Sizes
| CMU Size | Nominal Dimensions (D x H x L) | Actual Dimensions (D x H x L) |
|---|---|---|
| 4" CMU (Full Block) | 4" x 8" x 16" | 3 ⅝" x 7 ⅝" x 15 ⅝" |
| 4" CMU (Half Block) | 4" x 8" x 8" | 3 ⅝" x 7 ⅝" x 7 ⅝" |
| 6" CMU (Full Block) | 6" x 8" x 16" | 5 ⅝" x 7 ⅝" x 15 ⅝" |
| 6" CMU (Half Block) | 6" x 8" x 8" | 5 ⅝" x 7 ⅝" x 7 ⅝" |
| 8" CMU (Full Block) | 8" x 8" x 16" | 7 ⅝" x 7 ⅝" x 15 ⅝" |
| 8" CMU (Half Block) | 8" x 8" x 8" | 7 ⅝" x 7 ⅝" x 7 ⅝" |
| 10" CMU (Full Block) | 10" x 8" x 16" | 9 ⅝" x 7 ⅝" x 15 ⅝" |
| 10" CMU (Half Block) | 10" x 8" x 8" | 9 ⅝" x 7 ⅝" x 7 ⅝" |
| 12" CMU (Full Block) | 12" x 8" x 16" | 11 ⅝" x 7 ⅝" x 15 ⅝" |
| 12" CMU (Half Block) | 12" x 8" x 8" | 11 ⅝" x 7 ⅝" x 7 ⅝" |
Concrete Masonry Units (CMUs) are manufactured in a variety of sizes. They are identified by their depth – i.e. the thickness of the wall they create. For instance, a 6" CMU is nominally 6" deep while a 10" CMU is nominally 10" deep.
Concrete blocks also come in half-sizes, which are helpful in reducing the need to cut blocks in the field at corners or the end of walls. The architect should always attempt to design buildings using the nominal dimensions to the nearest half-block size to reduce waste and labor due to cut blocks.
The following table provides concrete block sizes in both nominal and actual dimensions. While 4", 6", 8", 10", and 12" are the standard sizes, some manufacturers offer other sizes not listed below.
Specifications
| ASTM Designation | CMU Type |
|---|---|
| ASTM C55 | Concrete Brick |
| ASTM C73 | Calcium Silicate Face Brick |
| ASTM C90 | Load Bearing Concrete Masonry Units |
| ASTM C139 | CMUs for construction of Catch Basins and Manholes |
| ASTM C744 | Prefaced Concrete and Calcium Silicate Masonry Units |
| ASTM C936 | Solid Interlocking Concrete Paving Units |
| ASTM C1372 | Segmental Retaining Wall Units |
CMU manufacturers must conform to ASTM standards when fabricating concrete blocks.
The following table provides the ASTM standards that apply to concrete masonry units. ASTM C90 covers most conventional CMU construction and is the standard referenced by the ICC codes.
Surface Finishes
Burnished/Polished CMU
Also referred to as Ground Face CMU, concrete blocks can be burnished or polished to expose the natural aggregates in the concrete mix. It is important to work with the manufacturer to select appealing aggregate and to test the polishing process to ensure you get the aesthetic you are looking for.
Colored CMU
There are two ways a concrete masonry unit can have color. The first is by adding color pigments can be to either the concrete block or the mortar, or both. This method will have some slight variations in the color you choose due to the nature of concrete mixture. The second way to add color is by painting the block and/or the mortar.
Glazed CMU
Glazed concrete masonry units have a tile-like glazed finish made from a resin-based coating. This type of coating offers a wide variety of color as well as some faux material patterns. These surfaces may offer improved resistance to graffiti and chemicals. Glazed CMU is covered via ASTM C744, but the blocks still need to adhere to the ASTM C90 standard for load bearing CMU.
Raked CMU
Raked (also called Striated) units have vertical rake marks introduced during the molding process. The rake marks are not as deep as the scored or ribbed blocks. You can also apply rake marks to scored or ribbed blocks.
Sandblasted CMU
Sandblasting concrete masonry units also exposes the aggregate, but also blasts away some of the sand and cement to create a rougher appearance. Some people believe this creates a natural weathered look instead of the smoother look of burnished or polished CMU.
Soft-Split CMU
Soft-Split CMU is made with special molds that create a split-faced appearance instead of mechanically splitting the blocks. The effect is a bit less rough than split faced. In addition, the mold means that aggregates are not exposed.
Split Faced CMU
Split faced CMU is manufactured by molding two units side-by-side and then mechanically splitting them apart after firing. This creates a very rough texture that some people think looks like stone, especially since the aggregates in the block are also split or exposed.
