Page 85 - Masonry and Concrete

Understanding Masonry
84 CHAPTER FOUR

be “dry-stacked” without mortar if the units have an interlocking
shape or if a special surface-bonding mortar is applied to hold the
units together. Natural stone is also usually set in mortar, but can be
dry-stacked for walls of modest height used in landscaping applica-
tions. In addition to units and mortar, most masonry projects will
include accessory items such as anchors, ties, flashing, or joint rein-
forcement. These accessories are as important to successful structural
and functional performance as the units, mortar, and workmanship.
Masonry that is used as a facing material over a nonmasonry backing
wall is called veneer (Figure 4-1). Veneers are typically only one unit in
thickness. Freestanding masonry walls may be one unit or more in
thickness depending on the type of masonry and the wall design. Walls
that are only one unit in thickness and are not anchored to a backing
wall are called single-wythe walls. Double-wythe walls are two units in
thickness. If the space between the wythes is less than one inch, it is
called a collar joint and is filled solidly with mortar or cement grout. A
space wider than one inch between wythes is called a cavity, and may
be either open or filled with grout or grout and steel reinforcing bars.
Double-wythe walls with an ungrouted cavity are called cavity walls.
Both cavity walls and veneer walls are designed to drain water through
the open space between wythes or the space between the veneer and its
backing wall. Insulation can also be installed in this space to increase
the thermal resistance or R-value of the wall.
In most residential construction in the United States, masonry is
used as a veneer over wood stud or metal stud framing. Veneers are
nonstructural and support only their own weight while transferring
wind loads to the backing wall. Masonry is strong enough to serve as a
loadbearing structural wall which supports the floors and roof of a
structure. Loadbearing masonry was once very common in both resi-
dential and commercial construction but was gradually surpassed in
popularity by concrete, steel, and wood framing after the turn of the
century. Contemporary loadbearing masonry is stronger and more eco-
nomical than historic loadbearing masonry, and new structural
masonry systems are gaining popularity again among home builders.
Like concrete, masonry is strong in compression but requires the
incorporation of reinforcing steel to increase resistance to tension
(pulling) and flexural (bending) stresses (Figure 4-2). Masonry will not
burn, so it can be used to construct fire walls between units or areas of

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.