Views:31 Author:Site Editor Publish Time: 2018-09-17 Origin:Site
For gunite (dry-mix), the builders load the pre-mixed dry material into the hopper of the delivery equipment.
They use compressed air to send the material to the nozzle, where it mixes with water.
Then it sprays out at super high velocity, which compacts the material on placement.
For shotcrete (wet mix), the builders put the fully mixed wet concrete in equipment hopper and compressed air shoots the material to/through the nozzle.
Again, the material sprays out fast and compresses where applied.
Normally if you’re pouring concrete (like a sidewalk) and you stop and later start back up, those two pours won’t bind together. They’ll be two separate pours.
So if you were to stop a rough edge and try to blend the new into the old, it’ll create a cold joint which will look different and most likely crack there.
When you’re guniting, you can stop and start again without creating that “cold joint” or plane of weakness. Because of the velocity the material is applied, it’ll still bond together.
The builders have more work time since they mix the cement on-site and can stop and start as needed.
This process tends to be less expensive than shotcrete.
The gunite process requires a super skilled operator because that person is in charge of the sand/cement/water ratio. An error there can ruin the quality of the concrete.
The dry mixture could clog the hose pipe.
Gunite produces a lot of over-spray, called rebound. It makes a huge mess. You also can’t reuse it, so it’s just wasted.
While builders using shotcrete need to be skilled, they don’t have to be as technically trained as someone working with gunite because the concrete is premixed.
Shotcrete forms a strong and consistent coating.
Shotcrete requires less time.
Since shotcrete is premixed, you have to apply it quickly. You can’t stop and start because it won’t bond.
Cracks can form from shrinkage if too much water is added to the mix.
Shotcrete is more expensive than gunite.
The builders might add water to the cement mixture in the cement truck to keep it from hardening. This can compromise the strength of the concrete.