Concrete Masonry Units are one of the most versatile products in the construction industry. They can provide the structural frame of a building and they can also serve as a strong backup system for many types of veneer systems. Concrete Masonry Walls can even be the veneer system itself with options such as smooth face, split-face, ground face, polished face & glazed face units. Concrete Masonry Walls used in a single wythe application can serve in both a structural capacity and also be the finished face of the wall. They can provide the thermal mass necessary to help reduce heating and cooling costs. Concrete Masonry Walls can provide redundancy for increased fire-safety in the event sprinkler systems malfunction during a fire. They also provide an inordinate amount of sound control wherever used. So you see, concrete masonry units can do many jobs.
Concrete Masonry Units (CMU) can be used as a veneer cladding system. Veneer units are typically 4” wide x 8” high x 16” long (nominal dimensions). They are available in a multitude of colors and textures including split-face, ground face, polished face and glazed face. Using a properly built CMU veneer with an air space, appropriate flashings, rigid continuous insulation and a CMU backup provides a high degree of water penetration resistance, energy efficiency, and a reduction in unwanted exterior sound.
Using Reinforced Concrete Masonry Units along with hollow core concrete plank as the structural frame provides an economical solution for many types of buildings particularly those with repetitive floor plans such as dormitories, apartments, condos, hotels and motels. Not only is a CMU/hollow core plank system a quick, coordinated building system but the finished product can provide a high degree of sound control and fire safe walls between units.
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Concrete Masonry Walls do not burn. Depending on the thickness of the wall, the density of the units and the amount of grout used, concrete masonry walls can provide up to a four hour fire rating. Additionally, concrete masonry walls pass the hose stream test unlike other fire rated wall systems.
Concrete Masonry Walls provide a high level of sound control. This can be advantageous if used in either interior walls between units such as apartments or dormitories or even on exterior walls as the backup to control unwanted outside noise. CMU walls can provide Sound Transmission Class (STC) ratings up to 63 depending on the wall thickness, density of the units and whether they are fully grouted or not.
Concrete Masonry Units are governed by ASTM c90 – Standard Specification for Loadbearing Concrete Masonry Units. This specification covers both hollow and solid units suitable for both loadbearing and non-loadbearing applications. There are 3 density classifications for CMU; Lightweight (less than 105 lbs./cf.), Medium Weight (105 to less than 125 lbs./cf.) and Normal Weight (125 lbs./cf. or more). The minimum net area compressive strength of all 3 densities is the same at 2000 lbs./in2 according to ASTM c90. However, higher compressive strengths can be specified but suppliers should be consulted to determine their availability. Please consult ASTM c90 for a more comprehensive review of the specifications governing concrete masonry units
The International Masonry Institute (IMI) is a strategic alliance between the International Union of Bricklayers and Allied Craftworkers and the contractors who employ those members. Through education, technical support, research and training the IMI works to provide a more efficient construction delivery system.