Concrete Masonry Block
in Scotts Valley, CA

A concrete masonry unit, or CMU, is a building unit made from Portland cement, aggregates, and water, cured under controlled conditions and quality-tested for compliance with ASTM standards. Modern units can be produced with up to 30% recycled content. The terms concrete block, cinder block, and CMU all get used for the same product, though cinder block properly refers to the older type.

Age, mostly. Cinder blocks were popular in the early 20th century and used coal-combustion byproducts — cinders — as lightweight aggregates to reduce the weight of the unit. Modern CMUs are made from Portland cement and aggregates instead. Lightweight units today can run up to 46% lighter than traditional concrete blocks without giving up compliance.

Most concrete blocks in the US are 16 inches long and 8 inches high nominal, with width setting the wall thickness. Four-inch, six-inch, eight-inch, and twelve-inch widths cover the range, and blocks can be solid or hollow with two or more cores. Nominal dimensions include the mortar joint, so the unit in your hand measures smaller than the number on the spec.

Yes, and load-bearing walls are one of the most common CMU applications in residential and commercial buildings. Load-bearing units must meet ASTM C90, and compressive strength across the category runs from roughly 3.4 to 34.5 MPa depending on the unit. Solid CMUs are denser and the ideal choice where load is concentrated. Hollow units carry structural capacity once grouted and reinforced.

Yes. Concrete blocks work for foundations and basement walls because of their strength, and they are also used in retaining walls for landscaping and civil engineering. Careful drainage design matters more here than anywhere else on a block job — CMU walls need proper detailing for moisture control, or infiltration becomes a permanent problem behind a finished wall.

Properly reinforced with steel rebar and grout, CMU walls withstand seismic activity well. Fully grouted walls are required in high-seismic zones, and California building codes are specific about it. Reinforcing goes in as the wall goes up, since grout follows the steel rather than the other way around. Bring the engineer's specification, and we will match the units and the grout to it.

Usually. Standard concrete blocks have low R-values and often need additional insulation to meet energy codes, even though CMUs offer excellent thermal retention that flattens daily temperature swings. Hollow units can be filled with insulation to improve thermal properties, which is one of the reasons hollow blocks dominate on exterior walls.

Concrete masonry units made to be seen. Architectural blocks come in numerous colors and textures — split face for a fractured stone look, ground face for a smooth finish, polished face resembling marble or granite, and antique finishes with a shot-blast texture. Split face blocks still meet ASTM C90 for load-bearing use, so visual appeal does not cost structural strength.

Fire-rated partition walls, sound separations between units, and non-load-bearing walls where mass matters more than structure. CMUs are noncombustible, which makes them useful in fire-rated construction, and dense blocks reduce sound transmission between rooms. Four-inch and six-inch widths handle most interior partition work.

On lifecycle cost, usually. Blocks are widely available and cost-effective as material, though they are labor-intensive to install and need skilled masons to lay properly. Block often costs more to put up than framing and less to own over the life of a building, which is what decides most commercial and municipal work.

Both. Contractors buy by the cube with delivery scheduled to a build calendar. Homeowners buy by the piece and get the same material advice at the counter. Tell us the application and the wall height, and we will point you at the right unit.