Terminology

• CMU: concrete masonry unit
• Nominal vs. actual size: nominal includes a 3/8 in. mortar joint; an 8x8x16 unit measures 7-5/8 in. by 7-5/8 in. by 15-5/8 in.
• f'm: specified compressive strength of the masonry assembly, set by the unit strength method or prism tests
• Face shell / web: outer walls and cross walls of a hollow unit
• Partially grouted / fully grouted: grout only in reinforced cells and bond beams, or in every cell
• Bond beam: horizontal course of U-shaped or knock-out units with grout and reinforcing
• Joint reinforcement: ladder or truss wire in bed joints for crack control
• CJ (control joint): vertical joint that relieves shrinkage of the concrete units
• Lintel: reinforced CMU, precast, or steel member over an opening
• Equivalent thickness: solid thickness of a unit's concrete volume (percent solid times actual thickness); drives fire rating
• Single wythe / multi-wythe: one unit thick, or two layers tied together
• Integral water repellent: admixture in units and mortar that reduces water absorption in exposed single-wythe walls

Standards

Sizes

• Widths (nominal): 4, 6, 8, 10, 12 in.; 8 in. most common for bearing and exterior walls
• Face size: 8 in. by 16 in. nominal; half-high and other sizes for architectural units
• Coursing module: 8 in. vertical, 8 in. horizontal half-unit module; set openings and wall lengths on the module

Fire resistance

• Rating depends on aggregate type and equivalent thickness, from TMS 216 (ACI 216.1) calculation tables
• Lightweight aggregate units reach a given rating at a smaller equivalent thickness than normal-weight units
• Grouted or filled 8 in. units and many filled 6 in. units reach 4 hours per CMHA (formerly NCMA) data
• Ungrouted hollow units: confirm equivalent thickness from the manufacturer for the rating needed

Test standards

• ASTM C90: loadbearing concrete masonry units (C90-23 current); minimum net-area compressive strength has long been 1,900 psi average, with higher-strength units common
• ASTM C129: nonloadbearing units
• ASTM C270: mortar (Types M, S, N, O); Type S common for exterior and below-grade walls, Type N for above-grade nonbearing
• ASTM C476: grout
• ASTM C1314: masonry prism testing for f'm
• TMS 402 and TMS 602: design and construction specification for masonry
• TMS 216 / ACI 216.1: calculated fire resistance

Materials

• Normal-weight units: highest strength and mass for bearing, acoustic, and below-grade walls
• Lightweight units: lighter to lay and better fire rating per inch
• Architectural units: split-face, ground-face, burnished, and fluted finishes for exposed walls
• Insulated units: foam inserts or proprietary cores; still bridge through webs
• Reinforcing: ASTM A615 deformed bars in grouted cells; ladder or truss joint reinforcement in bed joints
• Grout: fine or coarse grout; self-consolidating grout for tall lifts
• Water repellents: integral in units and mortar plus post-applied sealers on exposed single-wythe walls

Detailing

• Lay out walls, openings, and heights on the 8 in. module to avoid cut units
• Control joints at changes in height or thickness, at openings, and at regular spacing set by the designer or CMHA guidance
• Bond beams at floor and roof bearing, at tops of walls, and as needed for lintels
• Reinforcing and grouted cells shown on structural drawings; keep cells aligned vertically
• Single-wythe exterior walls: integral water repellent, flashing and weeps at bases and openings, and sealed joints; consider a drained cavity or rainscreen where wetting is high
• Insulation: interior furring, exterior continuous insulation with cladding, or cavity insulation in a CMU-backup cavity wall
• Coordinate embeds, anchor bolts, and electrical boxes before grouting

Uses

Specific uses

• Load-bearing walls in schools, warehouses, retail, and low- to mid-rise housing
• Stair and elevator shafts and other fire-rated enclosures
• Backup walls for brick, stone, and metal panel cavity walls
• Gymnasiums, corridors, and back-of-house areas where abuse resistance matters
• Foundation, basement, and site walls

Pros and cons

Pros

• Fire-resistant, noncombustible, and durable under impact
• Combines structure, enclosure, and finish in one trade
• High thermal mass and good sound isolation when grouted
• Widely available units and labor

Cons

• Labor-intensive and weather-sensitive; slower than framing or tilt-up
• Shrinkage cracking without control joints and joint reinforcement
• Single-wythe walls leak without careful water management
• Low R-value through units and webs; needs added insulation
• Heavy, increasing foundation and seismic design demands

Manufacturing and cost

Construction

• Units machine-molded from zero-slump concrete and steam or moisture cured
• Laid by masons in mortar beds; face shell or full bedding per design
• Reinforcing placed in cells; grouted in lifts with consolidation
• Special inspection levels follow the structural design and risk category

Main manufacturers and suppliers

• Echelon (Oldcastle APG)
• County Materials
• Basalite Concrete Products
• Angelus Block

Trade associations: Concrete Masonry and Hardscapes Association and The Masonry Society.

Typical costs

• 8 in. hollow ungrouted wall, installed: $14 to $18 per sq ft of wall
• 8 in. partially grouted, reinforced wall, installed: $18 to $24 per sq ft of wall
• Fully grouted, architectural, or 12 in. walls: $24 to $32 per sq ft of wall
• Mason labor is 50 to 65 percent of installed cost

Sources

• CMHA: TEK 07-01D fire resistance rating of concrete masonry assemblies, https://www.cmha.org/resource/tek-07-01d/
• Masonry Advisory Council: fire resistance of masonry units, https://masonryadvisorycouncil.org/wp-content/uploads/2019/10/Fire-Resistance-of-Masonry-Units.pdf
• ASTM: C90-23 loadbearing concrete masonry units listing, ASTM C90-23 1.12.2023 | Technická norma | NORMSERVIS s.r.o.
• Concrete Products: NCMA proposal on ASTM C90 strength floor, NCMA weighs proposal for 100-psi boost in ASTM C90 – Concrete Products
• University of Houston: 04 22 13 reinforced unit masonry specification, https://www.uh.edu/facilities-services/departments/fpc/master-specs/04-22-13-struct-reinforced-concrete-unit-masonry.pdf
• Terrapin Construction Group: CMU wall construction cost per square foot, 2026, CMU Block Wall Cost (2026): $14 to $32 Per SF Installed
• Wikimedia Commons: Concrete Masonry blocks.jpg, by Salil Kumar Mukherjee (CC BY-SA 4.0), https://commons.wikimedia.org/wiki/File:Concrete_Masonry_blocks.jpg