Sunken Sidewalk or Patio in Thornton? Mudjacking vs. Foam Leveling vs. Replacement

A sidewalk panel that dropped an inch, a patio tilting toward the house, a gap opening up where the driveway meets the garage. Sunken concrete is one of the most common problems around Thornton homes, and it's more than an eyesore. Uneven slabs are trip hazards, and a slab that tilts toward your foundation sends water right where you don't want it. The good news is that sunken concrete doesn't always need to be torn out. Here's how slab leveling works, how mudjacking and foam leveling compare, and when replacement is the better call.

Why concrete sinks in the north metro

Concrete slabs are only as stable as the ground underneath them. When the soil under a slab settles, washes out, or shifts, the slab follows it down. Around Thornton, a few things usually cause it:

Poorly compacted fill. Soil around a newer house's foundation is backfill, and if it wasn't compacted well, it keeps settling for years. That's why patios, stoops, and walkways right next to the house so often sink.
Water washing out the base. Downspouts that dump onto or next to a slab, broken sprinkler lines, and low spots where water pools can erode the soil underneath.
Expansive clay. Much of the area has clay soils that swell when wet and shrink when dry. That movement can lift slabs in one season and drop them in another, as the Colorado Geological Survey explains.
Freeze-thaw. Water that gets under a slab and freezes can heave it, and then it settles unevenly when it thaws. Our guide to why Thornton driveways crack every winter covers that in more detail.

Option 1: Mudjacking (slabjacking)

Mudjacking is the traditional way to lift a sunken slab. The crew drills holes through the concrete and pumps a cement-based slurry underneath. As the slurry fills the void, it pushes the slab back up. Then the holes get patched.

Pros: It's a proven method that has been around for decades, and the material is basically soil and cement.
Cons: The holes are larger, so the patches are more noticeable. The slurry is heavy, which can add weight to soft soil, and it takes a while to cure before the slab can carry full loads.

Option 2: Polyurethane foam leveling (polyjacking)

Foam leveling works the same basic way, but instead of slurry the crew injects an expanding polyurethane foam through smaller holes. The foam expands, fills the voids, and lifts the slab.

Pros: Smaller holes and patches, a much lighter material, and it cures quickly, so you can usually use the area soon after. The foam doesn't wash out the way loose soil does.
Cons: It usually costs more per job than mudjacking, and results depend a lot on the installer's experience. Lifting too fast or too much can crack a slab.

When replacement is the better choice

Leveling only works if the slab itself is still in decent shape. It's usually time to replace the concrete instead when:

The slab is broken into many pieces or has wide, crumbling cracks.
The surface is badly scaled, pitted, or flaking.
Tree roots are pushing the slab up (lifting won't fix heaving from roots).
The slab is very old and you'd be lifting something that's near the end of its life anyway.

Leveling a badly damaged slab just gives you a level, badly damaged slab. A good contractor will tell you honestly which side of that line your concrete is on.

Fix the water, or it'll sink again

Whatever method you choose, ask what caused the settling in the first place. If a downspout is dumping onto the slab, a sprinkler line is leaking, or the slab slopes toward the house, fixing that is what keeps the repair from failing. After leveling, the joints and cracks should be sealed so water doesn't keep getting underneath. If your slab tilts toward the foundation, getting it sloped back away from the house is a big deal for keeping your basement dry.

Questions to ask a concrete leveling contractor

Do you recommend mudjacking, foam, or replacement for my slabs, and why?
What do you think caused the settling, and what should I do about it?
How noticeable will the drill holes and patches be?
Will you seal the joints and cracks afterward?
Is there a warranty if the slab settles again?

What does leveling cost?

It depends on the size and number of slabs, how far they've dropped, and the method. For a rough starting point, our concrete cost calculator uses published Denver-area ranges from RemodelerIQ and Colorado Concrete Repair. It's a general estimate, not a quote.

Get your slabs back to level

Whether it's a sunken sidewalk or front step, a tilting patio, or a driveway that's dropping at the garage, concrete repair and leveling can often fix it without starting over. We connect homeowners in Thornton, Northglenn, Westminster, and the north metro with local concrete contractors for free estimates, in English or Spanish. Fill out the form or call (720) 984-1238.

Concrete Driveways & Patios, Thornton: Get a Free Estimate Call Now: (720) 984-1238