Instament vs. Shotcrete vs. Gunite
Instament spray concrete is not to be confused with Shotcrete or Gunite.
Instament Spray Concrete- Spraying
"Spraying" means the wet (mixed on location in the hopper with a chemical mix) concrete is pumped through a tiny nozzle. The spray is fine and the operator dusts the rebar and rib lath which is pneumatically applied. It dries very quickly so the operator can dust the next coat without waiting for drying time. It has an expansion ratio of 20% and contains millions of tiny air cells that provide outstanding thermal insulation. Operator instruction is important only for application purposes, as there is no danger in application due to low velocity projection of concrete . Mistakes in application are usually far less critical than with Shotcrete and Gunite. Rebound or the waste created by sprayed concrete falling to the floor, is minimal compared to Shotcrete and Gunite. The finished product is a 4" wall at 3000 psi. The density is less compared to the density of Gunite and Shotcrete. The concrete contains a proprietary admixture that allows it to placed without the need for formwork. Instament was developed by Donald Sirianni and a chemist in 1964.
Gunite- Dry Gunning
"Gunite" is a trade name for "dry gunned" concrete, invented and patented by a man from North Carolina. The term "gunite" has been used so much that, to most people, it means spray applied concrete. People often talk about a gunite pool, meaning a concrete pool where the concrete is pneumatically applied or sprayed in place using air pressure. Aggregate is part of the concrete mix. Gunite requires form work and certified operators as the application can be dangerous as the concrete is projected at high vilocity. "Dry gun" means the cement and sand are injected into an air stream conveying it to the nozzle. The nozzle operator then adds the water at the nozzle and has total control of the water-cement ratio. The delivery hose of the mix is generally quite light, the nozzle is about 11/2 -2 inches in diameter and the hose is mostly filled with air containing the mix of cement and sand. Dry gunning allows concrete to be placed drier than most "wet gunning." Often the concrete is stacked at a very heavy thickness and this can be a disaster for an Airformed structure. Operator training is very critical and can mean the difference between success and failure of application.
Shotcrete- Wet Gunning
"Wet gun" means the wet (already mixed) concrete is pumped to the nozzle. Air is added at the nozzle to carry the concrete mix to the target and again pneumatically applied. We call the system "wet gunning." Here too operator training is important, but not quite as technical for wet gunners. Mistakes in application are usually far less critical than with dry gunning in building construction. Rebound or the waste created by sprayed concrete falling to the floor, is usually half as much for shotcrete as compared to gunite. Aggregate is part of the mix. Shotcrete requires form work and certified operators as the application can be dangerous due to the high velocity projection and for success of application.