Sprayed versus Boxed and Pour Swimming Pool Construction

Construction Methodology

Sprayed (shotcrete) v Boxed & Pour Swimming Pool Construction Construction Methodology The construction methodology is to construct half of a 25m long pool in a single concrete spray. The walls and wet deck are constructed first starting at the base of the wall and working around in order to build up the wall. The concrete is first sprayed on the back side of the wall in a small section before the front face is sprayed whilst the back concrete is still wet (typically a minute later). The nozzle is angled in order to mitigate the chance of shadowing by compacting the rear concrete behind the reinforcement. Once the walls are poured the floor is poured/sprayed and vibrated. With regards to sequencing and time durations, a concrete sprayed (shotcrete) pool will be quicker to construct than a box and pour pool. The pool (up to a construction joint) is poured in a single day. Any dividing walls typically have starter bars in place for box and pour at a later date.

Procedure for constructing wet deck trenches and all construction joints

The wall and back side of the wet deck are sprayed first and then the prefabricated formwork boxes to form the wet deck are put in place. The front of the wet deck is then sprayed. This ensures that no honeycombing occurs.

Confirmation of dimensional accuracy

The dimension accuracy is as good as a box and pour or better. This is because the dimension accuracy is checked during construction so there is no chance of formwork slip occurring to the front face of the pool.

A guarantee for strength, durability, and water tightness in accordance with the standard

Sprayed concrete (shotcrete) construction provides a water tight or more water tight than box and pour construction as there are no cold joints. Our pools will meet the requirements of AS3735 Concrete structurers retaining liquids.

Confirmation of concrete mix design in accordance with the standard / project specification and that the same can be successfully sprayed

Confirmation of concrete mix design in accordance with the standard / project specification and that the same can be successfully sprayed Our pools will meet the requirements of AS3735 Concrete structurers retaining liquids. The specified concrete mix achieves a minimum of 40MPa and has a low water cement ratio to control shrinkage.

Confirmation of concrete supply reliability during construction (to ensure that enough concrete can be continuously supplied on the day)

It is our experience that the concrete pour is organised well in advance and as such the availability of the spray is as guaranteed as any box and pour construction. The experience of the contractors involved provide them with an understanding of when each concrete truck will be required and continual communication with the concrete supplier guarantee that there are no issues with supply.

Risk assessment to address how to minimise construction risk as compared to the build certainty of box-and-pour construction

Risk assessment to address how to minimise construction risk as compared to the build certainty of box-and-pour construction Provided contractors in the vicinity of the concrete spray (shotcrete) are wearing safety glasses and other trades are not allowed close to the pool on the day of the concrete spray (typically just a couple of meters) there are no additional risks to workers. FMG Engineering, South Pacific Commercial Aquatics’ aquatic consultant offer the following additional comments in relation to the comparison of sprayed concrete (shotcrete) and box and pour concrete regarding the pros and cons of each. The largest issue with constructing a box and pour pool is the cold joint which is formed at the interface of the walls and floors.

This location becomes a weak point in the construction which cannot be eliminated through box and pour. There is also a risk during box and pour construction of honeycombing at the base of the wall. in theory, this should not occur as many concrete contractors are familiar with pouring concrete however FMG encounter this regularly in swimming pool construction even with experienced contractors.

Both of the above issues are eliminated with sprayed concrete (shotcrete). There is no cold joint at the interface of the wall and floor which is inherent in a sprayed concrete pool. The risk of honeycombing is mitigated as the front face of the wall is visible. However, there is a risk of shadowing occurring. Shadowing is an air pocket behind the reinforcement in the concrete, If this occurs then the structural capacity and water tightness is compromised. By using experienced and competent contractors, the risk of shadowing is heavily reduced. FMG are of the opinion that a sprayed - concrete pool (shotcrete), by an experienced and competent contractor, has equivalent structural properties, improved water tight properties through a reduction in cold joints and a general improved long term quality. FMG Engineering, South Pacific Commercial Aquatics’ aquatic consultant, is happy to discuss the comparison of box and pour vs sprayed concrete pools should you wish.

Contact, Ashley Holmes, Senior Aquatic Engineer, ph: 1300 975 878, email: This email address is being protected from spambots. You need JavaScript enabled to view it..