The sand and cement are mixed dry and then the water/admixture and polymer (if used) are added. Generally a two speed slurry/fibre blender mixer is used. With this type of mixer, the fast speed is designed to create a smooth creamy slurry. This takes about 1 – 2 minutes. The mixer is then switched to slow speed and fibre in the form of chopped strand (length approximately 13mm) is added slowly. The fibre is blended into the mix for approximately 1 minute.
Once the mix is ready, it is poured into moulds which are vibrated using a vibrating table. The product is left in the mould and covered with polythene to prevent moisture loss until6 to 8 hours then demoulded.
After demoulding the products are cured under polythene sheets to maintain moist conditions for approximately 7days. Alternatively a polymer curing compound can be used as described for the sprayed process.
The strength of Sprayed GRC is generally higher than Premix GRC.
The table below shows typical values for Sprayed GRC and Premix GRC manufactured with 5% and 3% (by weight of mix) alkali resistant glass fiber.