Formwork

Formwork gives concrete its SHAPE.
Formwork provides a mould, into which concrete is placed.
When concrete has hardened the formwork is removed.
Formwork must be:
ACCURATE
STRONG, and
WELL MADE.
Formwork that is not will leak from the joints, may sag, bulge or
move and, especially in large construction, will not be safe.
The surface of the forms in contact with concrete affects how
concrete will look. If the final look of the concrete is important choose
a material which will leave the surface texture wanted.
PLACEMENT Be sure that formwork is placed so it can be removed. If formwork is placed
in awkward positions or tight corners it may be difficult to remove when the concrete had
hardened.
It is helpful if formwork is:
SIMPLE to build,
EASY to hand, and
RE-USEABLE.
Formwork sections should be of simple design, not too big and of standard sizes if they
are to be re-used.
MATERIALS Formwork is normally made from steel or timber. Timber is easy to make
into formwork while steel will allow a greater number of re-uses.
Formwork can be made on site or bought from formwork suppliers. Special forms made
from various materials can be purchased for forming waffle slabs, circular columns and
other special profiles.



REMOVAL TIMES Form Oil should be applied to the inside of the formwork to stop it
sticking to the concrete and make removal easier. Coat BEFORE the reinforcement is put
in place. Formwork may be left in place to help curing.
See CHAPTER 10 Curing Concrete
Removal time may vary according to the weather,
In cold weather, concrete may take longer to gain strength than in warmer weather,
therefore removal times will be longer.
In normal conditions (around 20°C) 7 days is long enough to leave the forms in place
unless the concrete is suspended when other conditions apply.