We were recently brought into a commercial renovation where rust stains kept appearing through the pool’s interior finish. At first glance, it looked like a cosmetic problem. But the moment demolition began, it became clear the issue ran far deeper. Beneath the surface we found extensive corrosion throughout the reinforcing steel — the result of years of water migration, poor material selection and a lack of proper waterproofing.

This project illustrates something clients rarely see. Pool failures do not happen suddenly. They develop slowly, often invisibly, and by the time symptoms appear, the structure beneath may be severely compromised. It is a reminder that aquatic engineering is not optional. It is the difference between a long lasting vessel and a catastrophic failure that costs hundreds of thousands or even millions of dollars to repair.

When Natural Stone Becomes a Structural Liability

One of the first failures we identified occurred at the perimeter overflow edge. Water continuously moves across this sloped stone surface before dropping into the grate and gutter below. This means the surface is exposed to water for long periods of time and then left exposed to air when the system cycles off. Any material placed in this location must perform under those conditions. If it does not, the overflow edge becomes a direct source of moisture intrusion.

Natural stone was used at this overflow edge, which is where the problem began. Architects and designers often specify natural stone because it is visually beautiful and provides texture and warmth that manufactured materials cannot replicate. The issue is that most natural stones are porous, and in an overflow system they absorb water every time the pool is operating. That moisture then moves into the setting bed and remains trapped behind the stone. Over time this trapped moisture leads to calcification, staining and the early stages of delamination as the bond weakens.

Some try to manage this with topical sealers, but sealers break down quickly in aquatic environments. Pool chemicals degrade them, sunlight degrades them and constant water flow wears them away. Once a sealer fails the stone returns to its natural porosity, and the trapped moisture and deterioration continue as if the sealer were never there.

As water moves through porous stone, it pulls out natural minerals contained within the stone itself. When the water evaporates, those minerals are left behind as visible residue. This shows up as efflorescence, a white powdery film, or as iron-based staining, which appears yellow, orange or brown. Both conditions are clear warning signs that water is moving through the stone and not remaining at the surface where it belongs.

To prevent this, perimeter overflow edges should use extremely dense stones like granite or fully non porous materials such as porcelain or tile. These materials do not absorb water and therefore prevent moisture from reaching the setting bed or any structural components below, eliminating the long-term risks associated with porous stone in this location.

Understanding Concrete Porosity & Structural Quality

In this case the moisture that passed through the stone did not stop at the setting bed. Because the bond beam had no waterproofing layer, the water continued migrating into the concrete itself. Once inside the concrete it moved through the material until it reached the reinforcing steel, where deterioration began.

That movement is possible because concrete is naturally porous. Even high-quality concrete contains networks of tiny voids and capillaries that can draw in and transport moisture. When that moisture eventually reaches steel reinforcement, corrosion starts. As the steel corrodes it expands, creating internal pressure that fractures the surrounding concrete. Those fractures then create new pathways for water, allowing the process to speed up and spread.

Concrete quality determines how easily this can happen. Lower-strength mixes have a more open internal structure, which allows moisture to move more freely. Higher-strength mixes are much denser, limiting permeability and slowing the rate at which water can travel. Around 5,000 psi, concrete becomes significantly more resistant to water penetration, offering a measure of protection when incidental moisture is present.

This is why building codes dictate minimum concrete requirements for pools and water-retaining structures. Codes like ACI 318 (Building Code Requirements for Structural Concrete), ACI 350 (Environmental Engineering Concrete Structures), and state-specific pool codes require concrete to meet defined strength, durability and permeability standards when it is used to contain water. These codes recognize that pool structures are exposed to constant moisture, hydrostatic pressure and chemically treated water, all of which accelerate deterioration in lower-quality concrete. For these reasons, a 5,000 psi minimum mix is required for pool shells and other aquatic structures to ensure long-term durability and protection of the reinforcement.

These requirements exist for situations exactly like this one. A porous finish material at the overflow edge introduced moisture into the assembly, and without a waterproofing barrier there was nothing to stop that moisture from entering the concrete. Even when the concrete itself meets strength and durability expectations, the absence of a dedicated waterproofing system leaves the structure vulnerable. Once water finds a pathway inward, it will continue moving through the assembly until it reaches components it should never contact. This is why proper waterproofing is not optional in aquatic construction — it is the protective layer that prevents a localized moisture condition from becoming a structural problem.

