A slab can sink because the material supporting it changes—not because the concrete itself suddenly became shorter. In Florida, common possibilities include washed-out fill, poor original compaction, buried organic material, drainage failures, soil-volume changes and, in some regions, true subsidence. The repair should follow the cause rather than the advertisement.
Common Support-Loss Paths
| Possible contributor | What happens below the slab | Clues to investigate |
|---|---|---|
| Water erosion / washout | Moving water carries fines away and leaves voids. | Downspouts, irrigation, failed joints, pool-shell edge, drainage outlets, storm damage. |
| Poorly compacted fill | Placed soil consolidates after construction. | Settlement near excavated areas, utilities, additions, pool backfill or driveway edges. |
| Organic or buried debris | Material decomposes or compresses and loses volume. | Localized sinking with no obvious surface washout. |
| Broken drainage/plumbing component | Leakage can remove or soften supporting material. | Persistent wet area, unusual water use, soil movement near buried piping. |
| Broader subsidence | Ground elevation changes below more than one surface. | Multiple structures affected, depressions, widening cracks, doors/floors/walls changing. |
Not Every Florida Depression Is a Sinkhole
The Florida Geological Survey explicitly warns that several subsurface events can mimic sinkhole activity, including compressed organic layers, broken sewer or drain pipes, broken septic tanks, improperly compacted soil and buried debris. Until a qualified investigation identifies the mechanism, “subsidence incident” is often a more accurate description than declaring a sinkhole.
Pool Decks Have a Special Backfill History
An in-ground pool requires excavation, followed by backfill around the shell and deck-support area. That makes compaction, drainage and water movement around the pool relevant when a deck settles. Published Florida stabilization projects also document voids and support loss near pool decks after washout and changing moisture conditions.
Fix the Water Path Before Paying for the Finish
If runoff, leaking irrigation, an open joint or another water source is washing support away, simply lifting the slab can restore elevation without removing the mechanism that caused the void. The proposed repair should explain both the support correction and the recurrence-control plan.