Not every crack is a problem, and not every problem can be patched. Here is how we decide between a repair and a full replacement on Southern California driveways and patios.
Every concrete slab cracks. That is not a defect and it is not a sign that someone did the job badly — concrete shrinks as it cures, and shrinkage has to go somewhere. The purpose of control joints is to decide in advance where that cracking happens so it lands in a straight tooled line instead of wandering across the middle of your driveway.
The question worth asking is not whether your slab has cracks. It is what kind of cracks they are, and what is causing them.
Cracks that are usually fine
Hairline cracks, generally under about an eighth of an inch wide, with both sides sitting at the same height and no movement when you step across them, are almost always cosmetic shrinkage. They are common in the first year after a pour and typically stabilize.
Cracks that follow a control joint are working exactly as intended. That is the joint doing its job.
These can be cleaned and filled with a flexible sealant to keep water and debris out. The repair is inexpensive and the slab is structurally fine.
Cracks that signal a real problem
Vertical displacement is the clearest warning. If one side of the crack sits higher than the other, the ground beneath the slab is no longer supporting it evenly. That is a base failure, not a surface failure, and resurfacing over it will not last.
Wide cracks — a quarter inch or more — that continue to open over time indicate ongoing movement. So do cracks that radiate outward from a single point, which usually means a void has opened underneath.
Spalling, where the surface flakes and pops away exposing the aggregate, points to a finishing or freeze-thaw issue and tends to spread across the whole slab rather than staying local.
Pattern cracking that breaks the slab into many independent pieces means the concrete has effectively stopped acting as a slab. At that point each piece settles on its own and trip hazards multiply.
The honest replacement threshold
Our rule of thumb: if more than about a third of the slab is compromised, or if there is any vertical displacement, replacement is the better value. Patching a failing base is money spent twice, because the same movement that broke the original slab will break the patch.
This matters most on driveways. A driveway carries more weight than any other flatwork on the property, and it is usually the oldest concrete there. On homes across Montclair, Covina, and West Covina we regularly see driveways poured in the 1950s at barely three inches thick over uncompacted base. There is no meaningful repair for that — the slab has reached the end of its service life.
What proper replacement involves
Removing the old concrete is the easy part. What determines whether the new slab lasts is what happens next: regrading the base, compacting it in lifts, setting forms to a slope that moves water away from the structure, and placing rebar on chairs so the steel actually sits in the middle of the slab rather than lying on the dirt.
Control joints then get cut on a layout matched to the slab dimensions, usually within the first day, so the concrete cracks where you decided it should.
If you are unsure which category your cracks fall into, we will tell you honestly. Sometimes the answer is a sealant and a few hundred dollars, and we would rather say that than sell a pour you do not need.