A spread footing is a type of the shallow foundation, which is defined as the structural members used to support a column and walls. The spread footing is used in foundation repair as it also transmits and distributes the load coming on the structure to the soil beneath it.
To create a spread footing, a three-foot by three-foot square haunch is dug out below the existing structure that is filled with concrete, and reinforced with rebar. It is ideal for retaining walls, wing walls, areas with shallow rock, enclosed patios, or anything lacking a grade beam.
When it comes to foundation repair, the foundation systems that are used for low-rise residential buildings are suitable for their light loads, and nearly all are supported on spread footings. Spread footings come in two types, continuous footings that support walls and isolated pad footings that support concentrated loads. The footings themselves are made from concrete poured directly on undisturbed soil to a minimum depth of about 30 centimetres. Typical continuous concrete footings usually support a foundation wall that acts as a retaining wall to form a basement, or it could act as a frost wall that has earth on both sides. Foundation walls can be built from reinforced concrete or masonry, particularly concrete blocks.
Concrete blocks are a standard size larger than bricks, and are they are hollow and able to form a grid of vertical planes. They are the least expensive form of masonry—using cheap but strong material—and their large size economizes on the labour required to lay them. Their appearance and weathering properties are inferior to those of fired masonry, but they are satisfactory for foundation walls. Sometime in foundation repair, timber foundation walls and spread footings are used. Excavation for foundations is the most highly mechanized operation in this building type; it is done almost entirely with bulldozers and backhoes.
The spread footing may be circular, square, and rectangular, and it transmits and distributes the load from the structure over the larger area of soil beneath it for providing greater stability. Spread footing has very little risk of failure as compared to other types of footing, and it increases the life of the buildings by controlling the damage in the structures. Spread footing has several points of contact with the structure, and it will be able to provide support to the structure continuously. The spread footing is easy to provide in the building structures.
The cons to this system are that it requires five to seven days of cure time, and has limited uses in foundation repair. Long term stability can be affected if there is negative drainage, or the bottom of the footing is still in the active clay.