Unless you work in the industry, concrete is a mystery. Many types of formulas exist, with highly technical jargon such as “entrained air” or “slump” thrown in the mix. Add to this is the application methods and materials used in the mix. Somehow, you have to make sense of it all to understand the differences between Gunite and Shotcrete.
First and foremost, concrete is a mixture of Portland cement (roasted limestone and other minerals), sand, and small rocks. The sand and small rocks are called “aggregate.” The end result is when all the dry stuff is mixed with water, it becomes concrete. Concrete is putty-like when wet, but hardens to become rock when dry, hence, in effect, its “pourable rock.”
Now you understand a little about concrete. Onward to Gunite and Shotcrete. First and foremost, all the dry mix (aggregate plus cement) in Gunite and Shotcrete is exactly the same. Both Gunite and Shotcrete is shot out of a high pressure nozzle, so it can cling to vertical walls. It’s when the water is added to the dry mix that makes the difference.
Gunite: Water is added to the dry mix right at the nozzle. The dry mix is trucked in to the jobsite, and shot out of the nozzle. A water injector is installed at the nozzle opening. Water is added to the dry mix right at the nozzle opening and a second before it hits its target. In effect, the concrete is made in the air, right before it hits the target. This has useful applications. Concrete has a very specific curing time. If the job site is far away from the plant, a “wet mix” will harden up right inside the mixing truck while in transit.
Shotcrete: Shotcrete is trucked in wet, with the water and dry mix already combined. It is shot out of the nozzle premixed and “wet.” This has its advantages as well. Some industry experts state that combining the dry mix with water is an exact science. If the installer is using Gunite and doesn’t get the water ratio “just right,” the end result is the concrete will be weak.
Overall, no one method is far better than the other. It all boils down to craftsmanship. If the installers are true craftsmen, the job will last for years.
If you need help with your shotcrete project, give us a call. We’d be glad to assist you.