What Is A CMU Wall?
CMU Wall stands for Concrete Masonry Units Wall are environmentally friendly and versatile building products that can be used for a wide variety of applications. These blocks are available in a variety of shapes and sizes available, they can be used as part of attractive exterior design, as well as to add interest to interior walls. CMU blocks used in the project can even contribute to it being designated as a “green” building.
CMU Wall Details (Concrete Masonry Units)
CMU blocks are made from Portland cement, aggregates, and water. As a building material, CMU blocks offer several attractive characteristics to designers and builders, including the following:
- Easy to install
- Low maintenance
- Decorative finishes available
- Ornamented after installation
CMU Block Size
CMU blocks are manufactured in a variety of sizes. They are distinguished by their depth – i.e. the thickness of the wall they create. For Example, a 6″ CMU is nominally 6″ deep while a 10″ CMU is nominally 10″ deep.
These blocks also come in half-sizes, which are helpful in reducing the need to cut blocks in the field at corners or the end of walls. The architect always tries to design buildings using the nominal dimensions to the nearest half-block size to reduce waste and labor due to cut blocks.
The nominal and actual sizes of CMU blocks are given in the below table. In which a CMU blocks having size 4″, 6″, 8″, 10″, and 12″ are the standard sizes, some manufacturers offer other sizes not listed below
|CMU CCMU Blocks Size||NOMINAL DIMENSION D x H x L|
|4” Full Blocks||4″ x 8″ x 16″|
|4” Half Blocks||4″ x 8″ x 8″|
|6” Full Blocks||6″ x 8″ x 16″|
|6” Half Blocks||6″ x 8″ x 8″|
|8” Full Blocks||8″ x 8″ x 16″|
|8” Half Blocks||8″ x 8″ x 8″|
|10” Full Blocks||10″ x 8″ x 16″|
|10” Half Blocks||10″ x 8″ x 8″|
|12” Full Blocks||12″ x 8″ x 16″|
|12” Half Blocks||12″ x 8″ x 8″|
Read More: 10 Types Of Retaining Wall With Full Details
Standard CMU Block Wall Detail
CMU manufacturers must conform to ASTM standards when fabricating concrete blocks. The standards identify appropriate materials, compressive strength, dimensional tolerance, moisture absorption, and other performance characteristics.
Concrete brick is made from concrete similar to concrete block, but concrete bricks are fabricated in sizes that match traditional clay bricks (i.e. 2 2/3″ tall).
The following table provides the ASTM standards that apply to concrete masonry units. ASTM C90 covers most conventional CMU construction and is the standard referenced by the ICC codes.
|ASTM DESIGNATION||TYPE OF CMU|
|ATSM C55||Concrete Brick|
|ASTM C73||Calcium Silicate Face Brick|
|ASTM C90||Load Bearing Concrete Masonry Units|
|ASTM C139||CMUs for construction of Catch Basins and Manholes|
|ASTM C744||Calcium Silicate Masonry Units and Prefaced Concrete|
|ASTM C936||Solid Interlocking Concrete Paving Units|
|ASTM C1372||Segmental Retaining Wall Units|
CMU Block Shapes
CMU blocks are available in infinite varieties of shapes in the market. The following image shows the popular types of CMU blocks shapes.
CMU Block Weight
The weight of CMU blocks varies depending on the density of the concrete mix used.
There are three classifications of CMU:
1) Lightweight CMU Blocks = Weight less than 105 lb/ft3,
2) Medium weight CMU Blocks = Weight between 105 lb/ft3 and 125 lb/ft, and
3) Normal weight CMU Blocks = Weight more than 125 lb/ft3.
Lighter CMUs are less expensive, require less labor to install, and tend to have better fire resistance properties. Heavier units tend to reduce sound transmission, have much higher compressive strengths, and have greater thermal storage capacity; however, they are more expensive and cost more to install. Architects must specify the CMU weight if a particular weight is required.
CMU Blocks Compressive Strength
The CMU blocks and masonry walls Compressive strength varies from approximately 1,000 psi (7 MPa) to 5,000 psi (34 MPa) based on the type of concrete used to manufacture the unit, quality of mortar used.
CMU Wall Construction
Generally, all walls constructed with CMUs follow the same elements, although the application of those elements can vary considerably depending on the size, shape, and use of the wall.
Foundation. All CMU walls must rest on a firm and hard foundation of poured concrete. The foundation depth and size will vary depending on the size of the concrete block wall and the weight it must support. But, generally, the depth of foundation must be at least twice as wide as the wall itself and which extends about 1 foot down below the frost line.
CMU block. The selection of shape and size of blocks generally taken to match the function of the wall and the configuration of the wall. Most CMU walls will use several different types of blocks, especially stretchers and corner units.
Mortar joints. Each layer of the joint is connected to adjoining blocks with either type N (above grade) or type S (below grade) mortar. For higher-strength of walls, they are constructed such as so the vertical joints are offset (staggered) from one course to the next.
Reinforcement. The freestanding wall is not strong enough to resist the stresses that can crack joints and destroy walls, so both vertical and horizontal reinforcement is common. Vertical reinforcement in the form of straight length steel bar is embedded in wet concrete that is poured into block cavities at prescribed intervals. Horizontal reinforcement is provided with strips of metal laid into the wet mortar after every third or fourth course of block.
Most cmu house construction are single-wythe walls, which means they are constructed from single-wide rows of block stacked one over the other. In case, there is a need for higher structural strength you can construct double-wythe walls, in which two courses of blocks are laid together.
CMU Block Cost
CMU block cost is $3 per square foot for split-face concrete or cinder units and add $9 to $12 per square foot for installation labor, supplies, and equipment. A completed, 100-square-foot project will cost between $1,200 and $1,500, depending on the difficulty of the installation. An average 100-square-foot wall will run about $1,350.
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