These days the builders are more likely to build poured concrete foundations than foundations made of concrete blocks. Concrete poured has become more popular due to a variety of reasons. Wall forms that are quick to set up and taken down, concrete trucks that can travel almost everywhere, and modern pumps and admixtures which make "impossible pours" almost routine.

Despite all the advantages mentioned above, concrete block can be used as a viable foundation material. If the foundation is small -for a home addition, for instance- a builder could save money by laying a block foundation instead of outsourcing the work to foundation contractors. Likewise, crawl space foundations are able to be efficiently and quickly constructed with concrete block. And for a DIYer who has masonry expertise it gives you the opportunity to construct a foundation one block at a time.

Before getting any deeper into this "heavy" topic it's important to understand the basics of terminology. In the construction industry concrete blocks are often known as "CMUs," short for concrete masonry units. In addition to the standard 16x8x8 in. concrete block stocking most home centers, the array of CMU sizes, shapes , and the finishes on their surfaces is simply amazing. A majority retaining wall of the CMUs are specifically designed for commercial construction.

Concrete blocks are created using the same components found in concrete walls: gravel (called aggregate) and sand Portland cement and water. Lightweight blocks are sometimes called cinder blocks because they contain fly ash (cinders) which is a product of industrial combustion, is utilized as a partial substitute for heavier ingredients like sand and aggregate. The hollow cores found in many CMUs help to make the block more economical and easier to manage. Cores may be filled using concrete, foam insulation or sand to increase strength, thermal mass as well as insulation.

Contrary to what many believe, a concrete block foundation isn't necessarily superior to a poured concrete foundation, if it's constructed correctly. Both types of masonry require steel reinforcement and should be laid on a strong and stable foundation. Good drainage and damp proofing features are essential. If expansive soils or other outside forces damage the foundation of a concrete block, cracks typically appear on the mortar joints that separate individual blocks.