Nowadays, builders are more likely to use concrete foundations that are poured rather than foundations constructed using concrete blocks. Poured concrete has become more popular because of a variety of reasons, including wall forms that can be quickly built and then removed and concrete trucks that can be used almost anywhere and the latest admixtures and pumping equipment that allow "impossible' pours almost routine.

Despite the many advantages discussed above, concrete block still is an appropriate foundation material. If the foundation isn't too big -for a home addition, for instance- a builder could save money by laying a block foundation instead of outsourcing the work to foundation contractors. In the same way, crawl space foundations can be easily and cost-effectively constructed with blocks of concrete. 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 in this "heavy" topic it's important to understand some terms. In the world of construction concrete blocks are often known as "CMUs," short for concrete masonry units. Beyond the standard 16x8x8 in. concrete block stocked by most home centers, the vast universe of CMU sizes, shapes and surface finishes is truly amazing. Most of this selection is intended for commercial construction.

Concrete blocks are made from the same ingredients used in poured concrete concrete block wall walls, which are gravel (called aggregate) as well as sand, Portland cement, and water. Blocks that are light weight can be referred to as"cinder blocks" because fly ash (cinders), a waste product from industrial combustion, can be used to substitute more heavy ingredients such as sand and aggregate. The hollow cores in most CMUs allow the block to be much more affordable and easy to work with. The cores can be filled with concrete foam insulation, or sand to improve their strength, thermal mass, and insulation.

Contrary to popular opinion it is true that a block foundation made of concrete isn't necessarily inferior to a concrete foundation, provided that it's been properly built. Both types of masonry need steel reinforcement and must be laid on a solid and stable foundation. Proper drainage and damp proofing features are vital. If expansive soils or other external forces harm the foundation of a concrete block cracks usually appear on the mortar joints that create the separation between individual blocks.