NCMA TEK
National Concrete Masonry Association
an information series from the national authority on concrete masonry technology
ARCHITECTURAL CONCRETE MASONRY UNITS TEK 2-3A
Unit Properties (2001)
Keywords: architectural units, burnished, fluted, ground Specification for Loadbearing Concrete Masonry Units, ASTM
face, glazed, offset face, prefaced, raked, ribbed, sandblasted, C 90 (ref. 3). In some cases, noted below where applicable,
scored, slump, split-face, split-rib, striated additional provisions govern which are more applicable to the
specific unit.
The units described herein are some of the more common
INTRODUCTION architectural concrete masonry units. However, manufacturers
may carry additional products not listed here, and conversely,
One of the most significant architectural benefits of de- not all products listed will be available in all locations. Consult
signing with concrete masonry is its versatility – the finished a local manufacturer for final unit selection.
appearance of a concrete masonry wall can be varied with the
unit size and shape, color of units and mortar, bond pattern, Architectural Unit TYPEs
and surface finish of the units. The term “architectural concrete
masonry units” typically is used to describe units displaying Split Faced Units
any one of several surface finishes that affects the texture of Split faced units have a natural stone-like texture produced
the unit, allowing the structural wall and finished surface to by molding two units face-to-face, then mechanically splitting
be installed in a single step. them apart after curing, creating a fractured surface. Because
Architectural concrete masonry units are used for inte- coarse aggregate is also fractured and exposed in this process,
rior and exterior walls, partitions, terrace walls, and other aggregate selection can alter the final appearance.
enclosures. Some units are available with the same treatment Split-faced units can also be manufactured with ribs or
or pattern on both faces, to serve as both exterior and interior scores to provide strong vertical lines in the finished wall.
finish wall material, increasing both the economic and aes- Rough textures, like those available with split face units, are
thetic advantages. Architectural units comply with the same often used in areas prone to graffiti, as the texture tends to
quality standards as conventional concrete masonry, Standard discourage graffiti vandals.
(a) Split Face and Glazed (b) Fluted Split Face (c) Split and Ground Face
Figure 1—Examples of Architectural Concrete Masonry Units
TEK 2-3A © 2001 National Concrete Masonry Association (replaces TEK 2-3)
Split face units are governed by ASTM C 90, which in- Ribbed Units
cludes an allowance to account for the rough face. ASTM C 90 Ribbed concrete masonry units (often called fluted units)
prescribes minimum faceshell thickness requirements for all typically have 4, 6, or 8 vertical ribs which align to form
loadbearing concrete masonry units, but also contains a vari- continuous vertical elements in the finished wall. The ribs
ance for split face units where up to 10% of a split faceshell are molded into the unit using a special mold. The ribs may
can be less than the minimum specified thickness, but not less have either a rectangular or circular profile, and may be either
than 3/4 in. (19 mm). This 10% limit does not apply, however, smooth or split for added texture. Figure 1b shows an example
when the units are solidly grouted. Walls utilizing a variety of a wall using ribbed (fluted) split face units.
of split face units are shown in Figure 1. The ribs can be manufactured to project beyond the overall
unit thickness (i.e., the unit thickness including ribs is thicker
Soft Split than a typical CMU), or with the rib projection included in
A soft split unit is produced using a special mold which the overall unit thickness. In the first case, the net area, and
textures the face of the unit as it is removed from the mold. corresponding section properties, will be larger than those
The appearance from a distance is very similar to that of a split published for non-ribbed units, although the effect of this
face, while a closer inspection shows a surface that is not as increase is typically neglected in structural calculations. In
well defined as that achieved with a conventional split face. In the second case, where the rib projection is included in the
addition, aggregate is not fractured in a soft split as it is in a overall unit thickness, the designer should be aware that the
conventional split face unit. As a result, the final appearance actual bearing area, section modulus, and moment of inertia
is not significantly affected by aggregate choice. are less than those published for non-ribbed units.
