180 Section 4 Reading Prints
drying shrinkage. If the slab cracks, the reinforce-
ment will keep the crack tight. Reinforcement is
also used when the concrete slab is expected to be
subjected to tension due to the settling of a dirt fi ll
or heavy load. A typical note specifying welded
wire fabric or reinforcing steel in a concrete fl oor
would read as follows:
5″ THK SLAB w/6×6–W10×W10 WWF (for mesh)
or
#4 @ 18″ O.C. EW OVER ABC GRAVEL SUBBASE
(for reinforcing steel rods)
Expansion Joints
Expansion joints are placed between a
slab and a wall, and also around columns,
Figure 10-14. These joints prevent the slab from
cracking due to expansion and contraction. They
are used with slabs-on-grade that do not settle
evenly with the footings and foundation walls.
Other expansion joints may be used in long slabs.
These usually call for premolded joints and have
metal coverings.
Some architects indicate on a drawing where
it is permissible to make a joint when the concrete
placement is terminated at the end of the day.
If no indication is given, the project engineer or
architect must approve the location.
Foundation
Waterproofi ng
Waterproofi ng of foundation walls is
needed in areas where soil and climatic con-
ditions demand protection from underground
water. Residential waterproofi ng can be done
with a variety of materials, but usually consists
of mopping the outside of the foundation wall
with tar or asphalt, Figure 10-15. Sometimes,
a polyethylene sheet is applied over the tar.
Drawings for a foundation to be waterproofed
will have a heavy black line on the exterior wall
with a note indicating location. Also, the build-
ing specifi cations may specify the exact mate-
rial and process to be used.
A layer of crushed rock or gravel is laid below
the fl oor area. This layer is then covered with a
heavy plastic vapor barrier to keep the dampness
in the ground from transferring to the slab and
into the building.
Other features are used in concrete con-
struction to protect the building from water
seepage. To inhibit water transmission at con-
struction joints, a special sealing device called
a waterstop is used. A waterstop is a linear sec-
tion of PVC located in the concrete to serve as
a moisture barrier. In Figure 10-16, a waterstop
is used where the footing and foundation wall
intersect at the keyway.
1/2" expansion joint
Rigid insulation
Gravel
SECTION VIEW
Figure 10-14.
An expansion joint made of a fl exible
material is placed between the concrete slab and wall.
Figure 10-15.
Tar being applied to a residential
foundation wall for waterproofi ng.