You want your whole property to look sharp and stay safe, and that includes the sidewalk, driveway and patio. Concrete is the workhorse surface for American homes, but it causes trouble in two opposite directions: it can sink, and it can rise. We’ve been diagnosing both across the Denver metro since 1988, and the first question worth answering is the same one you’re probably asking. Which way is my slab moving, and how bad is it?

When you have a sunken slab of concrete or a cracked slab of sidewalk, it creates an eyesore and a hazard for anyone on your property. Concrete problems don’t heal on their own. The movement continues until the cause gets addressed, so a little diagnosis now saves real money later.

Heave or Settlement? How to Tell the Difference

Rising concrete (heave) and sinking concrete (settlement) can look surprisingly similar at a glance, since both leave a tripping lip between two slabs. So which slab actually moved? Here’s how we sort it out in the field:

  • Follow the edges. Sight along the slab toward a fixed reference like your foundation, garage floor or porch stoop. A settled slab drops below its original pour line, often leaving a gap or a dirt line visible on the foundation. A heaved slab climbs above it.
  • Read the crack pattern. Settlement cracks show up where the slab lost support, and the section past the crack tips downward. Heave tends to produce a peak, with the slab tilting up toward a high point over a root or a pocket of swollen soil.
  • Watch the timing. Heave in Colorado is usually seasonal. Our expansive clay swells after wet spells and lifts slabs, then relaxes as the soil dries out. Settlement is more of a one-way trip: the slab drops and stays down.
  • Look for a culprit. A tree within about 15 feet suggests roots. A downspout dumping at a slab corner points to washout and settlement underneath.

Measuring the Movement

You don’t need surveying equipment to track a moving slab. Lay a straight board or a 4-foot level across the joint and measure the gap with a tape measure. Write down the number, the date and the recent weather, then check again monthly. A slab that shifts with the seasons and comes back is being pushed by moisture in the soil. A slab that keeps dropping is settling over a growing void. Photos taken from the same spot help too, especially where a dirt line on the foundation marks the original height.

Why Concrete Rises

There are a few different causes of rising concrete, and one of them is roots. Snaking, bulging roots work their way under concrete and push it up over time, causing cracks, misplaced slabs and other headaches. The other big driver is soil. Certain fill soils like clay absorb far more water than other dirt and substrate, and clay dominates the ground along the Front Range. If the fill under your concrete was mixed or compacted improperly, sections can swell at different rates and shove the slab out of position.

What You Can Do About Rising Concrete

In some cases the concrete is salvageable by working around and under it, correcting the root or drainage problem that’s doing the pushing. In severe cases the slab needs to be replaced so a contractor can build a more stable, well-compacted base for the new pour. If heaving was the problem, a good installer will make certain you don’t experience it again with the new installation.

Why Concrete Sinks

Concrete sinks when voids open up beneath it. That can happen because of the natural water table in your area, flooding, poor fill, poor installation and more. Water is the usual thief: it slips under the slab, carries away supporting soil, and leaves a gap the concrete slowly settles into. Sinking concrete creates cracks and awkward walks to the car, and the void only grows if you ignore it.

What You Can Do About Sinking Concrete

Here’s the encouraging part. In most cases of cracked or sinking concrete, the slab is salvageable. Rather than busting up the concrete and replacing it, you can use mudjacking to lift the panel back into place. Mudjacking pumps a slurry into the void beneath the concrete, filling the empty space and raising the slab until the surface is level and safe again. We investigate the area first to confirm the slab is a good candidate, then walk you through the process. Only in severe cases does replacement become the better answer.

When the Movement Is Urgent

Some concrete movement can wait for a convenient season. Some can’t. Call sooner rather than later if any of these apply:

  • The lip between slabs has reached an inch or more. That’s a genuine trip hazard for kids, guests and mail carriers, and a liability question for you.
  • The slab now slopes toward your house, steering rain and snowmelt at the foundation instead of away from it.
  • A slab sounds hollow underfoot or flexes when you drive on it, which suggests a void that could give way.
  • Cracks are widening month over month instead of holding steady.

Heave tied to a growing tree also deserves prompt attention. Roots don’t shrink.

Rising and sinking concrete create real headaches for homeowners, but both have fixes. Heaved panels usually need the soil or root problem corrected, while sunken concrete can be propped back up with our help. Don’t sit back while your sidewalk or driveway turns into a liability. Call AAA Concrete Raising at (303) 526-2222 and we’ll tell you which direction your concrete is moving and what it will take to stop it.