Types of Formwork (Shuttering) for Concrete Construction

Formwork or Shuttering is a type of mold used for the concrete construction work such as; slab, beam, and columns.

In Sinhalese we called as හැඩයම් ලෑලි, හැඩයම, පැති ලෑලි etc. Mostly used term in construction sector is formwork.

Formwork types in concrete construction is depending based on their raw materials and structural components. Formworks can also be named based on their type of structural member construction such as slab formwork, beam formwork, column formwork etc.

In construction of formwork takes time and involves expenditure up to 20 to 25% of the cost of the structure or even more. Design of these temporary structures are made to economic expenditure. The operation of removing the formwork is known as stripping. Stripped formwork can be reused. Reusable forms are known as panel forms and non-usable are called stationary forms.

Timber is the mostly used/ common material used for formwork. The disadvantage with timber formwork is that it will warp, swell and shrink. Application of water impermeable cost to the surface of wood mitigates these defects.

A good formwork should satisfy the following requirements,

It should be strong enough to withstand all types of dead and live loads.
It should be rigidly constructed and efficiently propped and braced both horizontally and vertically, so as to retain its shape.
The joints in the formwork should be tight against leakage of cement grout.
Construction of formwork should permit removal of various parts in desired sequences without damage to the concrete.
The material of the formwork should be cheap, easily available and should be suitable for reuse.
The formwork should be set accurately to the desired line and levels should have plane surface.
It should be as light as possible.
The material of the formwork should not warp or get distorted when exposed to the elements.
It should rest on firm base.

Economy in Formwork

The following points are to be kept in view to effect economy in the cost of formwork,

The plan of the building should imply minimum number of variations in the size of rooms, floor area etc. so as to permit reuse of the formwork repeatedly.

Design should be perfect to use slender sections only in a most economical way.
Minimum sawing and cutting of wooden pieces should be made to enable reuse of the material a number of times. The quantity of surface finish depends on the quality of the formwork.

Formwork can be made out of timber, plywood, steel, precast concrete or fiberglass used separately or in combination. Steel forms are used in situation where large numbers of re-use of the same forms are necessary. For small works, timber formwork proves useful. Fibre glass made of precast concrete and aluminium are used in cast-in-situ construction such as slabs or members involving curved surfaces.

Types of Formwork (Shuttering) for Concrete Construction

Timber Formwork

Timber for formwork should satisfy the following requirement,

It should be,

well seasoned
light in weight
easily workable with nails without splitting
free from loose knots

Timber used for shuttering for exposed concrete work should have smooth and even surface on all faces which come in contact with concrete.

ඉදිකිරීම් කටයුතු සදහාම ස්වාභාවික දැව කදන් වලින් ඉරාගෙන පදම් කරන ලද ලී පටි ආදිය. මේවායෙහි හරස්කඩ ප්‍රමායයන් 2” x2” / 2” x 4” / 2” x 9” etc. පරිදි වේ.

Advantages of timber Formwork

Economically more advantageous.
Easy to handle and adjust to the desired shape
It can be made in any shape and size.
Damaged parts can be replaced and reused. (Can be used several times.)

Disdvantages of timber Formwork

It is not strong enough to bear large loads/ weight.
Concrete materials such as concrete can leak.

Normal sizes of members for timber formwork

Plywood Formwork

Resin bonded plywood sheets are attached to timber frames to make up panels of required sizes. The cost of plywood formwork compares favourably with that of timber shuttering and it may even prove cheaper in certain cases in view of the following considerations:

It is possible to have smooth finish in which case on cost in surface finishing is there.
By use of large size panels it is possible to effect saving in the labour cost of fixing and dismantling.
Number of reuses are more as compared with timber shuttering. For estimation purpose, number of reuses can be taken as 20 to 25.

Advantages of Plywood Formwork

Large size boards are economically advantageous. Common dimension of plywood panel in - 1220mm(L) * 2440mm(H) * 2.5mm to 18mm(T) available in Srilanka marketplace.
Various thicknesses are available in the market. (11mm, 12mm, 15mm, 17mm, 18mm)
A softer finish is added to the surface of the concrete structure.
Cost, labor and time can be reduce, due to larger boards.

Disadvantages of Plywood Formwork

Low durability, water and collision can separate the boards.
It is expensive compared to Timber.

Steel Formwork

This consist of panels fabricated out of thin steel plates stiffened along the edges by small steel angles. The panel units can be held together through the use of suitable clamps or bolts and nuts. The panels can be fabricated in large number in any desired modular shape or size. Steel forms are largely used in large projects or in situation where large number reuses of the shuttering is possible. This type of shuttering is considered most suitable for circular or curved structures.

Steel forms compared with timber formwork

Steel forms are stronger, durable and have longer life than timber formwork and their reuses are more in number.
Steel forms can be installed and dismantled with greater ease and speed.
The quality of exposed concrete surface by using steel forms is good and such surfaces need no further treatment.
Steel formwork does not absorb moisture from concrete.
Steel formwork does not shrink or warp.

Advantages of Steel Formwork

Ability to withstand large loads.
Easy; Can be used for construction, partitioning, handling and repetition.
There is no contraction due to temperature.
It is very profitable due to its high reusability.

Disadvantages of Steel Formwork

The structure is limited to the shape, meaning that the length of the structure with the corresponding workpiece is not made of steel.
Standard steel unit is very heavy and difficult to handle.

Construction of Concrete formwork

This normally involves the following operations,

Propping and centring
Shuttering
Provision of camber
Cleaning and surface treatment

Order and Method of Removing Formwork

The sequence of orders and method of removal of formwork are as follows,

Shuttering forming the vertical faces of walls, beams and column sides should be removed first as they bear no load but only retain the concrete.

Shuttering forming soffit of slabs should be removed next.

Shuttering forming soffit of beams, girders or other heavily loaded shuttering should be removed in the end.

Rapid hardening cement, warm weather and light loading conditions allow early removal of formwork. The formwork should under no circumstances be allowed to be removed until all the concrete reaches strength of atleast twice the stresses to which the concrete may be subjected at the time of removal of formwork. All formworks should be eased gradually and carefully in order to prevent the load being suddenly transferred to concrete.

Below figure's shows formwork for different types of members in civil engineering construction.