Why is my concrete driveway cracking?

Why is my concrete driveway cracking?

Nearly every cracked driveway in Henderson County traces back to one of four things: clay swelling and shrinking under the slab, a base that washed out or never got compacted, water freezing in and under the concrete, or the slab shrinking as it cured with nowhere planned to give. Tree roots are the fifth, and they are mostly a downtown problem.

All four leave different marks, and you can get a long way toward telling them apart from your own porch. A crack that has been hairline and flat for fifteen years is a different animal from one that widened last spring and now catches your shoe.

What does the crack look like, and what does that tell me?

Three things matter more than length: how wide it is, whether the two sides sit at the same height, and whether it opens and closes with the seasons. Hairline, flat and stable points at curing. Wide and flat means the ground moved or settled evenly. One side higher than the other means the support under the slab is gone, or something is pushing up.

Worth doing before you call anybody:

• Drag a shoe across it. If your toe catches, there is a height difference, and height difference is never cosmetic.
• Look at the drive in low evening sun. A dip that disappears at noon shows up as a shadow at seven.
• Watch it the day after a hard rain. A crack that stains dark and stays wet longer than the slab around it is feeding water into the base.

Does the clay out on the East End and Zion Road really move a slab?

Yes, and it moves twice a year. The ridge ground on that side of town holds clay that takes on water through a wet spring, swells, then shrinks back through a dry August. A slab poured on it without a compacted gravel base rides that cycle, and after a few seasons the concrete gives somewhere.

Where it gives is predictable. The longest stretch of slab with no joint in it cracks first, usually across the width. Clay cracks wander rather than run straight and widen in a dry stretch. Worst in late summer, tighter in March, and you are watching clay.

Why do driveways toward the river settle instead of crack?

On the bottomland between downtown and the levee, and out toward Reed and Spottsville, the water table sits high in a wet spring. Moving water carries the fines out of a gravel base a little at a time and leaves a void. Concrete does not span a void for long. The section breaks and drops, and you get a step rather than a hairline.

The panel that goes first is almost always the one taking roof water. Find where the downspout nearest the drive lets out, then look at the slab three feet from it. A hollow, drummy sound underfoot is the void.

Does freeze and thaw matter here if we never get a deep freeze?

It matters more than a deep freeze would. Henderson gets a freeze most nights and a thaw most afternoons from December into March. Ground that freezes in November and stays frozen moves a slab once. Ground that freezes and thaws dozens of times works on it dozens of times, driving water deeper each time.

The apron at the street goes first, every time. Shallowest base, everything that runs off the road, and the salt. Winter is also when a small crack becomes a real one, because water freezing in it levers the sides apart.

Why did a driveway less than two years old crack?

Fresh concrete shrinks as it cures and keeps shrinking slowly for months afterward. Control joints are cut to give that shrinkage a planned place to go. Cut late, cut too shallow, or spaced too far apart, and the slab chooses its own line instead, often during the first winter. Those cracks are cosmetic as long as nothing underneath is moving.

A joint has to be cut about a quarter of the way through the slab, and on a four-inch drive the panels want to be around ten feet. One scratched across the surface with an edger is decoration. Cracks running parallel to the joints and a few feet off them are the tell.

Can a tree do this?

Roots crack concrete, and the older streets downtown are where it shows. A mature sycamore puts roots well past the spread of its canopy, and one that finds the damp edge under a slab thickens a little every year until the slab has to go somewhere. The giveaway is a crack with one side clearly lifted, running roughly toward the trunk.

Cutting the root is not always the answer. On a big tree it can be a bad trade.

How long does a concrete driveway last in Henderson?

A concrete driveway built the right way lasts decades here. Four to six inches of compacted base, a full four inches of air-entrained concrete, joints cut on time, and a sealer before the first winter. Hairline cracking along the way is normal. A thin builder-grade pour straight onto clay can look rough inside ten years.

Sealing is the cheapest concrete work you will ever buy, and the first winter is the one that counts.

Is this a repair or a replacement?

Stable hairline cracks get routed and sealed, $250 - $900. A flaking surface over sound concrete gets patched at $400 - $1,200, or resurfaced at $4 - $8 per sq ft if it is everywhere. Replacement earns its keep when large areas have broken into pieces, when sections sit at different heights across the whole drive, or when the base itself is gone. Removal of a typical two-car drive runs $1,200 - $2,800.

What decides it is whether the slab is still supported. A sound slab with an ugly top is a repair. A slab that has lost its base is a new pour, because a fresh surface over a failed base fails again the same way. The page on concrete repair and replacement covers what that visit looks at, and the ranges by job are on what concrete costs in Henderson.

What should I photograph before calling?

Five pictures answer most of what a crew would otherwise drive out to see. Take them in daylight and send the rough dimensions of the drive along with them.

1. The whole driveway from the street, with the apron in the frame.
2. The worst crack from directly above with a coin or a tape next to it for scale.
3. The same crack from a crouch at one end, low and down the line, so a height difference or a dip shows.
4. The downspout or ditch closest to the damage.
5. The edge of the slab where it meets dirt or grass, which shows how thick the concrete actually is.

If the drive is old enough that you do not know what is under it, say so on the phone. It is a normal answer and it changes what gets quoted.