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Encyclopedia > Construction methods for private pools

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In-ground pools

There are several distinct methods of producing a private home swimming pool: Concrete, "Vinyl Liner" and Fibreglass types. All construction types have individual benefits and very few problems, the choice being generally up to the individual purchaser. Concrete pools have many different construction methods, and the term "concrete" describes the basic materials used in construction. Vinyl Liner pools describes the method of lining the interior, not the construction materials, and Fibreglass refers to the base material of the pool shell. As these terms refer to different parts of the pools the names may be confusing to the newcomer to the swimming pool world.


Concrete Pools

Types of concrete pools

Concrete pools may be constructed using many differing methods.


Concrete Block

In concrete block construction (AKA - UK "Breeze Block" US "Cinder Block"), a floor foundation is poured and a concrete "wall" structure is constructed to the desired shape of the pool. Filtration attachments are inserted into the walls, which are generally reinforced with deformed steel bars, and "solid poured" (the internal cavites are filled with concrete). Once the shell is completed, the pool may be rendered internally by coating a slurry of cement/white crushed marble, fitting a PVC Vinyl waterproof liner, sprayed with a fibreglass strand-reinforced resin coating, or even just painted. Due to various the internal finishes, this pool could also be variously described as a "vinyl-liner" pool, or "fibreglass pool".


Poured Concrete
A poured-concrete residential pool in Mexico

In poured concrete construction, a mold is created using (typically) wood or plywood, which will encase the finished pool shape. Usually the pool floor is poured first, them the wall molds constructed on top of the floor, connected via steel Re bars left protruding from the floor. Steel reinforcing rods (AKA "Re Bars") will be inserted, then the cavities in the molds are filled with high-density (25 mpa) pool concrete. A vibrating tool is used to ensure the concrete fills all the cavities. Once the concrete has set, the molds are removed. The internal of the pool can be coated as in concrete block construction. Image File history File linksMetadata Download high-resolution version (1024x683, 519 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Swimming pool Metadata This file contains additional information, probably added from the digital camera or scanner used to... Image File history File linksMetadata Download high-resolution version (1024x683, 519 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Swimming pool Metadata This file contains additional information, probably added from the digital camera or scanner used to...


Gunite pools

In Gunite pool construction, a "Timber Pool" is first created in wood or plywood inside the excavated pool shape and size. This "temporary pool" is made larger than the desired finished pool by the thickness of the walls - usually 6" to 8" (150mm to 200mm) in width. This temporary pool wall is termed "the boxing" in the swimming pool industry, and must be substantial as the following procedure will indicate. The internal area of the "temporary pool" is now lined with Re Bars at a pre-determined distance apart. This will vary due to local by-law requirements, but typically will us 3/8" to 3/4" (10mm to 20mm) deformed steel bars at 8" to 10" centers (200mm to 250mm) in a square grid pattern. This is suspended away from the "boxing" (wood formers) by "stand-offs" a device 2" to 3" (50mm 60mm)long which keeps the reinforcing steel centered in the completed wall and way from the bottom of the (drainage material layered) excavation. After allowing for the pool recirculation system devices to be allowed for in the finished wall and floor, the entire interior is pneumatically sprayed with a slurry of cement, pool gravel mix, and water. What distinguishes the name "Gunite" is that the mix is delivered pneumatically down a 4" (100mm) hose as a dry mix under pressure, terminating at the "spray head" or nozzle where water is added by the operator. This is a vital part of the procedure, as the ingedients must be mixed in a critical percentage, or the resulting concrete will lack strength. For this reason, Gunite pool walls are usually thicker than other methods which will be addressed in this article. The consistency of the mix is measured in "slump" i.e. an upturned "witches hat" of the mix is allowed to "slump" as a meeasure of how it will "stick" to the vertical Re bars. 4" (100mm) slump is common in these pools. Once the concrete has been placed into the pool, the interior is "straightened" by a team of operatives who use steel formers and trowels ("Floats") to straighten the interior walls. (The exterior walls are held in shape by the "boxing"). Particular attention is taken to the top 12" (300mm)of the pool as this is typically where a row of Mosaic Tiles will be fitted in the final phases of the pool construction, but the majority of the interior is left in a relatively rough state as it assists the adhereance of the final interior plaster finish.


Shotcrete

As with "Gunite" pools, "Shotcrete" describes the final stage of the pool construction: the application of the concrete. As in gunite pools, a timber pool is first constructed in timber or plywood, then the reinforcing steel, filtration etc. equipment allowed for, then finally the application of the pool concrete. Whereas gunite strength is determined by the nozzel operator, shotcrete arrived in a cement truck "ready to use" from the batching plant. Quality is determined by the strength ordered. 25mpa (megapascals - 3600 psi) is typical and guaranteeed by the batching plant. Applied by pneumatic pressure through a 2-1/2" (60mm) diameter hose, the nozzel operator has no influence on the strength of the resulting concrete. By eliminating the unknown factor of gfunite, shotcrete pool walls are typically 4" (100mm) thick and use a lesser amount of concrete yet provide superior strength per volume. As in gunite pools, the shotcrete pool typically has a row of mosaic tiles at waterline, and an internal plastered finish of white cement/crushed marble generically referred to in the USA as "Marblesheen".


