Beyond the Block: Aesthetic Innovations in CMU Construction

Words: Peter Roberts
Photos: Spherical Block, LLC

Concrete masonry units (CMUs) have long been a mainstay of construction. They are well known as a “tried and true” material with a long history of high-strength structural performance, affordability, ease of assembly, and a long lifecycle. CMU construction features fire safety, thermal efficiency, acoustic insulation, and dimensional precision and regularity. CMUs remain a well-known staple in construction after more than 120 years in the marketplace, even within a rapidly evolving field of construction materials and methods.

Today’s CMUs include many aesthetic choices that offer exciting design possibilities and various looks for structures, limited only by the imagination of the architect and designer. The regular “gray block,” which is so familiar and common in construction, provides a starting point for aesthetic design. Long taken for granted, the regular gray block offers the distinction of providing clean walls in contrast to the horizontal striations typically found in 3D concrete-printed walls. The beauty of block begins with a known, familiar look: solid masonry walls, cleanly and regularly assembled by skilled masons.

Gray block walls serve as a clean canvas that acts to highlight other unique features of CMUs. These features include different textures, colors, shapes, sizes, and arrangements made possible by the block-making industry.

Textures
Textures can vary from the clean and dimensionally precise finish of a regular gray block to a number of different surfaces, finishes, and textures. These include smooth, polished surfaces that are ground down by the block producer. They also include the rough, textured surface of split-face block, which provides a stark and interesting contrast to the regular surface of standard CMUs or the smoother surface of ground-face block.

There can also be vertical grooves provided in the surface of split-face block, introducing an extra element of surface variation. These various textures and finishes can be arranged in geometric patterns or random arrangements for interesting variations in the textural surfaces of walls.

Colors
The colors of CMUs can be manipulated by the various types of aggregate used in block production. These can include black, gray, stark white, shades of green and amber, and numerous other colors found in various sources of aggregate. The use of colored aggregate can be further emphasized by polishing the faces of the block to highlight the different stones.

The color of CMUs can also be manipulated by including various stains and colorants as additives to the concrete mix designs. The use of stains or colorants can be complemented through the use of various colors of aggregates, creating a practically limitless number of colors available in the production of CMUs.

Additionally, the choice of sand (or smaller aggregate) can have a significant effect on the color of the resulting CMU. Sand and small aggregate may be selected to provide a brighter, whiter CMU if desired.

Finally, the type of cementitious material can affect the color of the resulting block. Different types of cement typically come in various colors and shades. A relatively new addition to cementitious materials is that of geopolymers. While this material is not yet widely available, it is increasingly of interest due to its higher temperature ratings (for fire resistance) and resistance to chemical corrosion. Geopolymers also provide the extra beneficial feature of having a substantially lower carbon footprint than traditional Portland cement.

The author has produced CMUs with his team on a small scale using novel geopolymer materials that exhibited very high strength (~4,500 psi compressive strength) and brighter, whiter colors than blocks made with regular Portland cement. When using lighter cementitious materials (such as geopolymers), the addition of stains and colorants tends to appear brighter in the resulting concrete.

Shapes
A broad array of novel shapes has been created by innovators in the realm of CMUs. These shapes can provide various types of surface relief to walls, including indentations and protrusions for interesting surface effects. These features may be randomly arranged or set in various patterns to delineate geometric features, including letters and numbers.

One particularly interesting group of block shapes is the “breeze blocks” used in CMU construction, which have been around for several decades. These breeze blocks feature through-holes within the wall, allowing the passage of air and light, which can be quite utilitarian.

These features may be desirable, especially to provide cooling or ventilation for situations and environments that need it. The lighting effects made possible by breeze blocks can create visually dramatic effects on walls, especially around entrances, foyers, and hallways.

Sizes
The sizes of CMUs vary. The standard 8-by-8-by-16-inch rectangular block is supplemented and complemented by both smaller and larger, oversized blocks. Wall thickness is typically dictated by the engineering requirements of the structure. It is worth noting that in many areas of the Caribbean, for example, wall thickness is typically only 6 inches, rather than the 8-inch wall thickness commonly found in the U.S.

All dimensions of the block can vary. All dimensions are specified to work within a modular coordination of design so that different-sized CMUs can be used alongside one another. This modular coordination allows different-sized units to be integrated into various designs to establish geometric or random patterns. Different sizes may be selected in different colors to help emphasize any given pattern or arrangement (e.g., small dark blocks with large lighter blocks). This provides yet another tool that allows for practically limitless design possibilities.

The use of oversized CMUs is a fairly recent development; these blocks are substantially larger than the traditional 8-by-8-by-16-inch units. They are usually installed with a lifting mechanism, such as the MULE (Material Unit Lift Enhancement) provided by Construction Robotics. Tools like the MULE become necessary with larger, heavier CMUs because of the increased weight. Assembly with oversized blocks can occur faster simply due to the larger unit size of the CMU.

Arrangements
CMUs can be laid in various arrangements, creating another tool for aesthetic variability and design flexibility. The obvious straight wall with square corners is complemented by patterns, including circular and curved walls; corners can be made acute or obtuse with proper detailing, which may involve having to cut block for specific features.

Novel CMUs have been developed by the author’s company, Spherical Block LLC, which are used to build roofs as vaulted arches (‘Arch’ block) and domes (‘Hex’ and ‘Pent’ blocks). The Arch block can also be used to assemble curved (cambered) archways over doors and windows, or as complete circular or round windows.

The Arch block may also be used to assemble reinforced flying buttresses, which incorporate reinforcement via curved rebar placed in receiving grooves in the block, providing a toughened arch design. These flying buttresses can help resolve thrusting or splaying forces from vertical walls that experience out-of-plane forces due to arched or domed structures sitting atop them. The use of flying buttresses made from these novel Arch blocks can create usable space on the outside wall of a structure, creating a porch or veranda area on the outside of the building and making an aesthetically dramatic visual feature.

The use of these novel CMUs to create masonry arched and domed features extends the CMU aesthetic to the top of the roof. The user finds themselves in a complete masonry building envelope, surrounded by the solid comfort and the beauty of block. Testing performed by Spherical Block LLC and Brazos Masonry near Waco, Texas, under the coordination and guidance of the MCAA in March 2026, has dramatically demonstrated the high strength of these masonry roof systems.

This dynamic testing involved dropping a 3,000-pound car from as high as 50 feet above the top of the building several times, with no apparent damage to the structure. The sense of solidity and strength that the user feels inside these buildings has been substantiated by actual testing. This sense of comfort and safety has an actual basis in empirical testing, lending credence to this aesthetic sensibility. A video recording of this dramatic testing will be revealed by the MCAA in October of this year. An observation building with a smaller, 8-foot-diameter domed roof was assembled near the test building for safe observation of this dynamic and dramatic testing.

Conclusion
The aesthetics of CMU structures include a wide range of colors, textures, arrangements, and structural features that grow from the long history of the well-known concrete block. The skilled masonry workforce provides users with the high aesthetics of craftsmanship and skilled assembly to achieve some of the highest aspirations of architecture and sophisticated aesthetics; all made possible with the beauty of block. The future holds many exciting new developments as the CMU continues to evolve into new designs, applications, and ever more elegant aesthetics.

Beyond the Block: Aesthetic Innovations in CMU Construction

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