Today, the pool shell of a commercial swimming pool can be constructed in several ways. Two of the most commonly used methods are cast in place concrete and shotcrete. The major difference between the two is quite simply the method of placement. At the end of the day, both systems, with proper design and construction, will provide a rock-solid pool shell which can last for more than 40 years.

CAST-IN-PLACE CONCRETE

Cast in place concrete construction can be a costly and very labour-intensive process. This type of construction requires additional excavation to allow workers room to install an extensive forming system for both the inside and outside of the pool walls, which is used to contain the concrete and shape the pool structure. This working room behind the forming system requires backfilling when the concrete work is complete.

Once the formwork is in place, concrete is discharged from a ready-mix truck, and transferred to the work area by way of boom pump, line pump, buggy, or down the chute directly off the back of the truck. Next, concrete is placed on the ground or in the form work, and then must be vibrated for consolidation & compaction.

Cast in place concrete forming system.		Pouring cast in place concrete.

Advantages:

• It’s the most common type of concrete construction.
• Cast-in-place concrete will result in a strong and waterproof structure with compressive strengths of 4,000 to 5,000 psi.
• When properly designed and constructed, cast in place concrete results in a relatively smooth surface that will require very little surface preparation for the use of epoxy-based pool paint, tile and plaster finishes.
• Cast-in-place concrete results in the most uniform surfaces possible.

Disadvantages:

• Over excavation is required to allow working area behind the forming system.
• Very labour intensive to form the walls.
• Backfilling of the formed walls is required.
• It’s harder and much more complicated to form shapes.
• Generally, more expensive to construct in comparison to a shotcrete pool.

SHOTCRETE

The quality of a shotcrete pool can be comparable to a cast in place pool with one exception. Typically, they do not require extensive forming which often results in cost and time savings. Although the hardened properties of shotcrete are similar to conventional cast-in-place concrete, the nature of the placement process provides additional benefits, such as very fast erection, particularly on complex forms and shapes, including curved walls. Due to the speed of construction and the minimal equipment requirements, shotcrete is a very cost-effective building method.

The shotcrete method utilizes concrete that is discharged from a ready-mix truck into a shotcrete pump and then pneumatically “shot” in place against a wood or earth form. To increase the velocity of the material which improves the control of the “shooting” process, accelerators and other admixtures can be added to the nozzle along with air under pressure. Because shotcrete is "shot" up against wood forms or earth, there is generally very little backfilling required.

Pool form ready for shotcrete.		Shotcrete being "shot" into place.

Advantages:

• No over excavation required. As a result, there is very little to no backfilling required.
• The ability to build in very tight spaces and “free form” applications make it very simple to build pools of any shape.
• Higher compressive strengths than cast-in-place concrete. Typical compressive strengths of shotcrete are in the 6,000 to 7,500 psi range
• Lower construction costs.

Disadvantages:

• There are fewer trained and skilled in the use of shotcrete than that of cast-in-place concrete.
• The finished surface of shotcrete is rougher than a finished surface of a cast-in-place concrete pool. Additional surface preparation is required before the application of epoxy paint. As a result, most shotcrete pools have a plaster finish.