Gunite is a term for the dry process of shotcrete. Gunite once in place is the same thing as concrete , the main difference is the application process. Gunite is pneumatically applied concrete, which means that a very high volume of air under pressure is used to convey the material down a hose and then shoot it into place at a high velocity. The high velocity is what gives gunite its strength. If material does not come out of the nozzle and stay where its shot then it needs to be removed from the pool. What needs to be removed from the pool is called rebound, which i will cover in my next article. There should be a good amount of what looks like hard grey sand around the perimeter of a pool when the gunite has been applied correctly.
The way gunite works, is first a mixture of 4 parts washed concrete sand and 1 part cement powder is mixed together dry with no water added. The dry mixture then falls down a shoot into what is known as the gun. (two guns side by side are shown in figure 1) Inside the gun is a hopper and at the bottom of the hopper is whats called the bowl which you can see in figure 2. When the material falls into the gun it fills of the holes you see in the bowl. The bowl rotates and when it gets to the point that you can not see is where the air is introduced. High pressure air is blown into the smaller hole forcing the material out the larger hole and down the 2" hose to the nozzlemen (figure 3). The water is added at the end of the hose at the nozzle by the nozzlemen. The nozzlemen is highly trained, experianced, and certified to know how much water to add to make the correct concrete mixture.
Figure 1
Figure 2
Figure 4
