Figure 7-52.-Curing a wall with wet burlap
METHODS THAT PREVENT MOISTURE
LOSS. Methods that prevent moisture loss include
laying waterproof paper, plastic film, or liquid-
membrane-forming compounds, and simply leaving
forms in place. All prevent moisture loss by sealing
Waterproof paper (figure 7-53) can be used to cure
horizontal surfaces and structural concrete having
relatively simple shapes. The paper should be large
enough to cover both the surfaces and the edges of
the concrete. Wet the surface with a fine water spray
before covering. Lap adjacent sheets 12 inches
Figure 7-53.-Waterproof paper used for curing.
or more and weigh their edges down to form a
continuous cover with closed joints. Leave the
coverings in place during the entire curing period.
Plastic film materials are sometimes used to cure
concrete. They provide lightweight, effective moisture
barriers that are easy to apply to either simple or
complex shapes. However, some thin plastic sheets
may discolor hardened concrete, especially if the
surface was steel-troweled to a hard finish. The
coverage, overlap, weighing down of edges, and
surface wetting requirements of plastic film are
similar to those of waterproof paper.
Curing compounds are suitable not only for curing
fresh concrete, but to further cure concrete following
form removal or initial moist curing. You can apply
them with spray equipment, such as hand-operated
pressure sprayers, to odd slab widths or shapes of
fresh concrete, and to exposed concrete surfaces
following form removal. If there is heavy rain within
3 hours of application, you must respray the surface.
You can use brushes to apply curing compound to
formed surfaces, but do not use brushes on unformed
concrete because of the risk of marring the surface,
opening the surface to too much compound
penetration, and breaking the surface film continuity.
These compounds permit curing to continue for long
periods while the concrete is in use. Because curing
compounds can prevent a bond from forming between
hardened and fresh concrete, do not use them if a
bond is necessary.
Forms provide adequate protection against moisture
loss if you keep the exposed concrete surfaces wet.
Keep wood forms moist by sprinkling, especially
during hot, dry weather.
Forms should, whenever possible, be left in place
for the entire curing period. Since earl y form
removal is desirable for their reuse, a reliable basis
for determining the earliest possible stripping time is
necessary. Some of the early signs to look for during
stripping are no excessive deflection or distortion and
no evidence of cracking or other damage to the
concrete due to the removal of the forms or the form
supports. In any event, forms must not be stripped
until the concrete has hardened enough to hold its
own weight and any other weight it may be carrying.
The surface must be hard enough to remain
undamaged and unmarked when reasonable care is
used in stripping the forms.