Concrete curb ramp work in progress during an accessibility upgrade

HOMEOWNER FIELD NOTES

Is my slab sinking?

A new trip edge. A puddle that never used to be there. A gap opening at the step. Here’s what those signs mean and what to do before you call.

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Photo: Oregon DOT / Wikimedia Commons · License

WHY SLABS SINK

It’s the dirt, not the concrete.

01Poured on loose fill
Fill dirt near new houses often isn’t compacted well. The slab sits level at first.
02Water moves the soil
Downspouts, broken sprinkler lines, and freeze-thaw wash soil out or let it settle. A gap opens under the slab.
03The slab drops
With nothing under one end, it tips into the hole. Now water runs toward the house and pools on the low side.

Fix the water source too, or the new fill can wash out the same way.

BEFORE / AFTER

What the crew is actually fixing.

Sidewalk panels that dropped below the curb and the next slab, leaving a raised edge — **Trip edge, water pooling.** One end sank into a washed-out pocket. Panels no longer line up and rain runs the wrong way.

Technician injecting polyurethane foam through a slab while a dial gauge on the next panel tracks the lift — **Lift while watching a gauge.** The tech injects through the slab while a dial indicator on the next panel shows exactly when it’s level.

After

Flush joints, drainage restored. The void is filled, the slab sits back at grade, and the holes are patched. Same concrete, no tear-out.

Photos: credits & licenses. Diagrams are illustrations, not to scale.

THE 60-SECOND CHECK

Concrete doesn’t sink.
The dirt under it does.

Water washes out or softens the soil, a void opens, and the slab drops into it. Catch it early and a lift fixes it. Wait, and the slab cracks into pieces that have to be replaced. This is a homeowner checklist. It doesn’t replace a site visit.

Signs worth documenting

A slab edge sits noticeably lower than an adjacent panel.
Water consistently collects in the same area after rain or washing.
A step, stoop, walkway, or driveway panel has shifted relative to its neighbor.
A gap has opened between concrete and a fixed feature such as a wall or step.
Cracks or unevenness appear to be changing over time.

Before you call

Take a photo from the same spot each month and lay a level or straightedge across the joint. Hose the area down and watch where the water goes. Bring those photos to the estimate. A crew can quote faster when it can see the drop getting worse.

Questions to ask

Can the slab be lifted safely, or does it need another repair?
What observations support the recommended method?
Are drainage, soil, broken concrete, or structural issues outside the scope?
What does the written quote include, and how will the final elevation be checked?