• The right concrete mix
• Conditions for transporting the concrete mix
• The correct choice of formwork including uniformity of face contact material
• The release agent
• Consistency of the concrete and its materials
• Quantitative and qualitative selection of the concrete mix materials and composition
• Use of a constant rate of placing
• Uniformity of compaction
• Geometry and dimensions of the element, spacing and sizes of the reinforcement and concrete cover
• Use of a baffle to avoid the direct flow of concrete against the form face
• Walls and columns should have a minimum number of joints and preferably be in one lift
• Features should be designed to be predominantly vertical (such as ribbing), and permit easy runoff of water and dirt, as horizontal or sloping features will often weather badly
• The period between completion of concreting and striking the formwork should be constant for all panels of a wall to minimise variations in colour

Trial Panels (Mock Up)

If a trial run is required, the mock up should be made using similar materials and placing techniques to those planned for the permanent works. Trial panels are used to see how the concrete finishes can be achieved as well as providing a future reference for an agreed finish. 

(Figure 2. Examples of trial panels)

Form Liners

Form liners are non-structural materials used to line the face of the structural forms. They are used to produce either a smoother or more profiled/patterned surface to the concrete. They can also be used to extend the life of old form faces or to enhance the durability of the concrete surface.There are several different types of form liners, which vary based on the application. Single-use form liners are usually made of styrene plastic. Multi-use form liners are usually made of ABS plastic and range in number of uses from 2 to over 10. Multiple reuse form liners are usually made of polyurethane, a heavy rubber material known for its durability.

Other form liner materials used include polystyrene foam, fiberglass and even aluminium–styrene plastic. However ABS plastic and polyurethane are considered to be the industry standard, and are most often specified in plans by architects and engineers.

 

(Figure 3. Examples of form liners use – sound walls)

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Fair Faced Concrete

In modern architecture concrete is not only used as a load-bearing material but increasingly for aesthetic reasons as well. Fair faced concrete is a concrete surface that is left exposed, without any covering applied.

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As the surface of the concrete is visible, it is imperative that the design considers every tie hole position and ply layout, in order to achieve the best finish possible and adhere to the architect’s design.

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(Figure 4. Tie holes and plywood arrangements to fair face concrete)

 

(Figure 5. Fair faced concrete typical finish – From www.doka.com)

 

There are several ‘cheats’ available for achieving these high finish and patterned surfaces, but all need to be considered at the design stage.  For feature soffits it is often economical to use two layers of ply.  The lower layer is ‘used’ and simplifies the falsework arrangement, whereas the upper ‘new’ layer can be placed to give the high-level finish. Again with a wall, high pours require more ties; therefore, panel selection is critical to maintain a pattern.  Alternatively, dummy tie holes can be adopted to give the appearance of a regular panelled approach.

 

Read more of our Technical Guidance.