Concrete in the Detroit metropolitan area

Why concrete moves in the Detroit area

Cold is a genuine factor here and operates in the two ways it does anywhere with real winters: damage to the face of a surface from water freezing within it, and movement of a slab caused by the ground beneath it responding to sustained cold and available moisture. Both are ordinary and both are worth understanding, but neither is what makes this metro distinctive.

What is distinctive is age. A large quantity of the residential concrete in this region has been in the ground for a very long time by the standards of the rest of this platform, and material that old has been through enough cycles that its condition is a cumulative story rather than a single event. A homeowner looking for the one thing that caused a failure is often looking for something that does not exist; decades of ordinary exposure is the answer, and it is a legitimate one.

That has a clarifying effect on decisions. Where a slab has simply reached the end of a long service life — surface gone, edges breaking down, multiple cracks with deteriorated faces — restoring its elevation solves nothing, because elevation was never the problem. Conversely a much younger slab sitting in the wrong place with clean-edged cracks is a ground story and often correctable. The metro contains both situations in quantity, which is precisely why the era question comes first.

Ground conditions across this area vary and we will not characterise what is under any particular property, or generalise about the region's soils, because that is exactly the kind of claim that needs a source we do not have verified. Where drainage is concerned, though, the observable rule holds everywhere: water repeatedly delivered to one spot beside flatwork will eventually take fine material out from under it, and that is visible from a standing position on any lot.

How the area was built, and what that means for its concrete

The city core was platted for a way of living that did not assume a private car. Narrow lots, service alleys behind, detached garages at the rear of the plot, and public walks running the full frontage. The concrete that arrangement produces is different in kind from a modern driveway, and much of it is original.

The ring around the city grew in an intense and comparatively brief period, and it grew to a formula. Streets of houses on similar lots with similar setbacks and similar attached or side-facing garages went down over a handful of years, which means the flatwork on them is close to uniform in age, in specification and in what it has endured. That uniformity is the single most useful analytic fact about the suburban parts of this metro.

Beyond that ring, growth continued for decades on land that was farmed within living memory. Converting such land involves grading and filling, and ground so worked continues consolidating after houses are occupied. The result is a third population of flatwork: young, frequently intact, and sitting on ground still finding its level.

Those three populations demand three different first questions. For the oldest: has this reached the end of a long life. For the uniform ring: is this a cohort arriving at the same point together, and is my property's condition typical or an outlier. For the newest: is the concrete sound and merely displaced. Getting the population right is most of the diagnosis.

What comes up most in this metro

• Original city flatwork that has reached the end of a long service life
• Public walk panels displaced by established street trees
• Rear detached-garage aprons and service-alley approaches
• Post-war subdivision drives reaching the end of their lives across a whole street
• Attached-garage apron separation and settlement at the slab joint
• Ribbon and strip drives from an earlier era, and what to do with them
• Younger outer-ring flatwork displaced by ground still consolidating
• Drainage correction where roof water is delivered beside a drive or walk

Questions from Detroit homeowners