If you are installing an in-ground swimming pool or spa, the contractor will in all likelihood use a substance known as shotcrete. This substance is also used to repair buildings and in applications in which special shapes and forms are desired that cannot be achieved with conventional molds. Shotcrete was first used in taxidermy in the early 1900s and has evolved to become a major building component in the 21st century.
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What Is Shotcrete?
Shotcrete is either mortar or simple concrete. In most uses today, the mixture is concrete. The difference between shotcrete and regular concrete is that shotcrete is shot out of a high-pressure nozzle. (shot + concrete = shotcrete) The shotcrete is propelled at a high enough rate of speed that it is compacted and placed as it is applied. The application can be either a wet or dry mixture.
The best known application for shotcrete is in the construction of in-ground swimming pools. The shotcrete can be projected at the walls and slopes of the pool surface without the need of forms or molds. A skilled applicator can apply the shotcrete evenly and smoothly in a very short period of time. Shotcrete is also used in building repair, due to its unique application and properties. The shotcrete can be aimed and applied to surfaces at any angle, including overhead. Since shotcrete is applied through a hose and nozzle, it is possible for workers to move in tight spaces. The only limitation is the strength of the pump and how much hose can be used in the application process.
In very small applications no reinforcement is required. In larger projects, steel rods (rebar) are used to reinforce the structure or form. Other applications use fiber or a steel mesh. In many cases the shotcrete is applied to what is little more than the type of metal fence used to line pastures. The actual type of reinforcement required depends on the size, shape and strength requirements for the project.
Wet vs. Dry
The contractor will decide which method of application is best for your project. Each process has its advantages. The dry mix is preferred when working on a series of small jobs, as it is easier to clear from the nozzle. The other major advantage of the dry mix is that the water is mixed at the nozzle and can be adjusted by the operator. This makes the mixture easier to apply in overhead applications. The wet mix produces much less dust and can be applied at a much faster rate than the dry mix. The wet mix also has less waste, so it is more economical.
Is Gunite the Same Thing as Shotcrete?
Yes and No. Gunite is the name given to the dry mix process only, but is different from the wet mix process. Since the process is almost identical in both, and the end result the same, many people have mistakenly assumed gunite was the proper term for the process, both wet and dry. The dry mix can correctly be called either Shotcrete or Gunite. The wet mix should only be referred to as shotcrete.