175THERMAL AND MOISTURE PROTECTION
CHAPTER FOURTEEN
14–1 Waterproofing
Waterproofing is designed to resist the passage of water and,
usually, to resist the hydrostatic pressures to which a wall or
floor might be subjected. (Dampproofing resists dampness,
but it is not designed to resist water pressure.) Waterproofing
can be effected by the admixture mixed with the concrete,
membrane waterproofing;by placing layers of waterproofing
materials on the surface, the integral method;and by the
metallic method.
14–2 Membrane Waterproofing
Membrane waterproofing (Figure 14.1) consists of a buildup
of tar or asphalt and membranes (plies) into a strong imper-
meable blanket. This is the only method of waterproofing
that is dependable against hydrostatic head. In floors, the
floor waterproofing must be protected against any expected
upward thrust from hydrostatic pressure.
The actual waterproofing is provided by an amount of tar
or asphalt applied between the plies of reinforcement. The
purpose of the plies of reinforcement is to build up the amount
of tar or asphalt that meets the waterproofing requirements
and to provide strength and flexibility to the membrane.
Reinforcement plies are of several types, including a
woven glass fabric with an open mesh, saturated cotton fiber,
and tarred felts.
Newly applied waterproofing protection membranes
should always be protected against rupture and puncture
during construction and backfilling. Materials applied over
the membrane include building board and rigid insulation
for protection on exterior walls against damage during con-
struction and backfilling.
Another type of waterproofing is the use of sprayed-on
asphalt with chopped fiberglass sprayed on simultaneously.
The fiberglass reinforcement helps the resultant film bridge
hairline cracks that may occur in the wall. The sprayed-on
waterproofing requires that one to two days of good weather
pass before backfilling can begin. Take care during backfill so
that the film is not damaged.Estimating Membrane Waterproofing. The unit of
measurement is the square (1 square 100 sf ). To estimate
the quantity of reinforcement felt required, the estimator
determines the square footage of the walls and floors that
require membrane waterproofing and keeps walls and floors
separate.
The specifications must be checked to determine the
number of membrane (plies) required, the kind and weight
of reinforcement ply, the number of coatings, the type of
coating (tar or asphalt), and the pounds of coating material
required to complete each 100 sf of waterproofing. The esti-
mator also checks to determine what industry requirements
must be met and whether the specifications limit the manu-
facturer’s materials that may be used.
If one layer of reinforcement is specified, the amount
must allow for laps over the footings and at the top of the
wall, as well as the lap required over each strip of reinforce-
ment. A 4-inch side lap of layers plus the top and bottom
laps will require about 20 percent additional. A 6-inch lap
will require about 25 percent additional to the area being
waterproofed. Lap is generally listed in the specifications.
The number of plies used usually ranges from two to five,
and the amount to be added for laps and extra material
drops to about 10 percent of the actual wall or floor area.
Most felt and cotton fabric reinforcement is available in
rolls of 432 sf. Glass yarn reinforcement is generally avail-
able in rolls of 450 sf. Different manufacturers may have
various size rolls and sheets available of certain types of
reinforcements.
The amount of tar required varies depending on the
number of plies; the amount used per square (one square
100 sf ) should be in the specifications. Figure 14.2 shows
the amount of reinforcing and coating required. Membrane
waterproofing is similar to applying built-up roofing, but