When building concrete masonry walls, mortar is typically
Scored Units placed to all outside edges of the masonry unit. However, with
Scored concrete masonry units are manufactured with ribbed units, it is difficult to properly tool the mortar due to
one or more vertical scores on the face to simulate additional the projections.
mortar joints in the wall. Scored units reduce the perceived
scale of the masonry while still allowing construction using Ground Face Units (Burnished, Honed)
full sized units. The scores are molded into the face of the unit Ground face concrete masonry units are polished after
during manufacture. Units with one vertical score are most manufacture to achieve a smooth finish which reveals the
common, and give the appearance of 8 in. x 8 in. (203 x 203 natural aggregate colors. The units have the appearance of
mm) units laid in stack bond. Units may also be available polished natural stone. The finished look of the ground surface
with 2, 3, 5, or 7 vertical scores. Figure 2a shows units with can be altered by changing aggregate type and proportions.
3 vertical scores in a standard sized ground face block. Often, specific aggregates will be used to enhance the appear-
It is usually desirable to lay units so that scores or ribs ance of the polished surface (Figure 1c and 2a), while coatings
align vertically when the units are placed. This may require are sometimes used to deepen the color. Ground face units are
different bond patterns, depending on the configuration of the often scored to achieve a scale other than the conventional 8
scores or ribs. For example, units with two and five scores x 16 in. (203 x 406 mm), as shown in Figure 2a.
can be placed in either stack bond or in a one-third running
bond to align scores in adjacent courses. Other appropriate Sandblasted Units
bond patterns are included in Table 1. Note that varying bond Sand (or abrasive) blasting is used to expose the aggregate in
patterns can impact how the wall responds to structural loads a concrete masonry unit and results in a "weathered" look.
(see ref. 1).
(a) Scored and Ground Face (b) Glazed (c) Slump Block
Figure 2—Additional Examples of Architectural Concrete Masonry Units
Striated (Raked) Units pigment used, cement color, aggregate color, and the amount
Striated units achieve an overall texture by means of small of water used in the mix (a wetter mix will generally produce
vertical grooves molded into the unit face. The striations are lighter and brighter colors). Both white and gray cements are
most often random, to achieve a naturally rough look, but are available. The use of white cement results in more vibrant
sometimes available in uniform striation patterns. Striation can colors, but also increases cost. The aggregates used in the
be applied to scored and ribbed units as well (see Figure 3c). concrete mix also impact the final appearance. Because of these
varying factors, there are typically some subtle variations in
Glazed (Prefaced) Units color among units. When units must be exactly the same color
Glazed concrete masonry units are manufactured by to achieve a particular architectural effect, uncolored units
bonding a permanent colored facing (typically compsed of should be used, then painted or stained the desired color.
polyester resins, silica sand and various other chemicals) Variegated units provide color variations within each unit,
to a concrete masonry unit, providing a smooth impervious producing a marbled effect. These units are manufactured by
surface. The glazed facings must comply with ASTM C 744 mixing two different concrete colors into the same unit mold.
(ref. 4), Standard Specification for Prefaced Concrete and
Calcium Silicate Masonry Units, which contains minimum Standard Unit Nomenclature
requirements for facing quality and dimensional tolerances. In
addition, the unit to which the facing is applied must comply As with many construction products and systems, there
with ASTM C 90 when used in loadbearing applications. The are often regional differences in terminology for the same type
glazed surface is waterproof, resistant to staining and graffiti, of architectural concrete masonry units: ribbed and fluted,
highly impact resistant, as well as being resistant to many ground and burnished, etc. The National Concrete Masonry
chemicals and bacteria. Special admixtures and mortars are Association has developed a standardized nomenclature (see
available for use with glazed units that provide better stain, Table 1) which can be used to avoid confusion when specifying
bacteria, and water penetration resistance. and supplying masonry units. (See Figure 3 for examples).
