Concrete that sounds wrong before it looks wrong
There's a stage before a slab sinks, and most Centennial homeowners walk over it every day without knowing. The soil underneath has washed out or shrunk away, the slab is bridging an empty pocket, and everything up top still looks perfect. The giveaway is sound, not sight. Knock on the slab with a steel rod or a screwdriver handle: bedded concrete answers with a dull thud, bridged concrete rings hollow. That hollow spot is a void, and packing it solid now costs a fraction of lifting the slab after it drops.
Two creeks, one direction: down
Centennial's clay soils feed the Cherry Creek and Piney Creek systems, which means nearly every lot in the city has water crossing it on the way to somewhere lower. Lots along the drainage sides see it constantly. That steady movement is what undermines slabs here: each storm and each spring melt carries a few grains of base soil off toward the creek, and after enough seasons a garage apron or a porch footing is resting on less ground than it was built over.
The east side gets an accelerant. Hail exposure means storm cells that dump water hard and fast, and clay that baked tight between storms sheds that water sideways instead of drinking it. Sideways is where your slab edges are.
Three more void-makers we trace on Centennial estimates:
- Plumbing leaks under or beside slabs in these 30-to-50-year-old homes. The leak gets repaired; the soil it flushed away stays gone.
- Dry-year shrink. Expansive clay pulls down and away from the slab bottom during drought stretches, and the gap doesn't close when moisture returns. The soil squeezes around the slab instead of back under it.
- Old trench lines. Utility and sprinkler trenches backfilled in the 80s keep consolidating under load, and any slab crossing one ends up bridging it.
Fill it standing, or lift it fallen. One is cheaper.
Void fill and slab leveling use the same truck, the same 1.5" holes, and the same Portland cement, sand, and topsoil slurry. The difference is timing and pressure. A fill happens while the slab still sits at grade: we pump at low pressure until the pocket packs solid, and the slab never moves. A lift happens after the drop, takes more material and more pressure, and costs accordingly. Most Centennial void fill jobs land between $400 and $1,500. Catch the same problem after the slab falls and you're pricing a full lift, or worse, a crack that turns one slab into five pieces nobody can lift.
Sometimes a slab has dropped a little and voided underneath besides. We handle both in one visit, pumping until the slab returns to grade with a solid bed under it. Howard sorts out which situation you have during the estimate, and he's talked plenty of homeowners out of the big repair because a small fill solved it. That honesty is why plumbers and inspectors around the metro keep handing out our number.
Half a day, back in service by dinner
A fill visit moves quickly. We confirm the void with the rod, drill, pump until the hollow tone goes solid, patch flush, and sweep up. Half a day on site covers most jobs, and the area is back in service the same day. Cold weather doesn't postpone the work; the slurry cures fine in winter, and only ground frozen too hard for clean drilling costs us a day or two of waiting. We also run larger fills for HOAs and property managers around Centennial: under footings, behind retaining walls, beneath common-area slabs, with a 10-yard truck that doesn't pause the pour for refills.
Worth a call if any of this sounds familiar
A hollow knock near the garage door. A soft, sunken feel at a slab edge after spring melt. An inspection report from a home sale flagging voids under the porch. A plumbing leak that was just fixed anywhere near concrete. Each one is the cheap version of a problem that gets expensive on its own schedule. The estimate is free, and it's the fastest one we do: Trevor brings the steel rod, taps the slab with you standing there, and you hear the answer for yourself before anyone talks price. Call (303) 526-2222 or book the tap test. For the background, read how voids form under concrete.