Concrete 111for 100 cy in about one to two labor hours, depending on the
type of heater and fuel being used. Fuel and equipment costs
are also based on the type used.
If approximately 100,000 BTUH are required per 300 to
400 sf (averaging a height of 8 feet), estimate the number of
units needed (depending on the net output of the unit) and
determine the amount of fuel that will be consumed per
hour, the number of hours the job will require, and the
equipment and fuel costs.
The continuous spray requires the purchase of equip-
ment (which is reusable) and the employment of labor to set
it up. It will require between one-half and one labor hour to
run the hoses and set up the equipment for an area of 100 sf.
The equipment should be taken down and stored when it is
not in use.
Moisture-retaining and watertight covers are estimated by
the square footage of the surface to be covered and separated
into slabs or walls and beams. The initial cost of the materials is
estimated and is divided by the number of uses expected of
them. Covers over slabs may be placed at the rate of 1,000 sf per
one to three labor hours, and as many as five uses of the mate-
rial can be expected (except in the case of canvas, which lasts
much longer); wall and beam covers may be placed at the rate
of 1,000 sf per two to six labor hours. The sealing of watertight
covers takes from three-quarters to one labor hour per 100 lf.
Sealing compounds are estimated by the number of
square feet to be covered divided by the coverage (in square
feet) per gallon to determine the number of gallons
required. Note whether one or two coats are required. If the
two-coat application is to be used, be certain to allow for
material to do both coats. For two-coat applications, the first
coat coverage varies from 200 to 500 sf, while the second coat
coverage varies from 350 to 650 sf. However, always check
the manufacturer’s recommendations. Equipment required
will vary according to the job size. Small areas may demand
the use of only a paint roller, while medium-size areas may
require a pressure-type hand tank or backpack sprayer.
Large, expansive areas can best be covered with special
mobile equipment. Except for the roller, the equipment has
much reuse, usually a life expectancy of five to eight years
with reasonable care. The cost of the equipment is spread
over the time of its estimated usage. Using the pressure-type
sprayer, the estimator figures from one and one-half to three
hours will be required per 100 sf. In estimating labor for
mobile equipment, the estimator should depend more on the
methods in which the equipment is mobilized than on any-
thing else, but labor costs can usually be cut by 50 to 80 percent
if mobile equipment is used.
Specifications. The requirements of the architect/
engineer regarding curing of the concrete are spelled out in
the specifications. Sometimes they detail almost exactly what
must be done for each situation, but often they simply state
that the concrete must be kept at a certain temperature for a
given number of days. The responsibility of protecting the
concrete during the curing period is that of the general con-
tractor (who may in turn delegate it to a subcontractor).
10–8 Transporting Concrete
The methods used to transport the concrete from its point of
delivery by the ready-mix trucks or the field-batching plant
include truck chutes, buggies (with and without power),
crane and bucket, crane and hoppers, tower and buggies,
forklifts, conveyors, and pumps. Several combinations of
methods are available, and no one system is the answer. It is
likely that several methods will be used on any one project.
Selection of the transporting method depends on the type of
pour (floor, wall, curb, etc.), the total volume to be poured in
each phase (in cubic yards), the distance above or below
grade, equipment already owned, equipment available, the
distance from the point of delivery to the point of use, and
possible methods of getting the concrete to that point.
Once a decision on the method of transporting the con-
crete has been made, the cost of equipment must be deter-
mined, as well as the anticipated amount of transporting
that can be done using that equipment and a given crew of
workers. From these, the cost of transporting the concrete
may be estimated. Generally speaking, the higher the build-
ing and the further the point of use from the point of deliv-
ery, the more expensive the cost of transporting.10–9 Forms
This portion of the chapter is not a course in form design,
but identifies the factors involved in formwork relative to
costs. No one design or system will work for all types of
formwork. In general, the formwork must be true to grade
and alignment, braced against displacement, resistant to all
vertical and horizontal loads, resistant to leaking through
tight joints, and of a surface finish that produces the desired
texture. The pressure on the forms is the biggest considera-
tion in the actual design of the forms.
In the design of wall and column forms, the two most
important factors are the rate of placement of the concrete
(feet per hour) and the temperature of the concrete in the
forms. From these two variables, the lateral pressure (psf )
may be determined. Floor slab forms are governed primarily
by the actual live and dead loads that will be carried.
Actual construction field experience is a big factor in
visualizing exactly what is required in forming and should
help in the selection of the form type to be used. The types of
forms, form liners, supports, and methods are many; prelim-
inary selections must be made during the bidding period.
This is one of the phases in which the proposed job superin-
tendent should be included in the discussions of the meth-
ods and types of forms being considered, as well as in the
consideration of what extra equipment and work power may
be required.
Engineering data relative to forms and the design of
forms are available from the American Concrete Institute
(ACI), Portland Cement Association (PCA), and most man-
ufacturers. These reference manuals should definitely be
included in the estimator’s reference library.