Proper waterproofing begins with specifications during the planning phase of a project. Every party who has an interest in the project needs to approve of the systems to be employed: Architect, Engineers, Material Suppliers and the Owner's Representative.
Waiting until the project is in progress is too late to begin researching compatible systems. Letting a subcontractor show up with a "bucket of stuff" is unacceptable.
Do not rely on a single system to provide protection from water intrusion. The roof of a house has multiple layers of protection - shingles/tiles, waterproof under layment, metal flashing and sometimes even a layer of adhesive membrane.
The cost of most shotcrete pools exceeds $50,000 and can be over a $1M... so why wouldn't you protect the concrete and reinforcing steel from water intrusion from both sides?
Protect both sides
Water can permeate concrete from both sides - the inside containing the water and from water in the soil. Basement walls are waterproofed on the outside because ground water weeps through concrete.
Ground water permeating into a concrete swimming pool from the outside, over time can corrode the reinforcing steel. The steel expands as it corrodes, causing the concrete to crack. A crack allows an even easier path for water to enter the concrete... causing even more corrosion. This may take decades to occur, depending upon the density of the concrete and level of ground water.
If you are building an elaborate swimming pool, with living space below or an expensive glass tile mosaic interior, why wouldn't you protect both sides of the concrete from water intrusion? After all don't you want the pool to last forever?
Corruptible & Non-Corruptible Systems
A corruptible system is one that can be damaged during construction activities. A non-corruptible system is one that cannot be compromised without intense effort (e.g. jack hammering or drilling holes).
A corruptible system is usually a membrane or topical system that is applied to the surface to be protected. A non-corruptible system is one that is integral within the concrete, mixed into the cement so that it is through and through.
A combination of both of these formats is the best protection available.
Redirect the water
Attention must also be paid to directing ground water away from the pool shell, through the use of drainage mats, french drains, a layer of rock under pool and/or de-watering wells.
Keeping ground water away from the exterior of the pool will also control water migration and external hydrostatic pressures.
Placement of the waterproofing
Waterproofing should always be installed above the highest possible water level in the vessel. It sound like common sense... but why would you terminate the waterproofing below the water level?
Making the effort to install the waterproofing above and beyond the maximum water level, will also provide some protection from wave action, splashing and efflorescence. After all, pools don't sit as reflection ponds - people swim in them!
Paolo Benedetti, SWD Aquatic Artist, Watershape Consultant, Expert Witness, International Construction Management
Contact the author at: firstname.lastname@example.org or 408-776-8220 "Creating water as art."™
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