What is a gunite? Gunite, often confused with shotcrete but technically different， "gunite" is a construction material made of a dry mixture of cement and sand, sometimes with additives, that is pneumatically projected at high velocity through a hose. It’s mixed with water as it exits the nozzle, creating a dense and durable layer of concrete. Gunite is commonly used in constructing swimming pools, tunnels, retaining walls, and structural repairs due to its flexibility and strong adhesion to various surfaces.

　　The term "gunite" was first patented in 1926 by Charles Adler, who developed the technique using a pneumatic spraying device called a “concrete gun.”

　　How do you spray gunite?

　　Spraying gunite involves several steps to ensure a strong, uniform finish:

　　1. Preparation: Before spraying begins, the surface must be clean and structurally sound. This may involve removing loose debris, applying a bonding agent if necessary, and preparing any formwork.

　　2. Dry Mix Preparation: The dry ingredients are measured and fed into the gunite machine’s hopper. Air from a compressor pushes this dry mix through the hose.

　　3. Hydration at Nozzle End: Just outside the nozzle, water is introduced to the dry mix, hydrating it immediately. The exact amount of water added can vary based on the project requirements.

　　4. Application: The operator aims the nozzle, maintaining a consistent distance and angle to the surface to ensure an even coverage. This process requires skill and experience to manage the speed and direction effectively.

　　5. Finishing: Once the gunite has been applied, it's troweled to create a smooth surface, helping to remove air pockets and enhance the final appearance and strength.

　　Key Components of Gunite

　　The main components of gunite include:

　　- Cement

　　- Fine sand

　　- Aggregates (small rocks)

　　- Water

　　- Sometimes, admixtures such as accelerators or retarders

　　These ingredients are combined in specific ratios to achieve the desired strength and consistency suitable for various applications.

　　Gunite unlike wet-mix shotcrete, which is mixed with water before being pumped through hoses, gunite mixes water only as it leaves the nozzle, making it easier to transport over long distances without setting prematurely.