Concrete Masonry Unit (CMU) is a composite construction blocks that consists of aggregates (gravel and sand), a cementitious material (Portland cement, slag cement, or blended cement), and water. Concrete can be cast in almost any shape desired of the CMU block either hollow or solid. Concrete Masonry Units (CMUs) is usually gray concrete block but it does have a variety of surface textures and colors for aesthetic looks of the wall.
The most common finish on concrete masonry units is a smooth or rough texture, which is achieved by applying different types of aggregates to the surface of the blocks. Other finishes include color, which is achieved by adding pigments to the mix during production, and patterned textures that are created with a trowel after the block has been poured.
All the details of surface finishes of concrete masonry units are given in details;
1. Colored – Concrete Masonry Unit (CMU)
A variety of coloring pigments can be added to the concrete masonry units during the casting or one can add the coloring pigments to the mortar for attaining the colorized surface finishing of the concrete masonry units.
1.1 Coloring Varieties for CMU
Coloring pigments are available in variety of colors and combination of several colors can also be used to blend them together to get new color variations. Following are most common colors that are used in CMUs.
- Blacks
- Browns
- Greens
- Reds
- Whites, etc.
How to achieve consistent Surface Coloring of CMU?
The consistent surface coloring of the concrete masonry units can be attained by following the two methods:
Mixing Coloring Pigments during Casting
Even if the material engineer orders the colored concrete masonry blocks from the same manufacturing plant, there will be seen a variation in coloring. Even during blending and casting, there can be few areas in which coloring pigments are much getter in quantity then elsewhere. Thus, consistency in coloring is questionable sometimes.
- The material engineer or the architect must get at least 3 samples of colorized concrete blocks to verify the consistency in coloring from a given manufacturer.
- Randomly selected concrete blocks should be checked in each batch of transport.
1.2 Painting the CMU Wall Surface
Second option for getting consistent coloring is to paint the CMU surface or plaster the CMU blocks with a colored mortar. By this way one can certify the uniform coloring on the CMU walls. Make sure the architect is taking the coloring manufacturer into confidence about the selection or output of the desired color for CMU.
2. Glazed – Concrete Masonry Unit (CMU)
Glazed concrete masonry units are prepared as conventional concrete blocks but the surface is covered with resin-based coating that provides a tile like ceramic glaze finishing. Numerous glazing options based on coloring and faux patterns are available in the market.
2.1 Use of Glazed Concrete Masonry Units
Glazed CMU offer better
- Resistance to against corrosive chemicals,
- Durable against extreme weathers and
- Provide protection against graffiti.
2.2 ASTM Code for Glazed Concrete Masonry Units (CMU)
All Glazed Concrete Masonry Units must adhere to the standards set forth by the ASTM codes that are given below for reference;
| S.NO. | ASTM Code | ASTM Code Title |
|---|---|---|
| 1. | ASTM-C90 | Standard Specification for Loadbearing Concrete Masonry Units |
| 2. | ASTM-C744 | Standard Specification for Prefaced Concrete and Calcium Silicate Masonry Units |
| 3. | ASTM-C1405 | Standard Specification for Loadbearing Concrete Masonry Units |
3. Split Faced – Concrete Masonry Unit (CMU)
Two concrete blocks are manufactured together and mechanically split into two halves after the block has been put on firing operation. Thus named as Split Face Concrete Masonry Unit (CMU).
3.1 Surface Finishing of Split Faced CMUs
Split faced CMU gives a natural touch similar to rocks as after splitting the aggregates specially the coarse aggregates are visible thus giving a soothing appearance rather then artificial beauty.
3.2 Suitability of Split Faced CMUs
Split Faced CMUs have rough appearance thus suitable for external walls. Scored Units and Ribbed Units of CMUs can also have Split Faces.
4. Soft Split – Concrete Masonry Unit (CMU)
Soft Split Concrete Masonry Units are manufactured in a shaped formwork or molds that are already having a split. Hence when concrete is casted into such mold, the fresh concrete attains the shape of Split Concrete Masonry Unit. No need of mechanical splitting is involved.
4.1 Surface Finishing of Soft-Split CMUs
Soft-Split CMUs give smooth surface as compared to the Split Faced CMUs that are having rough surface.
4.2 Strength of Soft-Split CMUs vs Split CMUs
Strength of Soft-Split CMUs is higher then Split Faced CMUs as mechanical splitting creates weakness and cracks in the concrete masonry unit.
5. Polished – Concrete Masonry Unit (CMU)
Polished CMUs are also known are Burnished Concrete Masonry Units. In this type of surface finishing of CMUs, concrete masonry blocks are polished with the help of grinding machine to get a smooth surface and to expose the inner section.
It is important that the coarse aggregates are of good quality and appeasing color, as upon exposure due to polishing operation that will give a pleasent appearance. Polishing operation needs a control too and must be discussed with the manufacturer before hand.
6. Sandblasted – Concrete Masonry Unit (CMU)
Sandblasting is carried out on concrete masonry units in order to expose the inner surface to give the appearance of a truly weathered concrete block. Sandblasting may score the sand and coarse aggregates.
6.1 Sandblasted CMUs vs Polished CMUs
Some people consider Sandblasted CMUs better then Polished CMUs are sandblasting gives rough texture as compared to smooth surface of Polished CMUs, thus giving natural weathering touch.
7. Raked – Concrete Masonry Unit (CMU)
Vertical rake markings are introduced during the molding process in raked or striated concrete masonry units. The rake markings aren’t too deep but are on the surface of CMUs and give a nice texture to the block.
7.1 Combination of Ribbed and Raking CMU
In addition to that one can optionally request that scored or ribbed blocks be textured with an extra raking pattern. Many other such combinations can be obtained too.
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