Even when concrete meets strength and durability requirements, it cannot stop moisture on its own. Without a waterproofing layer, any water that penetrates the finish materials has a direct path into the structure. That is what allowed moisture in this project to move past the stone and into the bond beam. Waterproofing is not always required by code, but it serves as the critical barrier that prevents a surface-level moisture condition from becoming a structural concern. This project is a clear example of how the absence of that barrier can allow a small vulnerability at the finish to develop into a deeper issue within the vessel.

Waterproofing

In underwater and wet-dry applications, and especially in commercial work where liability and long-term performance are critical, waterproofing the pool shell is always a smart investment. While codes may not require it in every situation, we specify waterproofing on ALL of our projects regardless of concrete strength because it provides a dedicated barrier between the finish materials and the structural components of the vessel. It is the most reliable way to control moisture movement and protect the reinforcement from unintended exposure.

This project is a clear example of what can happen when a vessel is left unprotected. No waterproofing was applied to the bond beam, so the moisture that passed through the porous stone and setting bed continued directly into the concrete. With no membrane to stop it, the water entered the capillaries of the concrete, reached the reinforcing steel and initiated the corrosion process that led to the structural deterioration we uncovered.

Had a waterproofing system been in place, the outcome would have been different. Moisture migrating through the porous stone would have stopped at the membrane instead of moving into the structural shell. In that scenario the water would have pooled beneath the finish material, which can still lead to issues such as bond loss, calcification or localized delamination. Those are service-level problems that require repair but do not compromise the structural integrity of the vessel. What occurred here was far more serious because the moisture was able to bypass the finish entirely and affect the structure itself.

Waterproofing does not eliminate the need for correct materials at the overflow edge, and it does not replace high-quality concrete. But it provides a critical layer of defense that prevents an isolated moisture condition from developing into a structural failure.

Compounding Factors That Led to Failure

In this case several independent missteps worked together to create the conditions for failure. A porous finish material allowed moisture into the assembly. The absence of waterproofing gave that moisture a direct path into the concrete. Once it reached the reinforcing steel, corrosion began.
Each step in the sequence could have been prevented, yet together they created a failure mechanism that would only worsen with time.

Why Oversight Alone Is Not Enough

In the construction world, roles are often divided.
Architects specify finishes.
Engineers design the structure.
Contractors build it.

The problem is simple.
None of these disciplines are trained specifically in aquatic environments.

A structural engineer may be excellent at buildings, parking structures or bridges, but pool vessels are a different category entirely. They involve
• constant chemical exposure
• continuous water pressure
• specialty waterproofing
• material interactions unique to aquatic environments

Architects can specify beautiful materials that perform perfectly on a façade but fail when submerged. Builders may follow drawings exactly, unaware that a small detailing error can lead to structural damage a few years later.

This is why aquatic engineering exists. It fills the gap between architecture, structural engineering, waterproofing, construction and chemistry. Without this specialization, even well intentioned teams can miss issues that eventually turn into major failures.

At Smart Aquatics, we bridge these disciplines. We understand how concrete, stone, waterproofing systems and pool chemistry interact so that each part of the vessel supports the others instead of compromising them.

What True Remediation Actually Involves

When reinforcement inside a pool shell begins to corrode, remediation becomes a structural repair — not a cosmetic one. It cannot be solved by patching plaster or applying new finishes.

Proper remediation requires:

• removing all interior finishes
• exposing all affected reinforcement
• demolishing and replacing compromised rebar
• rebuilding structural sections with appropriate concrete mixes
• applying hydraulic cement where required
• installing a fully integrated waterproofing system across all surfaces
• pressure-testing and verifying watertightness before finishes are reapplied

Once a specialist begins structural remediation, they assume responsibility for the vessel moving forward. This is why shortcuts are not an option. Any failure after remediation becomes the liability of the firm who performed the work.

This level of accountability demands the same rigor and precision as new construction. Structural renovation is not simply about restoring appearance. It is about reinstating the integrity and longevity of the vessel so it performs reliably for decades.

Preventing Failures Before They Begin

Every issue uncovered in this project was preventable.
Each failure began as a small oversight.
And each oversight escalated because no aquatic specialist was involved during design or construction.

The cost of correcting these failures far exceeds the cost of building the vessel correctly from the start.

This is why Smart Aquatics exists. We combine aquatic engineering, construction knowledge and material science to ensure every pool and water feature is designed, engineered and built for long-term performance.

Protect your investment by involving specialists who understand the unique demands of aquatic structures.