Wall forms are made up of five basic parts. They are as follows:
(1) sheathing, to shape and retain the concrete until it sets;
(2) studs, to form a framework and support the sheathing; (3)
wales, to keep the form aligned and support the studs; (4) braces,
to hold the forms erect under lateral pressure; and (5) ties and
spreaders or tie-spreader units, to hold the sides of the forms
at the correct spacing (fig. 7-29).
Wall forms may be built in place or pre-fabricated, depending
on the shape and the desirability for reuse.
Wall forms are usually reinforced against displacement
by the use of TIES.
Figure 7-29. - Parts of a typical wall
Figure 7-30. - Wire ties for wall
Figure 7-31. - Snap tie forms
Two types of simple wire ties, used with wood SPREADERS,
are shown in figure 7-30. The wire is passed around the studs
and wales and through small holes bored in the sheathing. The
spreader is placed as close as possible to the studs, and the
tie is set taut by the wedge shown in the upper view or by twisting
with a small toggle, as shown in the lower view. When the concrete
reaches the level of the spreader, the spreader is knocked out
and removed. The parts of the wire that are inside the forms remain
in the concrete; the outside surplus is cut off after the forms
Wire ties and wooden spreaders have been largely replaced by
various manufactured devices that combine the functions of the
tie and spreader. Figure 7-31 shows one of these, called a SNAP
TIE. These ties are made in various sizes to fit various wall
thickness. The tie holders can be removed from the tie rod. The
rod goes through small holes bored in the sheathing and also through
the wales, which are usually doubled for that purpose. Tapping
the tie holders down on the ends of the rod brings the sheathing
to bear solidly against the spreader washers. After the concrete
has hardened, the tie holders can be detached to strip the forms.
After the forms are stripped, a special wrench is used to break
off the outer sections of rod; they break off at the breaking
points, located about 1 in. inside the surface of the concrete.
Small surface holes remain, which can be plugged with grout, if
Another type of wall form tie is the TIE ROD, as
shown in figure 7-32. The rod in this type consists of three sections:
an inner section, which is threaded on both ends, and two threaded
outer sections. The inner section, with the cones set to the thickness
of the wall, is placed between the forms, and the outer sections
are passed through the wales and sheathing and threaded into the
cone nuts. The clamps are then threaded up on the outer sections
to bring the forms to bear against the cone nuts. After the concrete
hardens, the clamps are loosened, and the outer sections of rod
are removed by threading them out of the cone nuts.
Figure 7-32. - Tie rod
Figure 7-33. - Method of joining wall form panels at a
After the forms are stripped, the cone nuts are removed from the
concrete by threading them off the inner sections of rod with
a special wrench leaving the cone-shaped surface holes. The outer
sections and the cone nuts may be reused indefinitely.
The use of prefabricated panels for form work has recently been
on the increase. These panels can be reused many times, thus reducing
the time and labor required for erecting forms on the site.
Foundation Walls: A very good rule to
fix the thickness of rubble-stone foundation walls is, that they
shall be at least 8 inches thicker than the wall next above them,
for a depth of 12 feet below grade or curb level; and they should
be increased 4 inches in thickness below that point, for every
additional 10 feet or less in depth. Thus, if the first story
walls are 12 inches thick, the stone foundation walls would have
to be 20 inches thick for 12 feet in depth, and 24 inches thick
below that point for 10 feet or less. Rubble-stone foundations
walls are seldom made less than 18 inches in thickness. A wall
18 inches thick is not always needed to carry the superimposed
weight, but smaller walls are more expensive to build consequently
are seldom constructed.
The thickness of foundation walls in all the large cities is
controlled by the building laws. Where there are no existing laws,
Table 1 will serve as a guide.
Stone Walls: The laws regarding the
thickness of stone walls differ in the various cities, and no
uniform rules can be given. For ashlar work, the New york law
states that "where walls or piers are built of coursed stones,
with dressed level beds and vertical joints the Department of
Buildings shall have the right to allow such walls or piers to
be built of less thickness than specified for brickwork, but in
no case shall said walls or piers be less than three-quarters
of the thickness provided fro brickwork."
The following regulations apply to the District of Columbia for
rubble work: "Walls laid with rubble work shall be one fourth
thicker than required for brick walls, but never less than 18
inches thick; they must be constructed with flat stone, sound
and durable, laid on their natural beds, and brought to a level
every 3 feet in height. They must be built between two lines,
shall have bond stone or headers extending through the thickness
of the walls at intervals not exceeding 3 feet, and shall be laid
in cement mortar composed of 2 parts sand and 1 part of cement.
