Concrete Foundation Settling

Identification

• Cracks, bulges in the basement or crawlspace walls, or a leaning house are signs of concrete foundation settling. Settling occurs on either a vertical or horizontal axis, and the type of damage that appears tells you which way the foundation is settling. Downward settling creates large cracks in the concrete that may extend into the walls of the home. Leaning or bulging walls, especially in the basement, indicate horizontal settling.

Causes

• Frost heave is a common cause of foundation settling. When the moisture in soil freezes, it expands and exerts pressure upward on the bottom of the concrete slab. Tree roots, droughts that lower the soil moisture content, and poor soil compaction also lead to settling, according to Foundation Supportworks. Loss of moisture and large roots shift the soil and reduce support for the foundation. Concrete must be poured over properly compacted soil or the weight of the structure will cause the concrete to sink into the soft ground below.

Prevention

• Foundation-settling prevention begins before the concrete slab is poured. Aske the Builder suggests the soil at your home site be professionally tested to ensure it is compacted enough to prevent the structure from sinking. If the soil doesn't compact well, you need to have fill dirt brought in to create a stable base for the home. Avoid planting trees that mature to have large root systems right next to the foundation as well to prevent root damage.

Solution

• A settling or sinking foundation requires some form of additional support to correct the problem. Two of the most successful methods for repairing a settled concrete foundation are known as piering and slabjacking, according to the Concrete Network. Slabjacking involves pumping high-strength grout below the sunken areas of the foundation. Steel posts are driven into the soil below the foundation in piering. The posts are adjusted with hydraulic jacks to raise and support the foundation.