The spray process requires a mix that is fluid enough for continuous pumping, spraying without blockages and proper compaction. The spray premix needs a certain viscosity to enable the spraying of near vertical mould surfaces.
Depending on the existence of vibration and its magnitude, the workability of cast premix can range from ‘zero slump’ to ‘self compacting’ level. In general, the water cement ratio should be minimised to reduce the shrinkage of GFRC and increase the strength of the product.
The slurry for the spray process is normally mixed in a ‘high shear’ mixer and for premix, usually a two stage mixing process is adopted in which the slurry is prepared at high speed followed by a slow blending phase in which the fibers are incorporated.
The actual mix formulation depends upon the type of product being made and the material availability, the ‘right’ formulation can only be obtained by trial.
Typical Mix Formulations