Concrete Masonry Units

Pre-cast concrete blocks have been around since ancient Rome and survive today as perhaps the only remaining structural use of masonry in the globalized economies of the world. Concrete masonry units (CMUs) are the modern manifestation of earlier forms of precast concrete blocks and have been in use since the 1890s. Hollow centers allow for adequate structural performance with minimal amount of material while allowing for the the incorporation of rebar for additional structural performance and stability. Engineered for economic efficiency, CMU wall construction is one of the cheapest structural systems available in building today. In addition to being relatively inexpensive, certain types of CMUs are sometimes touted as moderately sustainable in their use of fly ash or slag cement—byproducts of coal burning power plants and steel production respectively—to both reduce the amount of portland cement and aggregate as well as to capture carbon emissions from industrial production.

Although CMUs are typically chosen for economic reasons, a number of architects have taken on the CMU as an expressive or even phenomenological material. Frank Lloyd Wright famously took advantage of the formal malleability of the concrete casting process by designing ornamental molds for his “textile block system” used in a number of houses in California in the 1920s. Inspired by the ornamentation of ancient Mesoamerican architecture, Wright’s custom CMUs express both their unitized nature while accumulating into to a larger textural whole.

More recently the Minneapolis based studio LOOM developed twelve new CMU block designs that address issues of not only surface pattern but also structural strength, durability, environmental sustainability, and formal functionality. One design, for example, incorporates niches for nesting birds while another includes channels for collecting rain water.

Unlike the previous two approaches which relied on customized molds to achieve architectural expression, Silent House by Japanese architect Takao Shiotsuka accepts the standard CMU for its inherent material, spatial and tectonic qualities. The building structure and surfaces are one and the same. Exterior window and door openings are nothing more than voids within the solid CMU walls, lacking any additional framing or detailing apart from block and mortar. The interior volumes and exterior massing is determined entirely by the CMU module; never breaking the sacred rules of masonry construction which forbids the cutting of bricks.


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