Large cracks mean the small warning stage is over.

Large Cracks from Shifting or Water Pressure: diagnosed and explained.

Crack width is the single most useful number a homeowner can put on foundation damage. Hairlines are the structure whispering; a crack you can fit a coin or a finger into is the structure yielding. Large cracks form when the forces on the foundation, soil compressing and sinking away beneath it, or water pressure pushing against and under it, have moved enough material that the concrete or masonry could no longer bridge the difference. The shape tells you which force is winning. Wide diagonal or stair step cracks that taper point at differential settlement, one section of the home dropping while another holds. Long horizontal cracks in a stem or retaining wall point at lateral water and soil pressure. Cracks paired with visible offset, where one face sits proud of the other, mean the sections are displacing, not merely separating. Water usually has a hand in it either way: saturated soil is heavier and pushes harder, moving water erodes support from under footings, and in Southern California, Arizona, and Nevada the expansive clay adds its swell and shrink cycle on top. A large crack rarely appears overnight; it is the sum of seasons of smaller movement. But once cracks reach real width, the structure has lost some capacity, water has an open path in, and both problems compound, so this is a measure now rather than watch and wait symptom.

For the repair side of this, the foundation repair solutions page lists every method Dalinghaus installs, including the ones that fix problems other than large cracks from shifting or water pressure.