What is the definition of a water tight swimming pool?
Believe it or not, there is not agreement on how a swimming pool should hold water. The differences centers around being water tight before or after the final finish is applied to the pool shell. An example would be should the pool be water tight before it is painted, plastered or tiled? It is this writers opinion that the swimming pool owner is buying a water tight pool shell and a coat of paint or other cosmetic surface should not be considered the source of water tightness. As a result, all pools should pass a water tightness test before the final finish is applied.
This conversation gets more interesting when the shell is placed using a cast in place method or a shotcrete method. Some in the industry have taken the position that shotcrete is not waterproof, but water resistant. It seems silly that someone in the swimming pool industry would make an argument that the pool shell should be water resistant.
Fortunately, there are industry standards that speak to water-tight concrete structures. The American Concrete Institute (ACI) outlines two standards: ACI 318 - Building Code Requirements for Structural Concrete, ACI 350 - Code Requirements for Environmental Engineering Concrete Structures for liquid tight containing concrete structures. In addition standard ACI 350.1 specifically provides protocols for water tightness testing.
While methods of the concrete placement may differ, cast-in-place vs. shotcrete, the result of the hardened concrete is the same, regardless of placement technique. ACI states, Shotcrete and concrete have similar percentages of permeability for given materials and water cementitious ratios. Because the properties of the concrete whether cast in place or shotcrete are the same, they are viewed as equals. As a result, swimming pools should be required to pass a water-tightness test before the finish is applied. The ACI standard requires the pool structure have no coatings or liners in place for the test. Furthermore, ACI considers coatings on the inside of the pool protective barriers and not a waterproofing system. ACI does not consider pool coatings of paint, plaster and tile /grout to be waterproofing membranes.
What is so difficult about completing a water tightness test? Completing this test is often challenged based on schedule. Depending on the means and methods used at the site, a water tightness test can take days or even weeks in some cases. When an owner is eager to open the pool and the contractor is eager to finish the job, this investment of time is often challenged. When making this decision it is important to remember that this pool is likely to last provide in-place service of 50 years or more. Having a verified water tight pool structure will reassure the owner they are getting what they are paying for and will reduce the likelihood of ongoing maintenance problems for the facility.
So the definition of a water tight swimming pool is to have the concrete pool shell serve as the primary water-tight structure no matter how the concrete is placed.