Formed FinishesWhen form release ag

Formed Finishes
When form release agents are over
applied, they form a film that varies in
thickness as excess release agent is dislocated
during concrete placement and
vibration. In the worst case, cement paste
and color pigment can "float" in pockets
of excess release agent and produce
uneven coloring. This also can produce a
weak concrete surface, bug holes, small
voids, and other visual defects (see Photo
16). Oil-based form coatings should be
avoided as they may stain the concrete.
Reputable manufacturers can provide
information on recent developments in
The Construction Specifier December 1998
13. Over troweling can entrap moisture
and create dark areas.
14. Edging work, performed after the concrete began
to harden, is the likely cause of this discoloration.
15. The pale broom mark, which is permanent,
shows the first broom stroke after the broom
was wetted.
16. Excessive use of form release agents can
contribute to discoloration and voids in a
formed concrete surface.release agent technology that have
improved as-cast surface uniformity.
When concrete is cast against clean,
smooth-surface form materials such as
steel or plastic-faced plywood, the as-cast
concrete surface will be smooth and shiny.
While a rough concrete surface will scatter
reflected light and soften the impact of
blemishes, a smooth surface will make
variations more conspicuous. Most castin-place
and tilt-up concrete is textured
for this reason. A variety of textured form
liners are available and can be used to create
attractive architectural effects.
Another alternative is to use mechanical
methods such as sandblasting, grinding,
or bush hammering to roughen the
surface. Discolorations caused by interaction
with the form release is typically only
"skin deep" and can be removed using
these mechanical abrasion techniques (see
Photos 17 and 18). Removing additional
cement provides an exposed aggregate finish,
as discussed above. Many attractive
surface treatments can be created by combining
a colored concrete matrix with
select aggregate in complimentary or contrasting
hues.
Porous form materials, such as lumber