How do Rust stains form in my pool and how do I fix them?

What Causes Rust Stains?

Pool rust stains (or rust spots, as it is commonly called in the industry) are caused by metal being too near the surface of a pool. To understand this, you must first understand how a pool in constructed.

A Pool’s Foundation

The first phase of a pool install is to dig a hole. It must be deep and wide enough to form the pool’s shell constructed of rebar and wire. The rebar is bent into the shape of your pool, eventually creating a shell that’s tied together with wire. Like a house’s foundation, the rebar and wire structure provides the support and shape of your pool.

Once the pool shell is formed, it is filled in with shotcrete, a concrete product. In the perfect situation, the shotcrete has perfect coverage of between 6” to 12” thick. The thickness depends upon location (e.g., walls, corners, steps or bottom) and where the rebar and wire is buried in the middle of the shell (not close to the surface and not close to the dirt underneath). If the shotcrete coverage is not adequate, then the rebar and wire may be too close to the surface. Over time, it rusts by coming into contact with water and causes those unsightly pool rust stains.

It’s important to know that very few pool surfaces are completely waterproof*. Most pool surfaces permit slow seepage outside the shell. In general, this is not a problem when the rebar is properly positioned in the shotcrete or gunite (similar material used when constructing older pools).

Repairing Pool Rust Stains

The only way to properly repair a pool rust stain is to chip into the pool shell around the rust spot. Then, the rebar and/or wire must be bent into its proper place. We then spray with Rustoleum or a similar product to prevent further rusting and patch the pool with shotcrete..

Unfortunately, finding and fixing one rust spot does not mean that other spots won’t appear a month or year later. There is no way to find or predict where the rebar and wire is too close to the shotcrete or gunite surface. You can only fix the areas currently visible with surface staining.

If you have multiple pool rust stains, this may be the best time to replaster. By removing the old material, we can apply new materials to avoid future rust stain issues.

*The only current pool surfaces that are waterproof are Vinyl and Fiberglass.