The most common type of in-ground manufactured swimming pool on the market today is the concrete pool. Although there are a wide variety of manufactured pools on the market (concrete, fiberglass, and vinyl), concrete pools represent 60% of pools being built today. Concrete pools offer limitless options for shape, configuration, and spa features. The excavation site is reinforced with steel and provides a sturdy support for pools of any shape or size. Fiberglass pools are manufactured in a factory and the prefabricated pool arrives at its destination and is set in a previously excavated site. Fiberglass pools constitute 7% of the market and are limited in the variety of shapes available. Vinyl-lined pools arrive in a kit with construction completing at the site and represent 33% of the pool market. A custom fit vinyl liner is installed after the decking is completed and the structure is then filled with water. Previously limited to geometric designs only, free form options are now available.
In the design and manufacturing of pre-fabricated aboveground pools, the cost of fabrication continues to be a major concern. Pools have to be manufactured in a variety of styles and sizes to accommodate the available space requirements of the customer and the variety of components necessary for manufacturing is quite large. Designs that can incorporate this flexibility and reduce the necessary inventory required to accommodate a variety of sizes and structures have begun to arrive in the above ground swimming pool manufacturing marketplace creating easier systems to erect without sacrificing stability.
Above ground swimming pools have an exterior wall of machined sheet metal construction formed into a continuous circular or oval shape. Support or reinforcing posts are located around the perimeter of the pool and serve to strengthen and maintain the pool wall in the desired position. Conventionally, various components make up these post assemblies and may include upper and lower rails for engaging and covering the upper and lower edges of the metal pool wall, some form of plate connectors which serve to mount the vertical posts in position and which may also be used to secure sections of ledges around the top of the pool wall. Some form of cap is usually fastened to finish the top of the post assembly.
Above ground pools consist of a sidewall, a water-impermeable liner, and a frame or superstructure for supporting and reinforcing the sidewall. The frame assembly generally includes a lower rail and a top rail to which the pool sidewall is attached. The liner is attached to an inner surface of the pool sidewall along an upper edge.
Swimming as an organized activity goes back as far as 2500 B.C. in ancient Egypt. Actual swimming pools were invented in the first century B.C. by the Romans. In Rome and Greece, swimming was part of the education of young boys. Many of the Roman pools were also heated using water diverted through piping from natural springs. The elaborate bathhouses built with marble and expensive gilding were very popular with the elite society but the majority of people continued to swim in lakes and rivers. These bathing pools were the precursors to modern day swimming pools.
In Europe, many people refrained from building swimming pools due to the fear that infections could be caught from infected swimmers. Europeans formed their first swimming organization in 1837 in London, which by then had six indoor pools. The popularity of swimming pools did not begin to increase until after the first modern Olympic games in 1896.
Raw materials for manufacturing swimming pools consist of polyvinyl chloride (PVC) plastic, galvanized steel or metal, fiberglass, concrete, and polyurethane foam. Adequate steel bars for reinforcing a concrete pool range in size from 0.38 in (0.97 cm) to 0.75 in (1.9 cm) diameter (these values vary depending on the structural requirements of the design). All piping used for pool plumbing is a minimum of schedule 40 PVC or the equivalent and must be stamped with American Society for Testing and Materials (ASTM) approval. The liners are typically plastics or similar materials.
The variety of designs for swimming pools are a reflection of the unique spatial and economic concerns of the consumer. Concrete pools are the most flexible with the ability to create any shape or configuration. Vinyl-lined pools are evolving into free form designs that can incorporate a larger variety of design options with fiberglass pools having the most restrictive design elements (one-piece construction designed at the factory). Design drawings are completed showing the actual layout of the pool, including shape, elevation, and size. An engineer provides soil and structural analysis assisting in the location and optimal design for a swimming pool installation.
Soil analysis is performed on all surfaces prior to installation to ensure a structurally sound pool. A pool also needs to have a system that circulates the water from the bottom of the pool to the surface to help in the quality of the water. All pools must use grounded wiring and have breakers that protect from shorts in under water lighting systems.
The following is the manufacturing process of a vinyl-lined concrete pool.
- The drawings and designs of the pool are completed as the first step in the process of pool installation. After determining the grade level of the pool the site is excavated.
- The excavation is 3 ft (91.4 cm) outside of the actual pool dimension to allow a working area around the pool. First, stakes are driven into the four corners of the pool area. The stakes are 2 × 3 in (5.1 × 7.6 cm) and sharpened at one end. Next, a second set of stakes is driven, outlining an area 6 ft (1.8 m) larger than the pool.
- An experienced worker uses a bulldozer to excavate the earth in the site of the pool. The excavation needs to be level so a transit level is used. During excavation 2 in (5.1 cm) is allowed for bottom material. The bottom is smoothed using sand, vermiculite, cement, grout mix (sand and cement), or stone dust. The bottom must be a smooth surface as this is where the liner rests. The size of the pipe is determined by calculating the volume of water in the pool and varies depending on the holding capacity of the swimming pool.
