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Swimming Pool construction can appear a confusing and complex subject. At Ascot Pools we believe that by explaining the principles of swimming pool construction in clear and simple terms a prospective pool owner will appreciate the work, effort and experience that must go into a pool installation to ensure that it is safe, attractive and well built.
Essentially there are 4 broad types of swimming pool shell construction.
This system of pool construction employs a reinforced concrete floor slab with steel starter bars left in the vertical at the thickened edge (300mm) of the floor as above. A proprietary block system with interlocking edges is then constructed to form the pool walls. The wall can be constructed with either a 130mm or 230mm cavity
The major difference between this and the hollow block system above is that the blocks in a permanent shuttering system are open at the end, allowing vibrated concrete to flow around the wall cavity thus forming a monolithic shell as the vibrated concrete is reinforced without any divisions between the blocks. As the name suggests the shuttering remains in position after the concrete is poured.
This method of swimming pool construction can be designed so that the strength of the pool can be proven by calculations prepared by a structural engineer.
Such a method is ideally suited to indoor swimming pool construction as the pool wall can be built sufficiently strong so that it can support the wall of the pool building's superstructure. A wall constructed with 230mm cavity blocks can be self - supporting and is not reliant on the support of backfill material for added stability. This feature is especially useful if part of the pool wall is projecting above existing ground level.
A cage comprising 2 layers of steel reinforcement is set within the pool excavation to form the shape of the pool walls and floor. Pool fittings such as skimmers, inlets and drains are then fitted into the steel cage in the appropriate position. The steel cage is then sprayed with pre mixed concrete to a thickness of not less than 220mm in the wall and 300mm - 350mm in the floor. The most effective form of sprayed concrete for swimming pool construction is 'shotcrete', where premixed concrete is poured into a 'shotcrete' trailer pump before being sprayed pneumatically at high pressure through a delivery hose onto the steel cage.
The major advantage of this system is speed; typically a 10m x 4m outdoor swimming pool construction can usually be formed in a day, once the steel cage and back shuttering has been set up. The 'shotcrete' system has the added advantage that almost any shape of pool can be constructed so it is especially suited to projects requiring special shapes or 'free form' pools.
If access to the site is limited then this system is ideal, especially for indoor pool construction as it enables the building of concrete pools in confined areas with poor access such as basements and other sites where working space is at a premium.
Sprayed concrete shells can also be structurally calculated as the structure is monolithic and therefore has no joints.
Finishes for all the above construction types usually include a waterproof render of 20mm - 25mm and are then tiled using glass or ceramic tiles and finally finished with a waterproof grout.
Filtration and pipework is common to all the types of swimming pools construction whatever their method. Flow and return pool fittings, together with underwater pool lights are fitted in the pool shell before the pouring of the concrete. Puddle flanges are used behind the fittings to prevent leaks.
Such pools are monolithic in design and are usually manufactured in a factory off – site to a standard size and depth.
This type of pool is generally manufactured using glass reinforced plastic, acrylic and or composites and formed as a one piece pool shell in a mould. The pools can be plumbed in the factory and the pipework pressure tested before delivery to site.
After the hole for the pool has been excavated, a lean mix of sand and cement is used to provide a firm and level base to support the pool shell. Generally the pool is backfilled with pea shingle whilst the pool is filling to prevent settlement of the surround. The major benefit of this type of pool is that a consistent quality of finish can be maintained in a factory environment, producing a monolithic structure and reducing the risk of leaks. The installation time is faster, enabling completion of the pool in a much shorter time than conventional swimming pool construction.
The advances in plastics technology in the early 1950s enabled the development of the liner pool and this was a major departure from the traditional pool construction techniques used hitherto
Liners are manufactured off site in a factory to specific dimensions and available in different colours and patterns which are usually solvent printed onto a plain material.
The strength and flexibility of modern pool liners eliminated the need for a reinforced concrete floor. After the pool excavation is hand trimmed, a mix of sand /cement is applied as a screed directly onto the earth to form the pool floor of between 50mm – 75mm thick. If the ground conditions are poor then a lean mix of concrete is laid to provide a sub base for the pool floor.
The pool floor is formed at an angle to the pool walls, eliminating the cost of an expensive deep vertical wall by using reveals or batters to form the interface between the floor and the wall. By maintaining the angle of repose of the pool floor at 45 degrees to the pool wall, a constant wall height of around 1 metre can be used. This substantially reduces the volume and area of the pool floor. The wall construction used in this type of swimming pool construction is not reinforced and may be constructed using preformed galvanised panels or dense concrete blocks of 7.3N/mm2 strength measuring 440mm x 215mm x 215 mm laid face down. Alternatively proprietary panels manufactured in GRP or polymer, which are bolted together and braced at intervals with concrete strengthening at the panel joints.
The profile of the pool floor is accurately shaped to specific dimensions to ensure that the manufactured PVC liner fits precisely and conforms to the designed profile of the pool shape and depth.
Lower costs and consistent quality resulted from manufacturing tough, flexible and waterproof swimming pool liners using factory production techniques.
This method of pool construction results in large savings in the construction of the pool as it does not require a steel reinforced concrete floor, or labour intensive finishes such as tiles.
Swimming pool construction using this technique is very much faster than traditional methods as there is a shorter drying time for the wet materials that are used. Liners enable faster construction than traditionally constructed pools as the pool can be filled immediately after the liner is fitted and the pool can be completed
Pool fittings for this type of pool construction use a special rubber gasket and plastic faceplate to provide a water proof seal between the liner and the pool wall.
Repairs to swimming pool liners can be made by using a water activated adhesive and patches which enable repairs to be made quickly and usually without draining the pool.
For professional advice on your pool project telephone us today.
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