Swimming pool vessels are intended to hold water without leaking. Therefore regardless of the materials of construction, success is measured by having a watertight vessel across all surfaces, joints, and penetrations. The effect of a swimming pool leaking water could be minimal or catastrophic.
Waterproofing through materials of construction: The structural design of the concrete in a concrete swimming pool affects the water tightness of the pool structure. A design solution to ACI-350 standard, which is the standard for concrete structures intended for conveying, storing, or treating water, wastewater, or other nonhazardous liquids, provides additional steel within the structure above the requirements found in ACI-318 which is the building code requirement for structural concrete. The additional steel in the pool shell limits the concrete shrinkage during curing and minimizes the formation of cracks in the pool shell. There will be shrinkage cracks in the shell, but none through which water may travel. Pools constructed from stainless steel are waterproof due to water not being able to pass through metal, but the design and installation of joints is crucial as many panels are formed together to create a pool. All joints or penetrations must be field assembled as required by the manufacturer of the pool system to create a watertight pool.
Waterproofing after pool vessel construction: A concrete vessel can be waterproofed after construction in a handful of ways. Waterproofing with a cementitious product provides a compatible material on which to apply pool finishes. Rolled on sheet goods and/or liquid waterproofing systems may be appropriate for some types of pool finishes, but may not be appropriate for all pool finishes. Admixtures to concrete or spray on products that create crystalline structures within the concrete may create adherence issues between the concrete and pool finishes. Spray on waterproofing products that do not create crystals but penetrates the concrete may be appropriate for use with concrete pool shells. It is recommended that whatever waterproofing system that is to be used is verified with the manufacturer for use with the pool finish. PVC liners are used in stainless steel pools and as a liner in existing concrete pools to provide a waterproofing surface above the pool structure. The PVC weld joints must be complete and all penetrations firmly installed to create a fully watertight liner.
The finished swimming pool inclusive of the structure, waterproofing and finishes must be a solution that is compatible and holds water in the pool. Proper installation and compatibility between components is key to having a pool that is waterproof. Anything less will create ongoing issues that are costly and time consuming to address on a remedial basis.