Manufacturing Process

There are two methods of producing GRC components as classified in BS EN 1169 and BS EN 15191.

Premix Process
As the name suggests cast pre-mix is a process where the fibres are added to the concrete slurry during the mixing process. The mix is then poured or pumped into a mould using very similar methods to precast concrete. Moulds are generally two-part to create hollow core items or encapsulate a lightweight core such as polystyrene. Because the mix is required to be relatively viscous, fibre content is at the lower end of the scale. The lower strength of the material generally means it is generally only suitable for smaller architectural details such as band courses, copings etc.

Slightly higher strengths can be achieved using pre-mix which is sprayed into open moulds. This process can offer cost savings as moulds are much simpler to manufacture.

Spray Process
Sprayed GRC is recognised throughout the world as being the ultimate production method in terms of performance and flexibility. Considerably higher ultimate bending strengths are obtained by the use of a higher fibre content, longer fibres and a lower water/cement ratio. The increased ductility of this material allows designers to utilise panels which can be as large as 10-15m².

Because of the high fibre content the cement slurry and fibres are applied directly to the mould surface using a simultaneous spray technique. This is a highly skilled operation which unlike Premix GRC has little in common with most other forms of pre-cast concrete. As a result it tends to be only manufactured by specialist GRC producers such as GRCUK.