The two basic methods for applying shotcrete are the dry-mix process and the wet-mix process. The term gunite is frequently used when referring to the dry-mix method; other terms such as air-placed concrete, gunned concrete and sprayed concrete have also been used in the past to describe the process.


In this process, cement and moist aggregate are mixed and then placed into a device that meters the mixed material into a stream of compressed air. Material is carried by the compressed air through a delivery hose to the nozzle where water is added under pressure through a perforated ring. The water thoroughly wets the other ingredients as the mixture is jetted from the nozzle at high velocity onto the surface to be shotcreted.


In the wet-mix process, all ingredients are first mixed to produce mortar or concrete. The mortar or concrete is then placed into delivery equipment. The material is forced through a delivery hose to the nozzle where compressed air is injected to increase velocity.


Bonding ability of dry-process shotcrete is excellent because of the low water-cement ratio and high impact velocity. One of the more attractive features of the wet-mix systems is that the water-cement ratio can be controlled more precisely.