Both methods of applying the concrete needs special attention to the application, as the re bar mesh provided a barrier that may lead to cavities forming immediately behing the rods, or "rebound" where the stones in the gravel mix re-bound off the temporary pool boxing creating a differential in concrete strength. The skill of the shotcrete operator is not required to be as high as the gunite nozzle man, but both operators must be experinced and aware of potential strenght issues if the concrete is not placed as required by the pool's designer. Once the pool concrete has set (14 days to reach 85% strength) the boxing may be removed. Usually this damages the timber or plywood and it is not able to be re-cycled and goes to a land fill. The exterior of the pool wall is then infilled with (typically) drainage material.


Emptying of concrete pools

Concrete pools are not dissimilar to concrete boats: i.e. they are a contiguous shell that will "float" under certain circumstances. It is therefore essential that an unrestricted "hydrostatic valve" (AKA Hydro Valve) is incorporated in the pool design. It is not advisable to empty these pools unnecesarily - especially in rainy months - as you are wholly reliant on the operation of the hydro valve to avoid flotation (and possible destruction) of the swimming pool. The emptying of all pools must be conducted strictly under the supervision of the pool builder or an authorized consultant.


Vinyl Liner pools

As mentioned above, "vinyl liner" refers to the interior finish of the pool, as PVC Thermoplastic vinyl may be used as the waterproofing membrane in a number of pool types. Generally, however, in the USA this pool type is considered to be a pre-fabricated in-ground steel-walled kitset style pool fitted with a vinyl liner (AKA Packaged Pool, VIP pool - "Vinyl Interior Pool") that can be installed in a week or so and will provide a durable, long lasting product that should last for several decades. Introduced to the public first in New Jersey in 1950 by Cascade Industries Incorporated (C.1950 - 1980), the first package pools were sold by promoter Ed Gorman through the 1951 Sears Roebuck catalog as a do-it-yourself project. In the years since then many manufacturers all over the world have produced "vinyl" pool kits that can be transported to sites and installed in a few days. Designs range from simple pre-fab galvanised steel walls to concrete "sacrificial" shutters that remain in place once the concrete has set, as opposed to the plywood boxing of gunite & shotcrete pools that is subsequently removed. Vinyl liner pools are popular with many pool buyers due to lower initial cost and the many patterns and colors available, and with users in the fact that the liners do not support algae growth and have a child friendly embossed non-slip finish. Most PVC Thermoplastic in-ground vinyl pool liners come in .20" and .30" (.50mm & .75mm)gages and are re-cyclable when the reach their design life (usually 20 to 25 years in moderate climates). Replacement liners can be installed in one to two days, and providing the basic pool shell is of substantial construction, can be changed several times over the expected life of the pool, which could be as much as fifty years or more in the case of a concrete base shell.


Fibreglass pools

Concrete pool shells may be "fibreglassed" on site, and purpose-built structures can have the on-site fibreglass finish installed, but the common understanding of a "fibreglass pool" is a one-piece molded shell which is colored blue and incorporates internal steps and seats. These shells will have typical pool filtration and lighting, and may be installed in one to two days after the excavation has been completed. Typically these pools have a roll-over top, but standard pool copings or a pool deck may be added. As mentioned in the concrete section, these pool also can be suceptible to floatation, and must not be emptied without reference to the supplier - even though a hydro valve has been incorporated.
Fibreglass pools are PVC Thermoset in composition (ie the chemical reaction involved in "curing" alters the structural elements of the PVC) and consequently they cannot be re-cycled once they have reached their design life.


Above-ground pools

Above-ground pools range from simple 15' (4.8m) circular "splashers" with 2' 0" (600mm) walls, to fully equipped 16' x 32 ' (4.8m x 9.6m) models complete with decking, filtration, lights and chlorination systems (which cost nearly as much as entry-level in-ground pools).


Often available as a kitset, many are installed by the home owners themselves, although most pool shops will have a list of Contractor's names who will do the job for a fee. These pools typically comprise 4' 0" (1.2m) tall metallic walls (typically Aluminum, or corrugated .30" (.75mm) rolled steel), often designed to form a circular shape, oval or rounded-end rectangles are common. A .20" (.50mm) flexible PVC Vinyl liner, powder-coated aluminum copings and some form of filtration complete the package. The exterior of the walls are typically painted to resemble timber or masonry designs, or may have a swimming-related illustration (dolphins, fish etc.) screen-printed on them. These pools are non-structural, the design working due to large radius or circular shapes, which equally distribute the stresses generated by the water contained within. The strongest design of these pools being the circular or round pools, which require no additional external bracing to maintain their shape. The rectangular or oblong designs generally require substantial bracing or butresses at intervals along the straight sides, and a connecting strap or beam under the pool floor (the floor usually comprising trowelled sand, or an 10:1 sand/cement mix) to tie the braces together and prevent the pool shape deforming.


Although sometimes desired, it is not advisable to install these pool types "in the ground", as the design does not allow for external forces - such as backfill - to be placed against the wall exterior due to possible premature corrosion of the walls, and internal collapse of the walls if the pool water is removed. These walls are not usually strong enough to withstand the weight of the back-fill and would collapse inwards. If an "in-ground" look is desired using these pools, the best method would be to proved a larger excavation that would allow the pool to be constructed within with adequate clearance from the surrounding soil (a 45 degree stabilized slope would be preferable) then the resulting large excavation decked over to the pool edge to simulate ground level.


Due to the height of the walls relative to surrounding ground level, these pools are usually supplied with a PVC Injection molded step ladder which straddles the pool wall, allowing access and egress. These are removable, and should be taken away from the pool when not in use, as a safety measure to eliminate access by unsupervised young children.


These pools usually have a basic filtration system comprising a small hi-rate sand or cartridge type filter and "flooded suction" water pump and basic chlorination system (often a floating or tablet tri-chlor feeder device).


 
 

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