A normal block or concrete masonry unit (CMU) is made from Portland cement and sand or fine gravel. Lightweight blocks are produced by using aerated concrete or lighter weight aggregates. The very firm concrete is pressed into moulds under intense pressure and then the formed block is cured in an autoclave or humidity controlled environment.

Blocks are usually produced with hollow centres to reduce weight and improve insulation. These voids also allow rebar and concrete to run vertically through the block to create stronger, load-bearing walls (reinforced concrete).

Block is available in many sizes but the standard size is 20cm x 20cm x 40cm (8in. x 8in. x 16in.); the actual size is usually about 1cm smaller to allow for mortar joints.

Architectural block (courtesy Shouldice Designer Stone)

The surface which forms the outside of a wall can be formed using numerous profiles in smooth face or split face and in many colours from pure white through a range of blended colours to almost black.

While traditionally used as a structural material, block can be used as a versatile cladding material as well.  Architectural block has gained popularity for its variety of finishes, achieved through scoring, splitting, grinding, and/or polishing for a unique look with high structural integrity.

Modern styles of architecture across the world have even embraced the utilitarian appeal of the concrete block by incorporating it into their overall design.  Projects such as Frank Lloyd Wright’s Ennis Houseeven featured block walls inside and out.

Frank Lloyd Wright, Ennis House, Los Angeles (stylized block)