Why build reefs?

By Lawrence Cardosa
Photo by Reef Ball Asia

Man’s activities and natural disasters have led to a reductions in our natural reef systems. Recreationally, growth in sports fishing, scuba diving, and boating has increased the pressures on these systems. Commercially, our seafood industry is dependent on developing the ocean to enable ever larger, yet sustainable, harvests. The loss of our natural systems, coupled with increased use, compels us to do everything we can to save natural reefs. Even so, the natural reefs cannot rebuild themselves fast enough to meet human demands. Long lasting artificial reefs are useful tools for restoring our reef systems to a natural and productive balance.

What’s involved

Reef Balls are made by pouring concrete into a fiberglass mold containing a central Polyform buoy surrounded by various sized inflatable balls to make holes. Six mold sizes are available. Any type of concrete can generally be used, including end-of-day waste, but additives are needed to give the Reef Balls high strength and to make the concrete suitable for marine life growth.

Floating deployment

Reef Balls are cast around an extremely durable Polyform bladder. This bladder can be left in the unit to provide flotation so the Reef Ball can be towed behind any size boat. Once at the site, the bladder is deflated and removed. When divers are used, the unit can be placed precisely on the sea floor with a controlled descent, making repairs to damaged reefs possible without endangering natural reefs.

Unique hole sizing & placement

Natural reefs are variable in size, shape and hole density. Artificial reefs function better when they mimic nature. The balls which create holes are inflated to different pressures to vary hole sizes. Interconnected holes are possible by inflating the balls until they touch.

Surface textures

A variety of surface textures that enhance the settlement of marine life are available. A popular surface texture is made by spraying sugar water onto the surfaces of the mold before casting. After the cement mixture hardens, the mold panels are removed and the last 1/2 inch of concrete remains unhardened. A rough stony surface is exposed by rinsing the module with a garden hose. All surfaces are enhanced by the use of an air entrainment admixture. This non-toxic, soapy-like additive creates tiny pockets in the concrete which pits the surface of the Reef Balls. These pits offer tiny marine organisms (such as larval corals) a place to easily attach themselves.


Reef Balls are designed so that over half of the weight is in the bottom near the sea floor. All sizes of Reef Balls have withstood, without movement, heavy tropical storms in as little as 20 feet of water without anchors. Reef Balls are stable because the opening in the top of the unit breaks up the lifting force of the hydrofoil effect common to dome shapes. Side holes are wider near the center of the walls and narrow near the units surface. This feature creates miniature vortexes which further reduce lifting forces and bring rich nutrients to life on the reef.

Marine friendly concrete

The concrete used to make Reef Balls features W.R. Grace’s Force 10,000 micro silica to create a super high strength, abrasion resistant, concrete that has a pH similar to natural sea water. This is unlike regular concrete which has a surface pH as high as 12. This high pH (the sea has a natural pH of 8.3) can inhibit the settlement and growth of many species of marine life including some larval corals. Micro silica gives Reef Balls an expected life of 500 or more years.