Corrosion is only one of the destructive forces acting in and
around waterparks and aquatics facilities. But it can be very
frustrating for pool operators, and perhaps a little confusing for
pool designers and building architects. Selecting appropriate
materials and finishes is critical during the design process.
Operators must understand their pool and building systems,
particularly as they relate to corrosion protection of materials
We’ve all experienced the dreaded appearance of rust spots on
our stainless steel ladders and gutters, but corrosion around
indoor pools goes much deeper. With the advent of water
slides, multiple sprays, greater surface areas, and warmer water,
corrosion potential is greater than ever.
All the attractive play features and the shallow, zero-depth pools
mean that attendance is greater and the moisture loading on
dehumidification systems is greater than ever. Perhaps the most
helpful design criterion is the ventilation system capacity for
fresh air. ASHRAE says to design a natatorium system so that up to
30 percent of the recirculation rate can be brought in as fresh
air. We recommend greater fresh air capacity, 50- to 100 percent
Stainless steel often is a disappointing material because the
expectation is that stainless means no corrosion or staining.
Unfortunately, stainless steel is subject to staining, corrosion or
even failure under the right conditions. Dozens of stainless steel
alloys exist, so choosing the right alloy during the design process
can be very helpful.
Perhaps the most catastrophic and hidden corrosion danger is the
use of stainless steel cables or rods to support a ceiling over a
pool area. Several structural failures over pools have led to
sudden collapse of ceilings, along with deaths and injuries. The
cause was chloride-induced stress corrosion cracking (SCC).
Common stainless steel alloys in tension are subject to SCC due to
water vapor from a pool. The structural designer must choose the
appropriate stainless steel and related materials for the pool
All of the materials used to build an indoor pool and the building
enclosure are potential corrosion targets as well, with a few
exceptions. Plastic, glass, tile, stone, masonry and concrete
typically resist corrosion quite well. Carbon steel, cast iron,
ductile iron, copper, bronze and aluminum are all subject to
varying degrees of corrosion, depending on how they are used.
Carbon steel, cast iron and ductile iron can be coated with paint,
but this is typically a short-lived protection. Copper will show
green corrosion resulting from chlorine in the air. Red brass and
bronze typically resist pool corrosion well. Common aluminum alloys
are poorly suited for submergence in pool water, but they perform
quite well above water as door and window framing.
Pool chemicals can quickly deteriorate the filter room structure
and the water treatment equipment. Acid, in particular, is a
challenge regarding corrosion. An uncoated steel bar joist roof
structure will corrode quickly, creating a maintenance headache.
Other metal materials in the chemical room also will quickly
corrode. The answer is to ventilate the chemical and filter room
air to the outside. Fiberglass and plastic materials also must be
Metal buildings are occasionally considered for pool enclosures.
The corrosion potential with an indoor pool environment will
definitely challenge a metal building, requiring extensive coating
protection and ongoing coating maintenance.
Galvanizing is one method of trying to protect steel in the pool
air environment, with typically poor long-term results. A thin zinc
coating is not adequate. Even a hot-dipped galvanized coating will
have a limited life in the filter room for a pool. Stainless steel
or aluminum air ducting is acceptable. Fiberglass doors and PVC
piping are appropriate for most pool area applications. PVC
electrical conduit is corrosion resistant and can be painted for
Something new to some designers and operators may be the growing
use of “salt systems” for disinfection. The pool is
dosed with 4,000 ppm of salt and an electrical unit is used to
create chlorine within the piping system. This disinfection method
is gaining acceptance, particularly for smaller pools, but can
cause new corrosion problems. Items at risk include some heater
cores that are not nickel aluminum bronze, and underwater lights
with the wrong bronze alloy. Adequate electrical bonding is a
must with salt pools.
Sacrificial anodes are recommended as well. Most designers have an
understanding of the above-mentioned materials. As with many things
in life, the challenge is in applying them effectively. As pool
systems and equipment continue to evolve, the potential for pool
corrosion will continue to challenge our ability to use the right
materials to resist the damaging effects of corrosion.