight, with no vertical offset between the two sides, they are cosmetic. Sealing them keeps water out, which matters more than appearance.
Settlement cracks: the subgrade is talking
If one side of a crack sits lower than the other, the ground under the slab moved. That is a compaction, drainage or void problem, and patching the crack without addressing the cause will simply produce the same crack again a season later.
- Vertical offset between the two sides of the crack
- Cracks that widen measurably from year to year
- Panels that rock or click under foot traffic
- Water pooling near the crack after rain
Expansive clay: the Sacramento Valley factor
Large parts of the region - Elk Grove, Antelope, much of south and east county - sit on clay that swells when it takes on water and shrinks when it dries out. Our climate delivers exactly the cycle that maximizes that movement: saturated winters and long, bone-dry summers.
A slab poured on clay that was compacted dry, with no reinforcement and no joint plan, will telegraph that seasonal movement within a couple of years. The fixes are unglamorous: moisture-condition the subgrade, use real reinforcement on chairs, keep joint panels near square, and get the water away from the slab edges.
Structural cracks: get eyes on it
Wide cracks in a foundation, diagonal cracking at corners, cracks accompanied by doors that stop latching or drywall separating - those are not flatwork questions. They belong to a structural engineer, and any contractor who offers to patch them without a look at the structure is selling you something.
What to do about a crack you are worried about
- Photograph it with a coin or tape measure for scale
- Mark the ends with a pencil and date them - growth over months tells you more than width today
- Check where roof and surface water goes near that slab
- Call a contractor before the crack becomes a broken panel
If you want a second opinion on a crack in Sacramento concrete, call 877-889-1187 and describe what you are seeing. Half of these conversations end with us telling people their slab is fine.