Figure 8-14.-Installing a closure block.
important. First, tip it slightly toward you so that you
can see the edge of the course below. Then place the
lower edge of the new block directly on the edges of
the block below (figure 8-13). Make all position
adjustments while the mortar is soft and plastic. Any
adjustments you make after the mortar stiffens will
break the mortar bond and allow water to penetrate.
Level each block and align it to the masons line by
tapping it lightly with a trowel handle.
Fifth and last, before installing the closure block,
butter both edges of the opening and all four vertical
edges of the closure block with mortar. Then, lower
the closure block carefully into place (figure 8-14). If
Figure 8-15.-Cutting off excess mortar from the joints.
any mortar falls out, leaving an open joint, remove the
block and repeat the procedure.
To assure a good bond, do not spread mortar too
far ahead when actually laying blocks. If you do, the
mortar will stiffen and lose its plasticity. The
recommended width of mortar joints for concrete
masonry units is 3/8 inch. When properly made, these
joints produce a weathertight, neat, and durable
concrete masonry wall. As you lay each block, cut off
excess mortar from the joints using a trowel
(figure 8-15) and throw it back on the mortar board to
rework into the fresh mortar. Do not, however,
rework any mortar dropped on the scaffold or floor.
Weathertight joints and the neat appearance of
concrete masonry walls depend on proper striking
(tooling). After laying a section of the wall, tool the
mortar joint when the mortar becomes thumb print
hard. Tooling compacts the mortar and forces it
tightly against the masonry on each side of the joint.
Use either concave or V-shaped tooling on all joints
(figure 8-16). Tool horizontal joints (figure 8-17,
view 1) with a long jointer first, followed by tooling
the vertical joints (view 2). Trim off mortar burrs
from the tooling flush with the wall face using a
trowel, soft bristle brush, or by rubbing with a burlap
Figure 8-16.-Tooled mortar joints for weathertight exterior