No rubble wall shall be located as a party wall unless the written
consent of the adjoining owner shall first be filed in the office
of the Inspector of Buildings. The restriction as to location
of the party wall above mentioned shall not apply to stone foundation
walls which support brick walls."
For ashlar facing, the requirements for the District of Columbia
are as follows: " Thin ashlar facing shall not be counted
ted in determining the thickness of walls. If stone facing is
used with bond courses alternately, not less than 8 inches thick,
on the beds, the n such facing shall be counted as forming part
of the wall, and the total thickness of the wall and facing shall
not be required to be more than that herein specified for walls
(meaning brick) but never less than 13 inches thick." that
way. Nail your 2x6 down all the way around, along the chalk line.
You are now ready to start the forming of the wall itself.
Form work for your forms should be 3/4" plywood. This will
come in 4'x8' sheets with no holes for ties. You will need to
drill holes in all the sheets for the ties to go through. The
ties will hold both sides of the form work together at a set dimension
while you pour the concrete. Typically, I will drill holes at
16" on center and start 8" in from each side. After
drilling you will begin at a corner and nail the bottom of the
plywood to the 2x6 "sill plate" with 8d box nails or
roofing nails. Do the two pieces on each side of the corner first
and nail the tops together, which will insure it doesn't fall
over while you are putting up the next piece.
After you get the outside of the form up you will start installing
your vertical and horizontal rebar. Start with your 3'-9"
vertical #4's by tying them to the stubs we talked about in the
Concrete Footing article. After this is complete install the horizontal
#4's. On a typical 4' tall wall you should have 3-4 rows, of which
the first will be about 3-6 inches from the top and the bottom
one about 10-12 inches from the footing. Make sure to wrap the
corners and not just dead end it, and also to overlap each new
piece at least 12 times the diameter of the bar.
Before you start on the inside form you will need to "Stuff
Ties" on the outside form. For this operation you will need
to purchase ties that will hold the inside and outside form at
the correct distance apart. These ties will need to be placed
in the holes talked about earlier and 2 - 2x4s (whaler) placed
on the outside with a locking cam to hold it in place (you will
probably need to rent the cams or borrow from someone). Now that
you have all the ties stuffed you can begin to hang your inside
form. You will probably need to rip 8" off the inside corner
form to line up with the outside form tie holes. As before, start
at a corner and work around the foundation. After the inside form
is set go back again and install your whalers and cams.
NOTE: What is described above is a typical
method of forming a stem wall. Make sure to pre-plan everything.
Did you make the wall a length that is divisible by 4? If not,
where are you going to put the filler, and will the tie holes
line up? How much do you need to rip off the ends to start a corner?
Pre-made forms come in a dozen different varieties and each has
it's own benefits and problems. When selecting forms talk to your
local concrete rental store to see what would be best for you.
Pre built forms are fairly easy to set. The same principles apply
as the plywood forms, except that you will probably have fillers
for most typical widths and pre made corners. Your concrete rental
store should have installation directions and can answer questions.
I would go into more detail but there are so many different systems
that it wouldn't be very beneficial. Just remember - PREPLAN.
The last thing to do for your form work is plumb it and square
the top. Again start at a corner and plumb the corner with a 4'
level. Have some 2x4's and form stakes nearby. When you determine
where the wall needs to go place your 2x4 bracing accordingly.
Nail it to the top whaler and place a form stake a distance away
that will allow you to nail the stake to the 2x4 bracing. Push
and pull the wall until it is plumb and square.You are now ready
to install your screed strip. A screed strip is a reference line
that you can't miss when pouring concrete made of 1/4" x
3/4" pine or something similar. Use a builders level or a
laser level to put a line around the entire inside form at finished
concrete height. Nail the top of the screed strip at this line.
I suggest putting it to the inside form so that it won't show
after stripping and backfilling. Now when you pour the concrete
you will have a good reference of exactly where to finish to.
Pour the concrete and finish the top level with the screed strip.
After finishing the top of the wall place your anchor bolts 6"
from each corner and 3' on center around the wall. Some say that
4' is good enough and it probably is, but I usually go with 3'
or sometimes less. The anchor bolts will be used later to hole
your sill plate down.
Stripping your forms is a simple task that involves popping the
cams off and stripping the whalers off. Then strip the plywood
or pre built forms off and break your ties off. If the wall will
be exposed you can patch the tie holes back in later. Now strip
your footing form work
The last thing you will need to do is waterproof the wall. This
can be a pain, but is a necessary step. There are many different
types of waterproofing materials; ask your local home building
center what they recommend.