The reasons why concrete becomes uneven are many, but broadly speaking they can be boiled down to four primary causes, water issues, dry soil conditions, poor compaction, and animal and pest influences. Read below to get more information on each cause of concrete settling.

Water Issues

The number one reason concrete settles is water. Heavy rain or flooding can cause soil to soften, which can cause concrete to sink. Water that freezes and thaws in winter months can also break down soil beneath a slab weakening its ability to support the concrete. Finally, water that continually flows over, and under, concrete can wash out the subsurface, leaving voids that cause the concrete to sink. This can often be a result of downspouts running directly on the ground beside concrete sidewalks or driveways, or poor grading around your concrete slabs.

Dry Soil Conditions

Long periods of dry conditions, like during a drought, can cause soils, mainly clay, to shrink. This can result in unstable sub-surfaces, and voids which often lead to sinking concrete. Also, dried out soil that is then soaked with heavy rain can also lead to sinkage due to voids being filled with now moistened soil.

Poor Compaction

During construction, sometimes contractors don’t compact the soil well enough before pouring footers or concrete slabs. This can often happen around foundations where backfill can be poorly compacted, or even worse, debris such as old tree stumps and building material can be shoved in holes before filling. When this debris rots or shifts it can result in sinking soil, leading to uneven concrete or sunken foundations.

Animal/Pest Influences

Animals such as chipmunks, groundhogs and more can burrow under concrete, creating voids. These voids can also be widened by running water causing even more issues. Even pests like ants can cause quite a bit of perforation of the soil beneath concrete causing the slabs to sink.