Page 148 - Masonry and Concrete

Masonry Construction Techniques
147
MASONRY CONSTRUCTION TECHNIQUES

QUICK>>>TIP
Bricks are cut with a wide mason’s chisel called a
brickset. Soft brick can usually be cut with one sharp blow. Harder brick
must be scored on all sides, then severed with a final sharp blow. Con-
crete block and stone are cut with a power saw equipped with a masonry
blade. For making only a few cuts, a circular saw may be adequate, but
for larger projects, a table-mounted masonry saw can be rented or pur-
chased. Stone is often wetted while sawing to cool the blade and con-
trol dust, but concrete masonry units should never be wetted because
this will increase the moisture content and the possibility of shrinkage
cracking in the wall.

in. plywood or the tip of a finger can be used to evenly space between
units. If necessary, the size of the head joints between units can be
adjusted to take up slight variations in brick size, footing length, or
brick ledge dimensions. Each concrete block and head joint should
measure 16 in., each modular brick and head joint should measure 8
in., and every three bricks with head joints should be 24 in. The size of
“antiqued” Type FBA brick will vary more than those of smoother FBS
brick, so the head joint width will also have to vary more to maintain
the modular dimensions of a wall. The wall length should lay out
using only whole and half-length units. Half-size brick units should be
cut where needed for openings, wall ends, and corners. After the head
joints are adjusted for even coursing, a few joint locations or opening
locations or other critical dimensions can be marked along the chalk
line on a footing or on the face of a brick ledge so that they can be used
to check the spacing of the first course when the units are later laid in
mortar.

5.2.4 Masonry Units
When brick is manufactured, it is fired in a high-temperature kiln
which drives virtually all of the moisture out of the wet clay. Fired
bricks are extremely dry until they absorb enough moisture from the
air to achieve a state of moisture equilibrium with their surroundings.
Brick that is very dry when it is laid causes rapid and excessive loss of
mixing water from the mortar, which results in poor adhesion, incom-
plete bond, and water-permeable joints of low strength. Brick that is
very dry and absorptive is said to have a high initial rate of absorption

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.