The Problem – Sinking
Why Does Concrete Settle?
Poor Soil Conditions
As soils become saturated with water, the soil expands and loses strength. This condition allows slabs to sink – just like standing in wet mud. This can occur from heavy rains, melting snow or plumbing leaks.
Many homes are built on backfilled soils. If the soil is not compacted correctly before construction, backfill may gradually compact unevenly, sometimes settling significantly as quick as a year. The now sunken soils create a cavity under the concrete. The concrete then sinks to the supporting soil levels.
Trees and large shrubs can consume up to 30 gallons of water a day. If located near concrete, the loss of water in the soil will make the soil contract and may cause the slabs to settle. Decaying tree roots can create voids under concrete.
Improper drainage can cause soil instability by creating saturated soils, which allows the slabs to settle. Poor drainage can be typical of an area, or as minor as a misplaced down spout. Also, improper drainage can remove soil and create voids by the process of erosion.
What Signs to Look For
Cracks and Crumbling
Since concrete is one of the strongest building materials in the world, any significant wear and tear is cause for concern. Cracks and crumbling could be superficial and simply the sign of weathering, but it also could indicate a more serious underlying problem: the lack of foundational stability. If the soil is eroding beneath the slab, cracks and crumbling could only be the beginning of the issue. Sinking and shifting could be next, so make sure you get a full assessment of the slab
Pooling water on the concrete isn’t good news. It means there is likely sinking or shifting beneath that is causing the concrete to hold precipitation and impede drainage. Since concrete is a porous material, it’s best to not have standing water on it for long periods, so raising the slab surface to facilitate drainage might help.
Porches or Patios Pull Away from Foundation
When you see your front stairs or your back patio begin to pull away from the foundation, it’s probably not the foundation that’s moving — it’s the concrete base of your steps or patio. This signifies a lack of support beneath and the soil has shifted or eroded, so it’s imperative to lift and stabilize the structure before it causes further damage.