Metro Detroit concrete lives or dies by frost, water and salt

Flat lake-plain clay: the ground under most Detroit slabs

Long before there were subdivisions here, the land from the Detroit River back toward the first low hills lay under glacial lakes. Those lakes left behind a broad, nearly level plain of fine silt and clay, the dense gray material many local diggers simply call blue clay. It is firm when it is dry and undisturbed, but it drains slowly, holds water for days after a storm, and turns soft and sticky when it stays wet. Farther north and west, especially across much of Oakland County, the plain gives way to rolling glacial till and pockets of sand and gravel, so the soil can change noticeably within a single township.

A concrete slab handles squeezing forces well and bending forces poorly. On uniform, well-drained support it will carry a loaded SUV for decades. Put that same slab over a patch of saturated clay or a loose trench backfill and every crossing bends it slightly, until a crack opens along the line where firm ground meets soft. Much of the cracking you see on neighborhood driveways follows exactly those hidden boundaries: the edge of an old sewer trench, the backfilled strip beside a basement wall, or a low corner where water sits.

Flat ground makes drainage its own challenge. On a hillside, water at least leaves in a hurry. On a level Detroit-area lot it has nowhere obvious to go, so it spreads out, soaks in beside the slab and pools against foundations. A contractor who plans the pitch of each surface, where downspouts and sump lines discharge, and how the new concrete sits relative to the lawn is solving the problem that shortens slab life more than any other here.

Frost heave, freeze-thaw and the brine off your tires

Southeast Michigan winters swing across the freezing mark again and again, and frost reaches well down into the soil during a hard cold stretch. Clay and silt are the soils most prone to frost heave: as the ground freezes, water is drawn upward and forms layers of ice that lift whatever sits above them. The lift is uneven, so one slab rises more than its neighbor, joints open, and a garage slab or stoop can sit higher in February than in June. Repeat that for enough seasons and sections stop settling back where they belong.

The surface fights its own battle. Water absorbed into the top of the concrete freezes and expands inside the pores, and many cycles of that loosen the paste until thin flakes pop off, a condition called scaling. Deeper, chunkier breakouts are called spalling. Road salt tracked in on cars makes both worse, which is why the roughest patches on many driveways sit in the tire tracks and on the first few feet inside the garage.

Three defenses carry most of the weight. Air-entrained concrete contains microscopic bubbles that give freezing water somewhere to go, and it is standard good practice for exterior flatwork in freezing climates, so it is fair to ask a contractor to confirm it in writing. A surface that was finished without extra water sprinkled on and without being overworked keeps a stronger top layer. And a penetrating sealer, renewed on schedule, keeps less brine from soaking in to begin with.

How to read a concrete quote before you sign it

Two quotes for the same driveway can describe very different pours. The details that decide how the slab ages mostly disappear under the concrete, so they are worth pinning down on paper while the forms are still just a plan.

What goes under the slab

Topsoil, roots and soft clay should come out, and crushed stone should go in and be compacted in layers with a vibrating plate or a roller. On slow-draining clay a thicker compacted stone layer both spreads the load and gives water a way out from under the concrete. Ask how deep the excavation will go and what happens if the crew hits a soft or wet spot.

How thick, and where

A common residential thickness is about four inches, with more planned for areas that will see a pickup, a trailer or a motorhome. Edges where tires roll on and off are often thickened. The quote should say what thickness is planned for each part of the job.

Joints and reinforcement

Concrete shrinks as it hardens and will crack somewhere; joints decide where. A typical rule of thumb places them no farther apart, in feet, than two to three times the slab thickness in inches, cut deep enough and early enough to do their job. Wire mesh, rebar or fibers help hold cracked pieces tight and level, but only if they sit up inside the slab rather than on the ground below it.

Curing, pitch and cleanup

Concrete hardens through a chemical reaction with its own mix water rather than by drying out, so ask how the surface will be cured on a hot day or protected on a cold night. Confirm the direction and amount of slope, away from the house and off the slab. And check whether breaking out and hauling away the old concrete is included, since that can be a large share of a replacement job.

Request an estimate visit

Send the address and a sentence about the job: a new pour, a replacement, or a slab that has started to heave, sink or flake. A reply comes back to set up a visit.

Six kinds of residential concrete work

Home concrete jobs around Metro Detroit tend to fall into a handful of types, and many projects mix two or three. Replacing a front driveway often brings a new walk to the porch. A backyard patio frequently needs steps off a deck or a side door. Stamping, integral color and exposed aggregate can dress up most of them, at the cost of more upkeep. Repair sits in a category of its own, because the first question is whether the existing slab is worth saving.

Details worth gathering before you ask for an estimate

None of these is required, and rough answers are fine, but each one shortens the first conversation and makes the visit more productive.

• The address, and whether a homeowners association reviews exterior changes on your street.
• What you want built or fixed, and about how big it is; pacing it off is accurate enough.
• What will park or sit on it: family cars, a work van, a boat, a camper or a hot tub.
• Whether old concrete, asphalt or brick pavers have to come out first.
• Where water goes in a heavy storm, including downspouts, sump pump lines and low spots.
• The finish you picture, from a plain broom texture to a stamped pattern or added color.
• How a ready-mix truck could get close, since alleys, fences and detached garages change the approach.

If the work reaches the public sidewalk or street, as a new driveway approach usually does, ask your city or township which permits and inspections apply, and ask the HOA about its own review. Requirements vary widely across the three counties, and learning them early keeps the schedule intact.

What happens after you reach out

Once a request arrives, the next step is an in-person look at the property. Standing in the driveway or backyard is when the job gets defined for real: soil and grade get a close look, the contractor notes where water runs and collects, studies how the old concrete failed if there is any, and works out how a truck and equipment can reach the spot. A job that looks like a simple swap in a photo sometimes needs a drainage change or deeper base work once someone is standing on it.

Next you should receive the estimate on paper. The helpful kind spells out the area, the thickness, the base, the reinforcement, the joint plan, the finish, the removal and hauling, and the drainage. Line those items up when comparing estimates, because two totals for the same yard frequently describe two different pieces of work.

Should you decide to proceed, the pour date bends to the forecast; wet spring weeks and the first hard freezes of fall are the usual reasons dates move. Afterward, expect to keep feet off the new surface for a few days and vehicles off it for longer. The contractor will give dates that fit the particular pour and the temperatures it cured in.

Where requests come from across Metro Detroit

Most requests come from the three big counties that make up the core of the metro. Each mixes early twentieth century city blocks, postwar inner-ring suburbs and newer subdivisions, and the ground and drainage can shift from one street to the next, so the visit tells more than the ZIP code ever will.

Metro Detroit concrete questions, answered plainly