Having created the main outer concrete cavity for the swimming pool as part of the main basement structure the next stage of the swimming pool construction was to line the cavity with insulation material. The insulation in the form of rigid poly-isocynanuranate foam boards similar to those used to insulate the basement walls was applied to floor and walls of the pool. These boards are about 100mm (4inches) thick and have a very low thermal conductivity to prevent heat loss from the pool water to the surrounding sub-floor of the basement. Pipework for the pool water inlets and water filtration and sterilising system were installed into channels cut into the foam insulation. Similarly conduits that will be used to house the electrical wiring for the lamps that will ultimately installed in the pool were also set into channels cut into the insulation.
Pool insulation with pipework.
When considering swimming pool construction, concrete is the optimum material of choice. The method of creating a single cast shell that is widely regarded as a leading method of construction for high quality, luxury swimming pools is “Gunite”, a dry spray method of spraying concrete. Gunite is a small aggregate and cement, mechanically mixed together and fed, in a dry state, into the hopper of a ‘gun’. The mixture is forced by air, supplied by a 600 cubic feet per minute compressor, to a nozzle, where water is added, and the resulting wet mixture is sprayed at high velocity on to the surface to be ‘gunited’. Other methods of concrete construction include Shotcrete, a ‘wet spray’ method of spraying a high cement content, small aggregate ready mix concrete, at velocity on to the shuttering and reinforcement. These two methods contrast with the poured concrete, or ‘Shutter and Pour’ method which involves pouring concrete into conventional wooden forms as used so far in the construction of the basement. Another option for swimming pool construction is to use masonry block where the walls are constructed with concrete blocks.
Before the gunite is applied however a matrix reinforcing steel mesh was constructed over the base and walls of the pool:
Swimming pool detail showing the thermal insulation, water filtration pipework and steel reinforcing mesh for the gunite concrete.
Applying the gunite concrete. This was really hard work and like holding on to the business end of a rocket!
Close up of the gunite being applied. It was a great demonstration of Newton’s third law of motion: action and equal and opposite reaction!
Another view of how the gunite was built up over the steel reinforcement, layer by layer.
- Gunite applied little by little until the entire pool was covered.
Shaping and smoothing the gunite.
The Gunite or shotcrete method has many benefits:
1. No Joints, No Cracks.
Owing to the way in which the concrete is applied, through a spraying method that typically builds up in layers, the Gunite pool shell is a complete, continuous shape which is important to create a strong pool shell without joints that can give concern for leaks and potential cracking due to movement. Other materials used to construct pools include fibreglass, plastic and metal, but Gunite sprayed concrete creates a strong layered shell, which is extremely hard and dense, making it stronger than normal concrete. From this tough foundation, the pool can then be finished to create a highly durable, luxury swimming pool.
2. New Depths
A pool’s depth can often depend upon the selected method of construction. Some concrete pools are created using hollow blocks, which are filled with a concrete mix to form a solid wall. Pools built in this way however, have limitations on vertical wall depth, in order to withstand the stresses of containing several tons of water and the external soil pressure. Gunite pools can be made to be much deeper because of the high strengths achieved with the method and have no limitations on steel and concrete design.
3. Flexibility of Shape
The Gunite spraying method of construction is ideal for pools with an intricate shape, as the technique provides the flexibility to design and create a pool to any desired shape. Irregular curved shapes are much easier to construct with gunite. Although we haven’t exploited this aspect in the Ridge End pool since we have opted for a simple rectangular shape, the gunite method has made it easier to sculpt the steps and seating area into the pool.
For larger pools, where reinforced concrete would be used, a Gunite sprayed pool would almost certainly be a cheaper alternative. The Gunite method is faster to complete than the conventional shutter and pour method, which helps to speed up the entire construction process.
5. Personnel and Work Space
Gunite requires only a small team of operators, which includes the Nozzle-man, responsible for placing the concrete and controlling its hydration, the Gun-man, who regulates the supply of the mix and the air from the gun and the Mixer Operator who ensures the sand and cement are correctly proportioned and of good quality. The Gunite method is also useful for working on difficult access sites, as the operators require only a 50mm diameter hose to reach the working area, which can be up to 80 metres away from the plant and materials so less space is required during the construction process. This aspect of gunite was particularly advantageous in the confines of the Ridge End basement.
The almost completed pool showing the sculpted steps and seating area at the shallow end of the pool.
The subcontractor that we have engaged to construct the swimming pool is a company called Guncast Swimming Pools. Guncast takes its name from Gunite, having perfected the technique over thirty years of luxury pool design and construction. They will be responsible for the design, construction and installation of the swimming pool structure and all the associated water heating, filtration and sterilisation as well as the air handling of the pool hall ventilation. They will also supply and install the sauna and steam room and associated plant.