Glazed units are available in a variety of vibrant colors,
pastels, earth tones, and even faux granite and marble patterns. Table 1 – Standard Unit Nomenclature (ref. 2)
They are often used for brightly-colored accent bands, and in
gymnasiums, rest rooms, and indoor swimming pools where Each unit is described using a three-part code in the following format:
the stain and moisture resistant finish reduces maintenance. XX YYY WWHHLL, where “XX” describes the number of scores
Kitchens and laboratories also benefit from the chemical and or ribs, “YYY” describes the architectural finish, and WWHHLL
bacteria-resistant surface. describes the overall nominal unit dimensions for width, height,
and length. The various codes are described below.
Offset Face Units Scores or Ribs:
Units with an offset face produce a very highly textured 00 no scores or ribs, applicable for any running bond
wall, with strong patterns of light and shadow. The offsets 01 one score, applicable for one-half running bond (units overlap
make it appear as if adjacent units are staggered. This effect is the unit above and below by one-half the unit length)
accomplished by using a unit mold with the desired offsets. 02 2 scores, applicable for one-third running bond
03 3 scores, applicable for one-half or one-quarter running
Slump Block Units bond
Slump block concrete masonry units have a rounded face 04 4 ribs, applicable for one-half or one-quarter running bond
05 5 scores, applicable for one-half running bond
that resembles handmade adobe. They are more commonly
06 6 ribs, applicable for one-half running bond
available in the Southwest United States where adobe is part 07 7 scores, applicable for one-half or one-quarter running
of the architectural heritage. Conventional concrete masonry bond
units are manufactured using a “no-slump” concrete mix, 08 8 ribs, applicable for one-half or one-quarter running bond
which holds its shape when removed from the manufactur-
ing mold. Slump units, on the other hand, are manufactured Architectural Finish:
using a concrete mix that slumps within desired limits when BN1 bullnose unit with 1 in. (25 mm) radius bullnose
removed from its mold (see Figure 2c). BN2 bullnose unit with 2 in. (51 mm) radius bullnose
Slump unit widths may vary as much as 1 in. (25 mm). For SCV vertically scored unit
GRF ground face unit
this reason, the structural design should assume the actual width of
MDC circular ribs, rib projects beyond the overall unit thickness
slump units is 1 in. (25 mm) less than the nominal dimension. MNC circular ribs, rib projection included in overall unit thickness
MDR rectangular ribs, rib projects beyond the overall unit thickness
COLOR MNR rectangular ribs, rib projection included in unit thickness
STR striated unit
Architectural concrete masonry units are often integrally STS striated unit, 1 in. (25 mm) uniform striation pattern
colored to enhance the appearance or achieve a particular effect. STT striated unit, 1/16 in. (1.6 mm) uniform striation pattern
Concrete masonry units are colored by adding mineral oxide SPF split face unit
pigments to the concrete mix. Mortars can also be integrally NPF split face ribbed unit, rib projections included in unit thickness
colored to blend or contrast with the masonry units. SLP slump block
The final unit color varies with the amount and type of **Q locally provided product
08 MNR 080816 06 MNC 080816
8 x 8 x 16 Rectangular ribbed unit 8 x 8 x 16 rounded ribbed unit
(rib projection included in (rib projection included in
overall unit thickness), overall unit thickness),
with 8 ribs with 6 ribs
Figure 3a—Rectangular Ribbed Unit Figure 3b—Rounded Rib Unit
01 STR 080816 00 BN1 120816
8 x 8 x 16 striated corner unit 12 x 8 x 16 Bullnose Unit with
striated patterns are often 1 in. (25 mm) radius bullnose.
applied to scored or ribbed
units
Figure 3c—Striated Scored Unit Figure 3d—Bullnose Unit
Figure 3—Examples of Standard Unit Nomenclature
References
1. Concrete Masonry Bond Patterns, TEK 14-6. National Concrete Masonry Association, 1996.
2. Concrete Masonry Shapes & Sizes Manual, CM 260A. National Concrete Masonry Association, 1997.
3. Standard Specification for Loadbearing Concrete Masonry Units, ASTM C 90-00. American Society for Testing and Ma-
terials, 2000.
4. Standard Specification for Prefaced Concrete and Calcium Silicate Masonry Units, ASTM C 744-99. American Society for
Testing and Materials, 1999.
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accuracy and the application of the information contained in this publication.
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