112 CHAPTER TEN
The forms for concrete footings, foundations, retaining
walls, and floors are estimated by the area (in square feet) of
the concrete that comes in contact with the form. The plans
should be studied carefully to determine whether it is possi-
ble to reuse the form lumber on the building and the num-
ber of times it may be reused. It may be possible to use the
entire form on a repetitive pour item, or the form may have
to be taken apart and reworked into a new form.
On higher buildings (eight stories and more), the cost of
forms may be reduced and the speed of construction may be
increased if high early strength cements are used instead of
ordinary portland cement. The forms could then be stripped
in 2 or 3 days instead of the usual 7 to 10 days; however, not
all architect/engineers will permit this.
Many types of forms and form liners may be rented.
The rental firms often provide engineering services as well as
the forms themselves. Often the cost of the forms required
for the concrete work can be reduced substantially.
Wood Forms. Wood is one of the most common materi-
als used to build forms. The advantages of wood are that it is
readily accessible and easy to work with, and that once used,
it may be taken apart and reworked into other shapes. Once
it has been decided to use wood, the estimator must deter-
mine the quantity of lumber required and the number of
uses. This means the construction of the forms must be
decided upon with regard to plywood sheathing, wales, studs
or joists, bracing, and ties. The estimator can easily deter-
mine all of this if the height of the fresh concrete pour (for
columns and walls), the temperature of the placed concrete,
and the thickness of the slab (for floors) are known. The
manufacturer’s brochures or ACI formwork engineering
data may be used.
Metal Forms. Prebuilt systems of metal forms are used
extensively on poured concrete not only on large projects,
but even for foundation walls in homes. Advantages are that
these systems are reusable several times, easily adaptable to
the various required shapes, interchangeable, and require a
minimum of hardware and a minimum of wales and ties,
which are easily placed. They may be purchased or rented,
and several timesaving methods are employed. Curved and
battered weights are easily obtained, and while the plastic-
coated plywood face liner is most commonly used, other lin-
ers are available. Heavy-duty forms are available for heavy
construction jobs in which a high rate of placement is
desired.
Engineering data and other information pertaining to
the uses of steel forms should be obtained from the metal
form supplier. The supplier can give information regarding
costs (rental and purchase), tie spacing, the number of forms
required for the project, and the labor requirements.
Miscellaneous Forms. Column forms are available in
steel and laminated plies of fiber for round, square, and rectan-
gular columns. Many manufacturers will design custom forms
of steel, fiber, and fiberglass to meet project requirements.
These would include tapered, fluted, triangular, and half-
rounded shapes. Fiber tubes are available to form voids in cast-
in-place (or precast) concrete; various sizes are available. Most
of these forms are sold by the linear footage required of a given
size. The fiber forms are not reusable, but the steel forms may
be used repeatedly.Estimate. The unit of measurement used for forms is the
actual contact area (in square feet) of the concrete against
the forms (with the exception of moldings, cornices, sills,
and copings, which are taken off by the linear foot). The
forms required throughout the project must be listed and
described separately. There should be no deductions in the
area for openings of less than 30 sf.
Materials in the estimate should include everything
required for the construction of the forms except stagings
and bridging. Materials that should appear are struts, posts,
bracing, bolts, wire, ties, form liners (unless they are special),
and equipment for repairing, cleaning, oiling, and removing.
Items affecting the cost of concrete wall forms are the
height of the wall (since the higher the wall, the more lumber
that will be required per square foot of contact surface) and
the shape of the building, including pilasters.
Items affecting the cost of concrete floor forms include
the floor-to-floor height, reusability of the forms, length of
time the forms must stay in place, type of shoring and sup-
ports used, and the number of drop beams required.
The various possibilities of renting or purchasing forms,
using gang forms built on ground and lifted into place, slip
forming, and so on should be considered during this phase.
Although approximate quantities of materials are given
(Figure 10.31) for wood forms, a complete takeoff of materi-
als should be made. The information contained in Fig-
ure 10.31 is approximate and should be used only as a check.
In addition, Figure 10.32 is a guideline of the labor produc-
tivity to build different configurations of formwork.Estimating Wood Footing Forms. The estimator
must first determine whether the entire footing will be
poured at one time or whether it will be poured in segments,
which would permit the reuse of forms.Labor Hours
Type of Lumber Strip &
Form fbm Assemble Erect Clean Repair
Footings 200–400 2–6 2–4 2–5 1–4
Walls 200–300 6–12 3–6 1–3 2–4
Floors 170–300 2–12 2–5 1–3 2–5
Columns 170–350 3–7 2–6 2–4 2–4
Beams 250–700 3–8 3–5 2–4 2–4
Stairs 300–800 8–14 3–8 2–4 3–6
Moldings 170–700 4–14 3–8 2–6 3–6
Sill, Coping150–600 3–12 2–6 2–4 2–6
fbmFoot Board MeasureFIGURE 10.31.Wood Forms, Approximate Quantity of
Materials, and Labor Hours.