The only benefit shotcrete has over gunite is overall cost of the product. Beware of a builder that pushes for the wet-mix shotcrete process, as this is simply a way for a builder to save on their own construction cost, allowing them to pocket some extra money from your project.
A shotcrete company needs to rely heavily on the cement plant that they order their concrete mix from for quality. These cement plants need to make products to hundreds of different specifications and incoming orders each day, leaving you at risk of having your project end up with fluctuating areas of strength. Having to order the material also means that the company needs to wait for the cement plant to deliver. If too much time passes between truck loads of cement, you could end up with a cold joint. This puts the overall structural strength of your project in danger, increasing the chance of splitting or cracking immediately, and decreasing the amount of time into the life of your structure that this will likely occur.
Shotcrete material, since it is pre-mixed, is actually curing on the way to the job site. When it is finally applied to the project, craftsmen need to rush to shape and finish off the material to the desired finish in the limited time they have until it cures fully and becomes hard and unworkable. Adding to the difficulties of shaping the shotcrete, the -0.5-inch aggregate that is embedded into the shotcrete, that is necessary to the structural strength of the product, impedes the craftsmens’ progress, slowing them down where speed is absolutely essential. It is not an uncommon sight to see the contractor you selected that used shotcrete return to your project a few days later with cement chisels, saws, drills, and other tools to fix the shaping errors or even repair the flaws in the shotcrete material.
With gunite, the material is stockpiled at our own yard. A professionally trained rig-operator loads their own mixer personally. They then transport the unmixed material to the job site, where the operator waits for their turn to offload the mixer. There is no rush with gunite because the curing process does not begin until the very moment it is applied to the surface of the project. While, on average, a shotcrete mixer offloads in 15 to 45 minutes, gunite takes more time approximately 45 to 90 minutes per mixer. This extra time ensures that each load of gunite is carefully mixed on site and that the mix is able to be constantly inspected for quality by the rig-operator while their mixer is being emptied.
While shotcrete pours out of the hose already curing, gunite is shot pneumatically at extremely high pressure through the hose while still dry to the nozzle. At the end of the hose, the nozzle-operator hydrates the mixture immediately before application starting the curing process seconds before impact of the material to the surface. The significantly longer curing period and lack of any large aggregate in the material means the craftsmen can take their time, leaving a perfectly finished project to whatever finish or shape the customer desires. The lack of aggregate and the pressure at which gunite is applied allows it to adhere to nearly any surface, therefore filling any void making it the most versatile product on the market for all cement applications.