If you are looking to construct a building that will last for years or possibly even generations, concrete masonry unit, or CMU, walls will help it endure the test of time. CMU walls' wide range of patterns and textures make them not only attractive options for exterior and interior walls, but also reliable choices for a solid foundation. Knowing how a CMU wall operates and what materials tie the structure together will help you determine whether this bearing wall support is appropriate for your building project.

credit: Photos.com/Photos.com/Getty Images
CMU walls are laid out along a line and elevation.


Concrete masonry units act as bearing wall supports for residential homes and buildings, supporting vertical loads such as floor joists, arches, vaults and roof rafters, and horizontal loads like wind and seismic activity. The majority of present-day buildings are built using concrete blocks or bricks, which form CMU walls. Similar to stone masonry units, a CMU system stacks together concrete blocks using mortar joints. However, some CMUs are motarless systems that fit into each other through a series of interlocking tongues and grooves.


The units forming the wall can either be made from precast concrete blocks or cast-in-place concrete blocks. These blocks come in a range of shapes, including stretcher blocks, header blocks, bond beam blocks and corner blocks. Precast concrete blocks are manufactured offsite and shipped to the construction site for assembly. Cast-in-place concrete blocks are poured and cured using steam at the job site. Blocks are usually made hollow to allow for insulation. In addition to concrete, CMU walls can comprise of steel, plastic foam and other composite materials for different architectural designs. For instance, CMU blocks are often pressed into steel molds during construction.


Because concrete masonry units are larger than traditional bricks, it is cheaper to lay a CMU system. Galvanized steel reinforcements strengthen CMU walls, helping it to bear more weight without cracking. CMU walls' high tolerance for heavy loads allows it to support a stone facing, or other brick, plaster and tile building components. CMU walls are also beneficial in areas that experience severe weather such as hurricanes and tornadoes. Moreover, the durability of CMU systems extends the lifetime of buildings and minimizes the need for constant maintenance.


One of the drawbacks of CMU walls is that they absorb significant amounts of moisture. As a precaution, CMU walls are usually covered with a protective glaze or "weatherproofed" to prevent water penetration. CMU systems are heavier than wood or metal and lack flexibility for walls with different shapes and dimensions. Concrete blocks also occupy large amounts of space, since their low thermal resistance value makes them difficult to insulate. Finally, hiring contractors can be expensive depending on the geographic region.