Building Poured-Concrete Homes, continued
Wall form erection actually begins in the front office with a
CAD-generated plan that details the size and placement of every
form panel in the wall system. The crew snaps offset wall lines
and carefully checks the spans and diagonals for square and
parallel. The slabs are generally poured quite level and
reasonably square. If we do run into a dimensional discrepancy,
we can make adjustments of up to 2 inches without serious
problems. But because the roof trusses rest directly on our
walls, the layout must be as square, parallel, and accurate as
Most forming systems are based on a 2-foot module; we use a
3-foot modular aluminum form system (Precise Forms,
800/537-0706, www.preciseforms.com), which effectively
reduces erection time by about 33%. Using this system, we can
start setting panels for a full house at 7:00 a.m. and be ready
to pour by 10:00 a.m.
The panels are held together by a series of captive pins that
also engage the wall ties. The ties are flat 10-inch-long steel
straps with a hole at each end. The pins pass through the tie
holes and connect to the next form in line (Figure 5).
Figure 5.Attached captive pins are affixed to the
face of each aluminum form on 12-inch centers. The pins pass
through flat steel snap-ties before engaging the next form in
line. Adjustable guide-ties enable proprietary window bucks to
hang on the pins, automatically leveling the bucks in the
The panels are spaced for a 6-inch-thick wall. The outside
forms rest on the slab sub's dimensional lumber forms, and the
interior forms are set parallel to the offset lines.
At the bottom of the form, a plastic clip gets anchored to the
slab with a hand-driven masonry nail to prevent movement during
the pour. The clip removes easily during form stripping.
Window bucks. The aluminum
bucks we use to block out the window openings are made to fit a
variety of typical windows, aluminum or vinyl clad. The bucks
have adjustable tie guides that hang on the captive pins and
hold the buck level inside the forms. The guides are set to
allow for a standard 16-inch-deep concrete header. The buck
forms a flared exterior opening and a 7/8-inch stop, recessed
about 2 inches in from the interior face. This allows the
windows to be installed from the outside, bedded in caulk
against the stop (Figure 6).
Figure 6.Windows are installed from the outside of
the wall and are pressed into a continuous bead of silicone
sealant against a 7/8-inch offset lip cast in the opening. The
installation tolerance is tight, typically only about 1/4 inch
over the unit dimension, to minimize air infiltration around
After the forms are set, braced, and leveled, they're ready
for pumping. We use a 3,000-psi concrete mix with 3/8-inch
aggregate — limestone in our neck of the woods.
Pumping can empty a 10-cubic-yard truck in 15 minutes. The
average house takes 30 yards of concrete, so we schedule the
trucks to arrive at 15-minute intervals. Even so, we take about
1 1/2 to 2 hours to pump a typical house. We use a "Super-P"
mix containing water reducers and plasticizers, which flows
well around the bucks and eliminates the need for vibrating.
The forms are filled to the top and allowed to mound for about
10 minutes before striking off. The forms are of precise,
uniform height and leveled on the slab, making the top of the
wall automatically level.
With a block wall, the framers grout their own steel truss
anchors, but we wet-set them. We generally use USP TA-22
(22-inch) wall-to-truss connectors (Figure 7). Truss anchors
wrap over the top chord and are nailed in accordance with the
manufacturer's recommended requirements. The anchors have to be
accurately set to work with the 2-foot-on-center truss layout;
we're allowed only an 1/8-inch tolerance. We set the anchors
according to a layout plan created using MiTek 4.2 truss layout
software (MiTek, 314/434-1200,
www.mitekinc.com). The anchors are embedded
4 to 6 inches into the top of the wall. We have to replace any
off-layout anchors with Tapcon-fastened ties, so we try hard to
avoid layout errors.
Truss anchors must be
accurately placed in the wet concrete, within 1/8 inch of the
truss location to perform as designed. The anchor is embedded 4
to 6 inches into the concrete and wrapped over the top of the
truss, then nailed. The anchors are rated to resist 120 mph
We can safely strip forms the day after the pour, when the
concrete has reached 50% of its design strength. (Concrete
reaches full design strength in 28 to 45 days.) The stripping
crew removes the pins, strips the forms, and stacks them in
special vertical transportation baskets. The wall tie
protrusions snap off with a sideways hammer blow. If they're
too high to reach, we use an 8-foot stud (Figure 8). The
stripping crew polices the site and cleans excess concrete from
the slab, leaving it ready for the framing crew. This ends our
company's involvement in the house, and we move on to the next
Figure 8.Wall ties snap on impact; those out of
easy hammer reach fall to a length of 2x4. The forming crew
leaves the slab broom-clean for the framers.
Over the next few days, the framers set the trusses, sheathe
and shingle the roof, and stand the interior partitions.
Foil-faced 3/4-inch-thick rigid foam paneling is applied to the
inside face of the concrete walls and held in place with
vertical 1x3 furring strips, 2 feet on-center, nailed to the
concrete with powder-actuated fasteners (Figure 9). The
electrician cuts the foam away to set 1 1/2-inch-deep outlet
boxes directly against the concrete, using a powder-actuated
Figure 9.Foil-faced 3/4-inch-thick
polyisocyanurate foam board is nailed to the interior wall
surface and strapped on 2-foot centers with vertical 1x3
furring strips to receive the drywall. The furring and
electrical boxes are nailed to the wall with PAFs.
Interior partitions are typically framed with light-gauge
steel studs, continuing the termite-resistant construction.
Occasionally, SPF 2x4s are used, stood on a bottom plate of
The exterior finish is a one-coat colored stucco skimmed over
a bonding agent and textured (Figure 10).
Figure 10.One-coat stucco and standardized
decorative detailing provide a simple, attractive, and durable
Because concrete continues to cure for several weeks, we wait
30 to 45 days before bringing in the stucco crew. This delay
minimizes the telegraphing of any shrinkage cracks through the
stucco finish. Though infrequent and typically only hairline,
these cracks are normal. If a crack does appear through the
stucco finish, it gets repaired with colorized caulk.Vince Heuseris a field manager for Solid Wall Systems
in Cocoa, Fla. Thanks to Robert Wiebel, a technical consultant
to SWS, who helped with this article.