The crack that fills and stays fixed
A shrinkage crack, tight and level with both sides flush, is a good candidate for a simple repair. Filling or sealing it closes the gap so water and dirt stop working their way in, and because nothing underneath that crack is moving, the fix holds. That is most of what people call about.
This is the same kind of crack a control joint is meant to catch in the first place. Sometimes one opens outside the joint line anyway, still tight, still level, and filling that one is a straightforward job with a straightforward result.
The crack that comes back
A crack caused by movement under the slab is a different animal. Filling it covers the line for a while, but the section on one side is still settling, or the void under the edge is still there, and the concrete keeps responding to whatever is happening underneath it. The same crack, or one right next to it, tends to open again.
We see this most on driveways and garage floors where the base was never right to begin with: soft fill, organic soil that broke down, or water running under an edge and washing the fines out from under it.
Whether the crack is moving is the whole question, and it is the one thing worth settling before anyone buys a tube of filler. Our answer on structural cracks walks the checks.
Repairing the crack, or repairing what is under it
The two repairs are not the same size of job. Filling a tight, level crack is small work. The crack gets cleaned out, sealed, and the line stays where it is, closed instead of open. Cutting a failed section out and rebuilding the ground under it is a different order of work altogether, machine time and base work before any concrete goes back, and our cost page carries the numbers for both halves of that.
What separates them is how far down each one reaches. A sealant reaches the crack. It does not reach the subgrade, and on a slab that has moved, the subgrade is the part that failed. That is why we walk the slab and read the grade around it before we call a crack cosmetic, instead of pricing a repair off a description over the phone.
When a crack is worth repairing at all
Some cracks do not need anything done to them. A tight line at a control joint on a back patio is the joint doing the job it was cut for, and sealing it is a maintenance choice rather than a fix. If it does not bother you and water is not getting anywhere it matters, leaving it alone is a real answer, and we will tell you so.
What moves a crack onto the list is water and traffic. A crack open enough to hold water through a freeze and thaw winter at this elevation works itself wider every year, because water swells when it turns to ice and the crack is the one place it has room to push. A crack wide enough to catch a shovel edge, a mower wheel or a toe is worth closing for the same reason you would fix a loose step. Those are the ones where a repair earns what it costs you.
When patching buys real time, and when it does not
A shrinkage crack that gets filled stays fixed because the cause of it is already finished happening. A movement crack that gets patched buys you a season, maybe two, before the same forces open it again, sometimes wider.
If the crack traces back to a base we prepared, that is our problem to fix under the workmanship warranty in writing on your original estimate. Call before you decide which kind of crack you are looking at. We would rather walk it with you than have you patch the wrong thing.