Concrete is unforgiving of poor preparation, and the failures show up years later when nobody is inclined to link them back to what happened before the pour.
Cracking, and which kind matters
Concrete shrinks as it cures and moves with temperature. Some cracking is essentially inevitable, which is why control joints exist — they encourage cracking to happen in a straight line where it was planned rather than randomly.
Fine cracks following control joints are doing what they were designed to do. Fine surface crazing is generally cosmetic.
What matters more: wide cracks, cracks where one side has lifted relative to the other, and cracking that is actively progressing. Those indicate movement in what is beneath rather than normal curing behaviour.
Eastern Washington: freeze-thaw
The dominant deterioration mechanism in Spokane, Yakima and the Tri-Cities.
Water enters small cracks and the surface pores. It freezes, expands, and widens what it entered. Next winter it does it again to a slightly larger opening. Over successive cycles, small defects become significant ones.
Spalling — where the surface flakes and breaks away — is the visible result, and it accelerates once started because the damaged surface holds more water.
De-icing salts make this considerably worse, which is worth knowing before using them routinely on a driveway you care about.
Concrete for this environment needs appropriate specification, and sealing helps by reducing water absorption. Both matter more here than west of the Cascades.
Western Washington: water and base
Freeze-thaw is a minor factor in the marine lowlands. What causes problems here is water and what is underneath.
Persistently saturated ground beneath a slab, poor drainage, and inadequate base preparation lead to settlement and cracking. Slow-draining soils and high rainfall — Thurston County especially — make base preparation and drainage the determining factors.
Moss and algae on concrete are a Western Washington constant and a genuine slip hazard on walkways and steps rather than merely an appearance issue.
What determines whether new work lasts
Base preparation. Properly compacted, adequately thick, correctly graded base. Invisible once poured and the single biggest determinant of longevity.
Drainage. Water should run off and away, not pool on the surface or collect underneath.
Thickness and reinforcement. Appropriate to the intended load. A driveway carrying vehicles is not a patio.
Control joints. Correctly spaced and cut at the right time, so cracking happens where intended.
Curing. Concrete gains strength through a chemical process needing moisture and time. Rushed or poorly cured concrete is weaker permanently, and this is where corners get cut because it is invisible.
Judging a quote
Ask about base preparation depth and material. Ask about thickness and any reinforcement. Ask about control joint spacing. Ask about the curing approach.
East of the Cascades, ask specifically what mix specification is being used for freeze-thaw conditions, and whether sealing is recommended.
A contractor who answers those clearly is describing a different job from one who quotes a price per area with no detail.
Repair or replace
Surface deterioration on otherwise sound concrete can sometimes be resurfaced. Structural cracking, significant settlement or widespread spalling generally means replacement, because the problem is beneath the surface.
Where settlement is involved, the cause needs addressing first. New concrete over the same unstable base does the same thing again.