CMU Shape Guide: Block Types, Dimensions, and Specification for Contractors
Choosing the wrong CMU shape can mean costly field modifications or failed inspections. This guide covers the standard and specialty concrete masonry unit shapes manufactured by Ernest Maier and Parker Block, how they are dimensioned, and what contractors and specifiers need to know when calling out block on drawings or in the field.
What Is a CMU Shape?
A CMU shape refers to the cross-sectional profile and face configuration of a concrete masonry unit. Beyond the basic hollow rectangular block most people picture, there is a wide range of shapes designed for corners, bond beams, control joints, lintels, and architectural finishes. Selecting the right shape at the specification stage saves labor and reduces waste during installation.
Standard CMU Shapes
Stretcher Block
The stretcher is the most common CMU shape. It is the standard hollow unit used in the field of a wall. Nominal dimensions are typically 8x8x16 inches (actual: 7-5/8 x 7-5/8 x 15-5/8 inches), though 4-inch, 6-inch, 10-inch, 12-inch, 14-inch, and 16-inch widths are available. Two hollow cores run through the unit to reduce weight and allow vertical reinforcing and grout placement.
Corner Block
Corner blocks have one flat end and one recessed end, allowing the exposed face at a 90-degree corner to look clean and consistent. They are used at building corners and wall ends where the stretcher web would otherwise be visible. Specify corner blocks for any exterior corner on an architectural masonry wall. Bullnoses can also be incorporated into corner blocks to yield rounded corners.
Bond Beam Block
Bond beam units have a depressed or open-bottom core, creating a horizontal channel across the course. Horizontal rebar and grout are placed in this channel to tie the wall together laterally. Bond beams are typically required at floor lines, roof connections, and specific intervals per structural drawings.
Lintel Block
Lintel blocks are U-shaped units used above door and window openings. They form a continuous channel that is reinforced and grouted to act as a structural beam spanning the opening. Lintel block is the masonry-integrated alternative to precast concrete lintels for standard CMU wall construction.
Header blocks are designed in an L-shape to accommodate a lintel that will span several block and carry load over an opening. Header blocks can be solid or hollow. The notch is at the midpoint of the block’s depth and width.
Control Joint Block
Control joint blocks are modified units designed to create a vertical plane of weakness in the wall. They allow the masonry to crack predictably at the control joint rather than randomly across the wall face. Common types include open-end and scored units that align vertically to create a continuous joint.
Specialty and Architectural CMU Shapes
Split-Face Block
Split-face CMU has a fractured, textured face created during manufacturing. The rough surface gives an architectural stone appearance without the cost of natural stone. Split-face block is widely used for commercial facades, interior feature walls, and retaining walls where visual texture is part of the design.
Slump Block
Slump block is a low-slump unit that settles slightly during curing, producing an irregular, rounded surface profile. It gives a rustic or adobe-style appearance. Slump block is common in the Southwest and in residential applications where a non-industrial finish is preferred.
Pier Block
Pier blocks (aka column blocks or plain end block) are designed to stack and form pier or column shapes, typically square or rectangular in plan. They are used for fence columns, entry pillars, chimneys, and structural column forms that will be filled with rebar and grout.
Fluted, Embossed, Ribbed Block
Fluted and ribbed CMU units have grooves or projections on the face, creating an architectural surface pattern. They are used on commercial building facades and in interior applications where a more refined finish is desired. Brick-embossed block carries the look of brick on a full-size CMU, combining masonry appearance with block-scale installation.
How CMU Dimensions Work
CMU dimensions are listed as width x height x length in nominal inches. Actual dimensions are 3/8 inch smaller in each direction to account for the standard mortar joint. A nominal 8x8x16 block has actual dimensions of 7-5/8 x 7-5/8 x 15-5/8 inches.
This matters on drawings: always confirm whether a dimension is nominal or actual. Nominal is used for coursing and quantity calculations and pairs well with our masonry wall calculator. Actual is used for field layout and opening dimensions.
Ernest Maier CMU Manufacturing
Ernest Maier and Parker Block operate regional manufacturing plants in the mid-Atlantic. In-house production allows quality control over mix design, unit weight, and dimensional tolerances. Standard and specialty shapes are manufactured on site, which supports consistent availability for production builders and commercial projects.
For load-bearing assemblies, pair the right shape with our CMU fire rating chart and concrete lintels load tables when confirming code compliance. For large or specialty shape orders, contact Ernest Maier early in the project planning phase. Some specialty shapes require lead time.
We manufactures a complete line of normal weight and lightweight concrete masonry units and “Underwriters Laboratories fire-rated” units. In addition, we can manufacture units to metric dimensions.
In attachments, asterisk ( * ) indicates Special Order Items.
Contact Ernest Maier to discuss your project block specification and confirm availability.
FAQ
Q: What is the most common CMU shape?
A: The stretcher block is the most common shape. It is the standard hollow unit used in the field of a CMU wall, available in widths from 4 to 16 inches nominal.
Q: What is a bond beam block used for?
A: Bond beam blocks have an open or depressed core that creates a horizontal channel in the wall for placing horizontal reinforcing steel and grout. They are used to tie masonry walls together laterally at floor lines, roof connections, and intervals specified by the structural engineer.
Q: How are CMU dimensions listed?
A: CMU dimensions are listed as width x height x length in nominal inches. Actual dimensions are 3/8 inch smaller in each direction to account for the standard mortar joint. A nominal 8x8x16 block has actual dimensions of 7-5/8 x 7-5/8 x 15-5/8 inches.
Q: Does Ernest Maier manufacture CMU in-house?
A: Yes. Ernest Maier and Parker Block operate regional manufacturing plants in the mid-Atlantic. In-house production allows quality control over mix design, unit weight, and dimensional tolerances.
Q: Can I get specialty or custom CMU shapes from Ernest Maier?
A: Ernest Maier stocks a range of specialty shapes including split-face, slump, column, control joint, and lintel blocks. Custom shapes for large or unique projects can be discussed with the masonry team.
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