Swimming pool construction
A swimming pool is a water retaining structure used for purposes such as leisure and exercise. Pools can be sunk into the ground or built above it, as a freestanding construction or as part of a building or other structure such as a ship.
There are many different types of pool, including:
 Private pool
These might be constructed in a garden, inside a building or built into a basement. Sizes vary but average between 3.7m x 7.3m to 6.1m x 12.2m.
 Public pool
Most public swimming pools are rectangular, 25-50 m in length. They can vary in size, shape, and depth, and can include artificial waterfalls, fountains, wave machines and bridges.
 Competition pool
These must conform to the standards set by FINA, the International Swimming Federation, which requires that pools are 25 or 50m long, at least 1.35m deep, and at least 8-lanes wide. These pools are generally indoors to conform to heating and lighting requirements, and may have starting blocks, electronic timing, results screens, warm up and warm down areas and so on.
 Infinity pool
Typically found in luxurious resorts or hotel settings, an infinity pool features water flowing over one or more edge, giving the visual impression of merging with the ocean or sky. A ‘weir’ is constructed slightly below the pool level where the pool edge terminates. Below the weir, collects water spilling over the weir before being pumped back into the pool.
Pools must be designed and installed to meet water-tightness criteria set out in British Standard 8007:1987. This states: ‘During the 7 day test period the total permissible drop in water level after allowing for evaporation should not exceed 1/500th of the average water depth of the full tank, 10 mm or another specified amount.’
While pool design and construction methods vary, typically they rely on the similar plumbing and filtering systems.
There are different filtration systems, such as:
 Diatomaceous Earth (DE)
This uses mined fossilized exoskeletons of tiny diatoms to act as tiny sieves to remove debris. They are capable of filtering particles as small as 5 microns, although they are the most expensive option and require more maintenance.
Water is pushed through a bed of filter sand and removed at the bottom through a set of lateral tubes. As the filter sand becomes plugged with debris from the pool, the pressure increases on the filter and the water flow drops, at which point the sand needs to be replaced.
Water passes through a filter material which captures debris.These are economical as they don’t need to be replaced as often as sand.
 Method of construction
The main difference between pool types is the method of construction for the ‘basin’.
 Above-ground pools
These tend to be the cheapest and easiest to construct and are usually assembled from pre-fabricated kits. However, there can be safety concerns, as it can be difficult to see into the pool from the surroundings.
 Fibreglass pools
Fibreglass-reinforced plastic can be moulded into a basin shape to the required specifications. A hole is excavated, the necessary plumbing laid, and the pool is lowered into the hole, with sand filler used to fit the exact shape. The area around the pool is backfilled and usually a concrete deck structure is constructed around the perimeter.
 Vinyl-lined pools
A hole is excavated, and a metal, plastic or timber frame wall assembled around the perimeter. Sand filler laid at the bottom of the hole, and a vinyl-lining secured to the perimeter wall. These tend to be cheaper than other in-ground designs but are less durable, as the liner requires replacement typically every ten years.
 Gunite pools
Once a hole has been excavated and the plumbing is in place, a framework grid of rebar is laid. This is sprayed with a heavy coating a gunite, a mixture of cement and sand. This is trowelled smooth and left to cure. The pool may be finished with plaster, concrete paint, tile, exposed aggregate (placing concrete before removing the outer ‘skin’ of cement paste to reveal decorative coarse aggregate), or fibreglass.
These are similar to gunite pools, but rather than spraying gunite, concrete is poured into conventional timber formwork. An alternative method is for walls to be constructed using concrete blocks. These have become less common as gunite techniques have developed.
Other items that may be included in swimming pool construction include:
- Recessed rest ledges.
- Overflow channels.
- Starting platform upstands.
- Ladders: Types include recessed into pool tank, built-in and tiled, face-fixed stainless steel.
Where tiles are installed in swimming pools onto renders and screeds the levelling mortars should be cured and then allowed to air dry. Tiles should have a low water absorption of 3% or less, and adequate slip resistance for the use location.
It is important that the adhesive and grout used for the bedding and grouting of tiles can resist the effects of the pool water and chemicals, or long-term durability may be compromised. The type of adhesive and grout to be used is dependent on several factors, such as:
- The type of tiling.
- The mains water quality.
- The chemicals used for pool water treatment and maintenance.
- The pool design and location of tiling.
There are two main types of sealant used in pools as a means of sealing leaks:
- Epoxy-based sealants.
- Unplasticised polysulphide sealants.
Demarcation lines, pool guidelines and warning lines can be incorporated in the design of the tile layout with contrasting colours. Common colours include white, black, turquoise and blue. For safety reasons, dark tiles should not be used for the pool base they make it difficult to perceive the depth of the water. Special screen-printed tiles can be used for lane or depth markers.
Stainless steel provides a wide ranging and vital service to industry, the leisure market and other sectors, stemming from its very specific properties. The characteristics most commonly relied upon are its resistance to corrosion and its appearance. However, it also exhibits other benefits such as low susceptibility to bacteriological retention and improved fire resistance and ductility compared to carbon steels.
Notwithstanding these attributes, care is required when selecting the specific grade of stainless steel as, in swimming pool environments, stress corrosion can result. This is clearly of vital importance if the use is for structural purposes or if failure might cause harm or damage. This latter category might encompass items not ordinarily thought of as ‘structural’, e.g. advertising sign support brackets.
Swimming pool building environments can create very aggressive situations stemming from high temperatures, the number of users and the chemical disinfectants used. Stress corrosion cracking may occur under a specific combination of the three following conditions:
- High applied stress levels in the component (arising from applied load or from residual stresses from welding or forming the component).
- Susceptible grades of steel.
- Specific aggressive environment.
Stress corrosion cracking relates only to components in the pool atmosphere and not those fully immersed in the pool water.
 Related articles on Designing Buildings Wiki
- Basement excavation.
- Best gym architecture in the world.
- Building foundations.
- CIBSE Case Study London Olympic Aquatics Centre.
- Planning permission.
- Reservoir construction.
- Scunthorpe Sports Academy.
- Solar thermal systems.
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