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Acronymsaka: concrete blockaka: cinder blockaka: concrete masonry unit

CMU (Concrete Masonry Unit)

In Plain English

A standard concrete block used to build walls in commercial and industrial construction.

Definition

A Concrete Masonry Unit is a standardized rectangular block manufactured from portland cement, aggregate, and water that is used in the construction of walls, partitions, and structural elements. CMUs are available in various strengths, densities, and face textures, and are specified by compressive strength per ASTM C90. They are a common and economical structural wall material for commercial, industrial, and institutional construction.

Why It Matters in Bidding

CMU is one of the most quantity-driven items on a masonry takeoff, where block counts, mortar, grout, reinforcing, and lift heights all roll into labor and material pricing. Specifying the correct ASTM C90 strength, density, and face finish affects both cost and which sub can self-perform, so estimators must read the spec closely. Misreading lightweight versus normal-weight units or special shapes can swing a masonry bid materially.

Example

Taking off a warehouse wall, the estimator counts standard 8x8x16 units by the square foot, then adds bond beam, lintel, and corner block plus grout and rebar for the reinforced cells.

Related Terms

ACI (American Concrete Institute)ASTMIBC (International Building Code)

Frequently Asked Questions

Estimators typically take off CMU walls by net square footage of wall area, then convert to block count using the unit's nominal face dimensions, commonly about 1.125 blocks per square foot for standard 8x16 units. Openings are deducted, and special shapes like bond beam, lintel, and corner block are counted separately along with mortar and grout.
ASTM C90 is the standard covering loadbearing concrete masonry units, setting minimum compressive strength, dimensional tolerances, and allowable absorption and density classifications. Specs reference it to define the structural block required. Estimators check the called-out strength and weight class because they affect unit cost, availability, and whether grouting and reinforcing assumptions are correct.
Beyond the block itself, price mortar, grout for reinforced cells, vertical and horizontal reinforcing steel, joint reinforcement, control-joint materials, flashing and weeps, anchors and ties, and any special shapes. Labor for laying, grouting lifts, and bracing tall walls is significant. Scaffolding and cleaning are often overlooked line items on larger masonry packages.

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