Guniting (Dry-Mix Shotcrete)

Guniting is the dry-mix process of sprayed concrete: a dry cement-sand mixture is conveyed under compressed air through a hose to a nozzle, where water is added at the nozzle and the mix is shot at high velocity onto the receiving surface, where it compacts under its own impact. (In the related wet-mix shotcrete the concrete is fully batched then pumped and sprayed.) IS 456 + specialist guidance govern its use.

It is the standard technique for thin, dense, strongly bonded layers on irregular or overhead surfaces without formwork — repair and strengthening of distressed RCC, jacketing of columns, lining of tunnels/canals/swimming pools, slope and rock-face stabilisation (often with mesh or steel fibres), and refractory linings. Key controls are nozzle distance/angle, rebound loss (15-30% for dry-mix), water control by the nozzleman, and adequate curing; rebound and shadowing behind bars are typical defects.