Sunken flag / sunken slab A sunken flag or sunken slab is a section of concrete that has settled below the surrounding pavement. The lowered surface often creates uneven walking conditions and drainage problems.
Sunken slabs usually develop because of soil settlement, erosion, poor compaction, or underground utility activity. Besides creating trip hazards, they can allow water to collect on the pavement, accelerating deterioration. Lasting repairs typically address both the slab and the supporting foundation beneath it.
Frequently Asked Questions About Sunken flag / sunken slab
What is a sunken sidewalk flag?
A slab that has settled below the surrounding pavement, creating an uneven surface and often a low spot that holds water.
What causes a flag to sink?
Soil settlement, erosion beneath the slab, poor compaction during original construction, or disturbance from underground utility work.
Why is ponding water a problem?
Standing water accelerates concrete deterioration, freezes into an ice hazard in winter, and can itself be cited as a drainage defect.
Can a sunken flag just be lifted?
Lifting methods exist, but a lasting repair addresses the failed support beneath the slab, not just its elevation.