Begin floating immediately after screeding while
the concrete is still plastic and workable. However,
do not overwork the concrete while it is still plastic
because you may bring an excess of water and paste to
the surface. This fine material forms a thin, weak
layer that will scale or quickly wear off under use. To
remove a coarse texture as the final finish, you usually
have to float the surface a second time after it partially
As the sheen of water begins to leave the surface,
edging should begin. All edges of a slab that do not
abut another structure should be finished with an
edger (figure 7-48). An edger dresses corners and
rounds or bevels the concrete edges. Edging the slab
helps prevent chipping at the corners and helps give
the slab a finished appearance.
If a dense, smooth finish is desired, floating must
be followed by steel troweling (figure 7-49).
Troweling should begin after the moisture film or
sheen disappears from the floated surface and when
the concrete has hardened enough to prevent fine
material and water from being worked to the surface.
This step should be delayed as long as possible.
Troweling too early tends to produce crazing and lack
of durability. However, too long a delay in troweling
results in a surface too hard to finish properly. The
usual tendency is to start to trowel too soon.
Troweling should leave the surface smooth, even, and
free of marks and ripples. Spreading dry cement on a
wet surface to take up excess water is not a good
practice where a wear-resistant and durable surface is
Figure 7-49.-Steel finishing tools and troweling operations.
required. Wet spots must be avoided if possible.
When they do occur, however, finishing operations
should not be resumed until the water has been
absorbed, has evaporated, or has been mopped up.
An unslippery, fine-textured surface can be
obtained by troweling lightly over the surface with a
circular motion immediately after the first regular
troweling. In this process, the trowel is kept flat on
the surface of the concrete. Where a hard
steel-troweled finish is required, follow the first
regular troweling by a second troweling. The second
troweling should begin after the concrete has become
hard enough so that no mortar adheres to the trowel,
and a ringing sound is produced as the trowel passes
over the surface. During this final troweling, the
trowel should be tilted slightly and heavy pressure
exerted to thoroughly compact the surface. Hairline
cracks are usually due to a concentration of water and
extremely fine aggregates at the surface. his results
from overworking the concrete during finishing
operations. Such cracking is aggravated by drying
and cooling too rapidly. Checks that develop before
troweling can usually be closed by pounding the
concrete with a hand float.