Specify the CMU That Fits the Wall and Lift

A concrete masonry unit, or CMU, is a factory-made concrete unit laid with mortar to build walls, partitions and other masonry assemblies. “Concrete block” is the common jobsite term, but CMU is the more precise specification term.

The unit alone does not define the finished wall. Mortar, grout, reinforcing steel, joint reinforcement, ties, flashing, insulation and control joints may all affect how the assembly carries loads and manages water, heat and movement. See the parts together in this guide to a concrete blockwork wall.

Choose the wall condition and finish to identify the unit shape that belongs on the order.

CMUs Use Dry-Cast Concrete

ASTM C90-24a covers machine-made, dry-cast hollow and solid units made with hydraulic cement, water and mineral aggregates, with or without other permitted materials. It recognizes lightweight, medium-weight and normal-weight classes and permits compliant units in both loadbearing and nonloadbearing applications (ASTM International).

These units are manufactured on equipment using low- or zero-slump concrete rather than the more fluid mixtures associated with many cast-in-place applications. A unit may have hollow cells even when intended for a structural wall.

A hollow CMU is not therefore synonymous with a nonloadbearing block. Likewise, calling a product “solid” or “heavy” does not establish its strength or suitability. Use the product documentation and the standard required by the drawings.

Nominal Size Includes the Mortar Joint

The familiar 8 × 8 × 16 CMU is a nominal designation, normally read as width × height × length. Its typical specified dimensions are 7⅝ × 7⅝ × 15⅝ inches. Adding a ⅜-inch mortar joint brings the assembly back to an 8-inch module.

CMUs commonly have nominal 8-inch heights and 16-inch lengths. Common nominal widths include 4, 6, 8, 10 and 12 inches, although wider and other sizes are available. The Concrete Masonry & Hardscapes Association explains that specified dimensions are typically ⅜ inch less than nominal dimensions so the unit and mortar joint maintain the module (CMHA).

That distinction matters when laying out openings, calculating wall length or checking whether a unit fits an existing condition. Use nominal versus actual concrete masonry block dimensions before turning a nominal size into a quantity takeoff.

Each CMU Shape Has a Different Job

A takeoff that lists only “8-inch block” is usually incomplete. Common configurations include:

• Stretcher units: Used for general wall construction. A conventional hollow unit often has two cells.
• Open-end units: Fit around vertical reinforcing steel without requiring the mason to lift the unit over the top of the bar. Cell and grout layout still must match the approved details.
• Bond-beam units: Have reduced or removable webs to receive horizontal reinforcement and grout.
• Lintel units: Resemble bond-beam units but have a closed bottom to retain grout over an opening.
• Sash units: Include a molded groove for a frame or control-joint accessory.
• Half, corner and specialty units: Maintain bond, finish exposed ends or resolve specific details without excessive field cutting.
• Architectural units: Add split, ground, scored, ribbed, colored or prefaced surfaces where the masonry remains exposed.

CMHA notes that configurations and terminology vary regionally and recommends checking local manufacturer availability before specifying a particular shape. That is especially important for open-end, lintel and architectural units (CMHA).

Unit shape does not replace the wall detail. An open-end unit may simplify installation around vertical bars, but its cells, grout and reinforcement still must align with the approved design. A bond-beam or lintel unit must likewise match the required reinforcement, bearing and grout configuration.

ASTM C90 Does Not Specify the Complete Wall

ASTM C90 establishes product requirements for dry-cast loadbearing CMUs. CMHA’s summary includes dimensional tolerances, minimum face-shell and web provisions, absorption and shrinkage limits, and a minimum net-area compressive strength of 2,000 psi for compliant units (CMHA).

Compliance does not answer every project question. A usable order may also need to identify:

• Required standard and edition
• Nominal width, height and length
• Unit shape and cell configuration
• Required unit strength or masonry assembly strength
• Density class
• Color, texture and exposed faces
• Fire, thermal or acoustical requirements
• Quantities of closures, corners, bond-beam and lintel units

The standard’s edition matters because revisions can change requirements. Follow the code adopted in the project’s jurisdiction and the contract documents rather than automatically substituting the newest catalog designation.

As one code example, the 2021 IBC requires ASTM C90 units for the masonry foundation-wall provisions in Section 1807.1.6.3, alongside separate requirements for wall thickness, reinforcement, grout, mortar and bond (International Code Council). That provision is a specific foundation-wall example, not a complete specification for every CMU assembly or jurisdiction.

Pallet Weight Must Come From the Supplier

Unit weight can change with nominal width, concrete density, face-shell and web configuration, moisture condition and specialty shape. Those differences compound across a pallet. The draft source material does not provide a universal CMU or pallet weight, so one should not be assumed.

Before dispatching a forklift, telehandler, skid steer or loader, confirm with the supplier:

1. Exact CMU stock code and quantity per pallet
2. Published or scale-confirmed unit and gross pallet weight
3. Pallet dimensions and fork-entry arrangement
4. Truck type, unloading side and delivery sequence
5. Ground bearing, slope, overhead clearance and travel route
6. Machine capacity for the pallet’s actual weight, lift height and load center
7. Fork and attachment ratings, including attachment weight

Do not calculate pallet weight from a remembered “weight per block” when the shipment may contain multiple widths or specialty units. The machine also has to handle the load at the required height and load center, not merely pick it up at ground level.

Keep pallets supported and stable, protect architectural faces, and stage units close enough to the work to limit rehandling without overloading slabs or scaffolds. Separate or clearly mark specialty units so bond beams, lintels, corners and standard stretchers do not become mixed in the stack.

CMU Cutting Requires Silica Controls

Sawing concrete block can release respirable crystalline silica. OSHA’s guidance for stationary masonry saws calls for an integrated water-delivery system that continuously feeds the blade under its Table 1 control method; the saw must be operated and maintained according to its instructions. Enclosed work may also require ventilation, and water around electric equipment introduces GFCI and connector requirements (OSHA).

The better production choice is often to order the required halves, corners, bond beams and open-end units rather than create every condition with field cuts. That can reduce cutting and dust, but the approved wall details—not convenience—still control the unit schedule.

A complete CMU order identifies the standard, size, shape, properties and finish, then connects that schedule to the wall design and handling plan. “Concrete block” identifies the category; the exact unit is what must fit the detail, pallet and machine.