You’ve probably seen sunken concrete slabs on sidewalks or pavements around your neighboorhood. There are a variety of reasons why concrete slabs sink and settle, but the primary cause for sunken concrete are changes in the soil beneath the cement. Whether the soil foundation is compacted, undergoes drying and shrinking, or becomes washed out by the elements, concrete slabs begin to settle in a sunken fashion because of the void that is left below the slab. If the concrete is not strong enough to withstand the void, the cement slabs will eventually crack, break, and settle into a new formation, becoming uneven with all of the other slabs in the surrounding area.
What is Concrete Settlement and Why is It an Issue?
Cement that settles along the sidewalk or on a driveway may not pose a structural threat to the buildings and homes around it. It can present a physical danger of tripping, falling, and injuring people and vehicles. Concrete settlement can cause serious damage when it occurs in places that are directly related to the foundation and structure of a building. Noticing uneven cement, cracking or shifting in the pavement of your porch, basement, or concrete around the exterior of your home could be an indication of shifting soils. Soil erosion, washout, and drying can be a major problem for the stability of any home or structure.
What is Concrete Drying and Shrinking?
When soils beneath a concrete floor slab become dry and shrink, the foundation takes on a new shape and form. Moisture in the soil causes it to expand and become fuller than when it is dry. Dry soil will shrink and create unwanted space below the concrete slabs, causing them to settle on the newly formed foundation. If the partition walls and structural foundation of your home begin to settle with the sinking concrete slabs, cracking in the drywall will occur.
What is Concrete Washout?
It is a common practice to install plumbing lines underneath concrete slabs. If those plumb lines start to leak, it can cause the soil foundation to wash away, leading to settlement and cracking. Washout is not always preventable, and it often goes without detection until the concrete slabs above the plumb lines become cracked.
Concrete settlement is fairly common in homes and buildings across the United States. Understanding what causes concrete slabs to settle is important for knowing how to repair and fix concrete that becomes broken and cracked.
Concrete Settlement FAQs
The primary cause of sunken concrete is changes in the soil beneath the slab, including compaction, drying and shrinking, or washout from the elements. These shifts create voids under the concrete, causing slabs to settle unevenly and eventually crack or break.
Settled concrete presents real physical dangers including tripping, falling, and vehicle damage -- and when it occurs near a home's foundation, porch, or basement, it can signal serious structural instability. Uneven or cracked concrete in those areas should be inspected promptly.
As soil loses moisture, it shrinks and creates unwanted gaps beneath the concrete slab, causing it to settle into the newly formed void. If the surrounding walls and foundation shift along with it, cracking in the drywall and structural elements of your home can follow.
Plumbing lines installed beneath concrete slabs can leak over time, gradually washing away the surrounding soil and creating voids that lead to settlement and cracking. Washout often goes undetected until the concrete above the affected area visibly shifts or breaks.
Concrete settlement is extremely common in homes and buildings throughout the United States due to the natural behavior of soil over time. Understanding its root causes -- erosion, drying, and washout -- is the first step toward knowing when and how to repair it.