Formwork for Concrete Structures by R.L.Peurifoy and G.D- By EasyEngineering.net

74 Chapter Four
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Form Liners
Designers of architectural concrete frequently specify a particular finish
on the surface of the concrete. Special surface finishes can be achieved
by attaching form liners to the inside faces of forms. The form liners can
be used to achieve an extremely smooth surface, or to achieve a particular
textured finish on the concrete surface. For example, for walls the
texture may simulate a pattern of bricks or natural grains of wood. A
variety of types and shapes of form liners are available to produce the
desired finish on the concrete surface.
There are various types of materials that may be suitable as form liners,
depending on the desired finish. This includes plywood, hardboard,
coatings, and plastics. Liners may be attached to the sides of forms with
screws, staples, or nails. In some situations, the liners may be attached
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with an adhesive that bonds the liner to the steel or wood forms.
Plastic liners may be flexible or rigid. A rubberlike plastic that is
made of urethanes is flexible enough that it can be peeled away from
the concrete surface, revealing the desired texture. Polyvinyl chloride
(PVC) sheets are rigid with sufficient stiffness for self-support. The
sheets are available in 10-ft lengths. A releasing agent should be applied
to the form liner to ensure uniformity of the concrete surface and to
protect the form liner for possible reuse.
Nails
There are three types of nails that are normally used in formwork:
common wire nails, box nails, and double-headed nails. Common
wire nails are used for attaching formwork members or panels for
multiple uses, when nails are not required to be removed in stripping
the forms. The common wire nail is the most frequently used nail for
fastening form members together. A box nail has a thinner shank and
head than a common wire nail, which makes it more useful for builtin-place
forms. Box nails pull loose more easily than common or doubleheaded
nails.
Double-headed nails are frequently used in formwork when it is
desirable to remove the nail easily, such as for stripping forms. The
first head permits the nail to be driven fully into the wood; the shaft
of the nail extends a fraction of an inch beyond the first head to a
second head. This head, protruding slightly outside the surface of the
lumber, permits the claw of the hammer or bar to remove the nail
easily when the form is being stripped from the concrete.
The nails most frequently used with wood and plywood forms
are the common wire type. The sizes and properties of these types of
nails are shown in Table 4-22. Where they are used to fasten form
members together, the allowable loads are based on the resistance to
withdrawal, the resistance to lateral movement, or a combination of
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