Today the builders are more likely to build foundations made of concrete poured than those constructed using concrete blocks. Poured concrete has become more popular for a number of reasons, including wall forms that can be easily set up and taken down, concrete trucks that can travel almost everywhere as well as modern admixtures and pumping equipment that create "impossible pours' almost common.
In spite of the benefits mentioned above, concrete block still can be used as an acceptable foundation material. When the foundation is small -for a home addition, for instance, a builder can save money by laying the foundation using block instead of subcontracting the work out to a foundation contractor. In the same way, crawl space foundations are able to be efficiently and quickly constructed using blocks of concrete. For those who are DIYers who has masonry expertise the block material offers the chance to build the foundation block by block one time.
Before getting any deeper in this "heavy" topic it's helpful to know the basics of terminology. In the construction industry, concrete blocks are called "CMUs," short for concrete masonry units. Beyond the standard 16 x 8 x 8 in. concrete block stocking most home centers, the variety of CMU sizes, shapes Phoenix , and the finishes on their surfaces is simply amazing. The majority of the selection is specifically designed for commercial construction.
Concrete blocks are created from the same ingredients found in concrete walls -gravel (called aggregate) and sand Portland cement and water. Blocks that are light weight can be referred to as"cinder blocks" because fly ash (cinders) which is a product of industrial combustion, is used as a partial substitute for more heavy ingredients such as sand and aggregate. The hollow cores of most CMUs help to make the block cheaper and easier to manage. The cores can be filled with concrete, sand or foam insulation to increase strength, thermal mass as well as insulation.
Contrary to popular opinion it is true that a block foundation made of concrete isn't necessarily inferior to a concrete foundation, providing that it's been properly built. Both types of masonry need steel reinforcement, and they must be laid on a solid and stable foundation. Proper drainage and damp proofing details are crucial. If expansive soils or other external forces harm the foundation of a concrete block cracks are typically seen on the mortar joints that divide the blocks.