absorption with porous materials such as burlap. During finishing
operations, extreme care shall be taken to prevent over finishing or
working water into the surface; this can cause "crazing" (surface shrinkage
cracks which appear after hardening) of the surface. Any slabs with
surfaces which exhibit significant crazing shall be removed and replaced.
During finishing operations, surfaces shall be checked with a 10 foot
straightedge, applied in both directions at regular intervals while the
concrete is still plastic, to detect high or low areas.
3.12.2
Rough Slab Finish
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NOTE: Rough-slab finish alone is used when a bonded
surface course for heavy use industrial floor is
specified, or where roof fill or thick mortar
setting bed is used. If the drawings do not
indicate the slabs to receive only a rough slab
finish, they must be specified here. Rough slab
finish must be retained as the first operation for
all subsequent finishing.
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As a first finishing operation for unformed surfaces and as final finish
for slabs to receive mortar setting beds, the surface shall receive a rough
slab finish prepared as follows. [Areas indicated on the drawings] [The
following areas [_____]] shall receive only a rough slab finish. The
concrete shall be uniformly placed across the slab area, consolidated as
previously specified, and then screeded with straightedge strikeoffs
immediately after consolidation to bring the surface to the required finish
level with no coarse aggregate visible. Side forms and screed rails shall
be provided, rigidly supported, and set to exact line and grade. Allowable
tolerances for finished surfaces apply only to the hardened concrete, not
to forms or screed rails. Forms and screed rails shall be set true to line
and grade. "Wet screeds" shall not be used.
3.12.3
Floated Finish
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NOTE: If the drawings do not indicate the areas to
receive a floated finish, they must be specified
here.
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Slabs to receive more than a rough slab finish shall next be given a wood
float finish. [Areas as indicated on the drawings] [The following areas
[_____]] shall be given only a float finish. The screeding shall be
followed immediately by darbying or bull floating before bleeding water is
present, to bring the surface to a true, even plane. Then, after the
concrete has stiffened so that it will withstand a man's weight without
imprint of more than 6 mm 1/4 inch and the water sheen has disappeared, it
shall be floated to a true and even plane free of ridges. Floating shall
be performed by use of suitable hand floats or power driven equipment.
Sufficient pressure shall be used on the floats to bring a film of moisture
to the surface. Hand floats shall be made of wood, magnesium, or aluminum.
Lightweight concrete or concrete that exhibits stickiness shall be floated
with a magnesium float. Care shall be taken to prevent over-finishing or
incorporating water into the surface.
SECTION 03300A
Page 53
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