Page 98 - Masonry and Concrete

Understanding Masonry
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UNDERSTANDING MASONRY

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Standard concrete block measure 7- 8 in. 7- 8 in. 15- 8 in.
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actual size. The actual dimensions, plus the thickness of a 8-in. mortar
joint, equal 8 in. 8 in. 16 in. nominal dimensions. The most com-
monly used block thickness is also nominally 8 in., but nominal 4-, 6-,
10-, and 12-in. thicknesses are also available. Three modular bricks
with mortar joints are the same height as one modular 8-in. block with
one mortar joint, and two modular brick lengths with one joint equals
one modular block length (see Figure 4-3). This makes it very easy to
use brick and concrete masonry units together in the same project. It is
quite common, particularly in commercial construction, for concrete
masonry walls to serve as a structural backing for brick veneer walls or
for brick and block to be used side by side in a veneer.

4.3.2 Special-Purpose Blocks

Plain rectangular block units are called stretchers, but there are also a
number of special shapes used in CMU construction (Figure 4-10). A
few of these shapes are fairly common, including the channel or lintel
block and bond beam block, both of which can be used to build a steel-
reinforced beam to span across window and door openings. Another
special shape which can be very useful is called an open-end or “A”
block because it is shaped like the letter “A.” Masonry walls contain-
ing vertical reinforcing steel are easier to build by placing A-block
around the reinforcing bar rather than lifting and threading standard
stretcher units over the top of the bar or trying to drop the steel down
into the block core after the units are in place. The end webs of
stretcher units can also be cut away for the same ease of placement.
The newest type of concrete masonry units are interlocking retain-
ing wall blocks, which are designed to be laid without mortar. There
are several different types of systems marketed under a variety of trade
names (Figure 4-11). These new systems greatly simplify the construc-
tion of small landscape retaining walls. The cost per unit is higher
than for standard block but the savings in time and labor is substantial.

4.3.3 CMU Colors and Finishes

Ordinary concrete block are grey and have flat face shells with textures
that may range from coarse to relatively fine, depending on the aggre-
gate used and the density of the block. Architectural block come in a

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