- The wall of the in-ground swimming pool is made from a continuous length of machined fiberglass sheeting. The walls are lowered into the excavation manually beginning with the corner sections. The subsequent wall panels will be self-supporting as each additional panel is added. They are installed working in two directions placing panels with machined holes for light and skimmer in their appropriate places.
- A steel rod driven through the hole in the bottom of the panel fixes the positions.
- The bottom circulation or main drain is connected to the suction side of the pump and motor. Two 1.5 in (3.8 cm) plugs are installed into the bottom threads of the main body of the drain. Duct tape is used to cover the drain to keep dirt and/or bottom fill from getting into the gaskets or faceplate.
Next, the pipe is dug below the existing grade and under the panel wall.
- After installing the main drain the walls and corners are rechecked for level alignment and squareness. A concrete collar is poured around the perimeter of the pool at the base of the walls to secure the pool in place. The collar is made from a thin concrete mixture about 6 in (15.2 cm) deep around the pool wall. After the concrete collar is dry (about 24 hours) the bottom can be finished.
- The concrete bottom is poured, either pumped from a truck or by a method called gunite. Gunite pumps dry cement and sand through a hose adding water at the nozzle.
- Vermiculite and cement or grout provide a permanent bottom and is installed by an experienced mason. Plumbing is installed before backfilling. Black poly (coil pipe) or PVC schedule 40 pipe is placed along the top of the concrete collar.
- The pipe is run from each fitting (skimmer, main drain, return) back to the filter. Pipe compound or non-hardening permatex is placed on the thread of the adapter.
- Two pipe clamps are slipped over the end of the pipe and the pipe is pushed over the end of the fitting. Tightening clamps will set in approximately 15 minutes.
- After the vacuum has cleaned the area, water is added. If large rocks are used for the backfill, the pipes are covered with sand to prevent damage.
- Once the pool has been filled with water all the equipment should be turned on. Chemicals such as chlorine, muratic acid, and stabilizer will need to be added. The filter system should be run continuously the first 24 hours until the water reaches the desired level of clarity. This typically represents the time required for 99% of the pool water to pass through the filter. Usually, once this level is reached the pool can run as little as six hours a day to maintain a healthy environment. The surface of the water usually contains the most pollutants (i.e., body oils, grease, sweat, and skin debris). To keep the pool clean, a skimmer (filtering device) should draw at least 70% of the pool water from the surface for filtration and treatment.
- Water temperature has to be carefully monitored between 80.6-86°F (27-30°C). Temperatures that are too high may cause cracks in the pool structure or cause vinyl liners to expand and lose their elasticity. The higher temperatures may also destroy the polymers leaving the liner dry and brittle.
- The maximum velocity in any suction pipe must not exceed 5 ft (1.52 m) per second. The maximum velocity in any pressure pipe must not exceed 9 ft (2.74 m) per second. The Filtration Rate is the speed or velocity of the water through the filtration media. The slower the Filtration Rate, the more effective the filtration.
As soon as the ditches are dug and the piping in place, the pipes are capped and filled with pressurized water to check for stress (leaks). Electrical code inspectors check the electrical wiring systems for safety. Concrete decks and any surfaces using gunite are checked for smoothness and integrity. Since the gunite is customized to the design specifications the concrete is inspected visually on each site. The steel reinforcing material is checked after installation looking for any stress or weakness in the material.
The variety of materials used in pool construction create a large proportion of recyclable materials. Galvanized steel reinforcing grids are manufactured at the factory with scrap metal being melted and reformed for future projects. Concrete byproducts from trimming the foundations are disposed of into large dumpsters onsite and extreme care is taken to diminish waste. City water systems are used to dispose of the backwashed pool water and plastics used in the liners are carefully fabricated with excess materials being recycled.
Improvements are constantly being made in the manufacturing and construction of swimming pools. Above ground pools are using lighter weight construction and are easier to assemble. Newer materials such as a laminate of woven polypropylene mesh fabric will not burst but cause water to slowly leak from the pool. Fiber optics are being used in underwater lighting systems and provide safe alternatives to electrical installations. Automated pool systems allow in-house operation and pre-programmed timing of pool maintenance activities.
Where to Learn More
Above Ground Pools Web Page. December 2001. < http://www.above-ground-pools.com >.
Pleasure Pools Web Page. December 2001. < http://www.pleasurepoolinc.com >.
SwimCSI Web Page. December 2001. < http://www.swimcsi.com >.
The Swimming Pool Buyer's Guide Web Page. December 2001. < http://www.swimmingpoolbuyersguide.com >.
Bonny P. McClain