are that the water content can be adjusted instantaneously by the nozzleman, allowing more effective placement in overhead and vertical applications without using accelerators. The dry mix process is useful in repair applications when it is necessary to stop frequently, as the dry material is easily discharged from the hose. Wet-mix shotcrete involves pumping of a previously prepared concrete, typically ready-mixed concrete, to the nozzle. Compressed air is introduced at the nozzle to impel the mixture onto the receiving surface. The wet-process procedure generally produces less rebound, waste (when material falls to the floor), and dust compared to the dry-mix process. The greatest advantage of the wet-mix process is all the ingredients are mixed with the water and additives required, and also larger volumes can be placed in less time than the dry process concrete. Shotcrete machines Shotcrete machines are available which control the complete process and make it very fast and easy. Manual and mechanical methods are used for the wet spraying process but wet sprayed concrete is traditionally applied by machine. The high spray outputs and large cross-sections require the work to be mechanised. Concrete spraying systems with duplex pumps are mainly used for working with wet mixes. Unlike conventional concrete pumps, these systems have to meet the additional requirement of delivering a concrete flow that is as constant as possible, and therefore continuous, to guarantee homogeneous spray application'. Depending on the fineness of the filler, mortar shotcrete mixtures are distinguished (fraction size up to 2.5 mm); shotcrete (up to 10 mm) and syringe concrete, or sprayed concrete (up to 25 mm). Shotcrete vs. gunite Gunite was originally a trademarked name that specifically referred to the dry-mix pneumatic cement application process. In the dry-mix process, the dry sand and cement mixture is blown through a hose using compressed air, with water being injected at the nozzle to hydrate the mixture, immediately before it is discharged onto the receiving surface. Gunite was the original term coined by Akeley, trademarked in 1909 and patented in North Carolina. The concrete mixture is applied by pneumatic pressure from a gun, hence gun-ite. The term Gunite became the registered trademark of Allentown Equipment, the oldest manufacturer of gunite equipment. Other manufacturers were thus compelled to use other terminology to describe the process such as shotcrete, pneumatic concrete, guncrete, etc. Shotcrete is an all-inclusive term for spraying concrete or mortar with either a dry