When it comes to building swimming pools, terms like Gunite, Concrete and Shotcrete are often used interchangeably and erroneously. The fact is they are all basically the same product, concrete, with variations in strength, inherent water-tightness, and methods of construction. This article clears these misconceptions and clarifies why shotcrete is considered the best method for swimming pool construction.
What is Shotcrete and Gunite?
According to American Shotcrete Association, shotcrete is an all-inclusive term to describe the spraying of concrete or mortar through either a dry- or wet-mix process. Gunite refers only to the dry-mix process in which the dry cementitious mixture is blown through a hose to the nozzle.
“Wet shotcrete” (commonly referred to as shotcrete) is factory-mixed wet concrete delivered to an on-site concrete pump by a concrete truck.
“Dry shotcrete” (commonly referred to as gunite) is mixed dry on-site by workers, pumped dry through a hose, and then hydrated when a nozzle-man adds water to the mix as it exits the hose. This requires a very highly skilled nozzle man, especially in the case of thick or heavily reinforced sections.
The use of the term “shotcrete” first occurred in Railroad Age magazine more than 50 years ago in place of the then proprietary word “Gunite,” and has been used by the American Concrete Institute since at least 1967 to describe all sprayed concrete or mortar.
Shotcrete Construction Process
A quality construction ensures the maximum design life from your pool. As shotcrete is a free form of concrete, it can be applied horizontally or vertically and can even be shot upward to adhere and form to the underside of a ceiling. This creates very strong and watertight structures following any type of geometry. Shotcrete is applied pneumatically through the use of a pump, hose, and a specially designed application nozzle. The formula for concrete in a shotcrete application has a higher amount of cement and a lower amount of water than that of “cast-in-place” concrete. The formula results in a concrete mix that is dry enough to be applied to vertical surfaces such as pool walls.
A shotcrete pool is constructed by first excavating and installing back boards for poor ground conditions, and ensuring construction meets design engineer specifications. Plumbing and electrical features are installed, followed by the high velocity application of shotcrete, using the latest shotcrete pumps. Once the concrete arrives at the jobsite, it is poured into the shotcrete pump and sprayed under pressure into place in layers through a back-and-forth motion of the nozzle. The shotcrete application continues until the designed wall thickness is achieved. Experienced shotcrete personnel apply the shotcrete methodically over, around and through the steel reinforcing mesh, guaranteeing excellent compaction.
Advantages of Shotcrete
Shortcreting offers the builder and designer more flexibility and design creativity, besides the obvious construction benefits as listed below:-
- When properly designed and constructed shotcrete pools are the strongest and most watertight.
- Shotcrete is perfect for extremely rapid construction, especially when compared to the other options of block-filled walls or reinforced concrete options.
- Because of the lower volume of water used in the concrete mixture, there is less volume change from water hydration, which results in much fewer joints in the pool between wall sections, than with a cast-in-place wall.
- Higher compressive strengths, in the range of 6,000 to 7,000 psi, than cast-in-place concrete.
- Free form application creates strong and watertight structures of any shape and design.
- The certainty and reliability of employing wet concrete, mixed to exacting specifications in a factory-controlled environment, which is trucked directly to the pool site ensures quality, strength and integrity of construction materials.
As is critical with any construction, even with using shotcrete for pool construction the contractor building it must be highly experienced. When done properly, shotcrete results in a much stronger and watertight pool installation than with cast-in-place.
Here at Davis Concrete, we go beyond simply offering concrete supplies. Our staff also provides the knowledge and experience to help you choose the right product for your job.