Limiting leaks at water storage reservoir

One method of refurbishing water industry assets is to carry out surface repairs and then apply protective coatings. An applicator of Rhino Linings Australasia, said to be the only manufacturer of spray-applied coatings in Australia, recently won the tender to repair the inside and outside of the 80 metre-diameter, above-ground, steel potable water storage tank located at the Hospital Hill Reservoir in Murwillumbah, NSW.

The tank sits on a concrete ring beam with the floor of the tank a series of concrete segments. The repair was required due to the expansion joints in the floor failing and the tank starting to leak. The joints were resealed and a Rhino pure polyurea coating was applied over all floor joints, over the ring beam and a further 500 mm up the side of the tank.

Failing expansion joint seals in the floor of a water storage tank.

A major consideration in applying any surface treatment to a structure is the requirement to minimise downtime. Dennis Baker, special projects engineer at Rhino Linings, said, “The beauty of our coatings is that they are rapid setting. We can spray them on and they cure in six seconds for pure polyurea and 20 seconds for polyurethane.”

Rhino Linings’ high-build coatings are 1000 microns thick, as opposed to paints and epoxies which might only be several hundred microns. High-build polymer coatings are also flexible, which allows them to stretch and shrink as substrates expand and contract due to temperature and ground fluctuations. The coatings are continually tested to ensure they comply with the latest standards, they contain no solvents or VOCs and their application procedures contain and manage overspray.

A Rhino Linings high-pressure, plural-component spray machine on a travel pallet, with drums in bunded sections to contain minor spills.

To prevent water or material getting between the coating and substrate, terminating grooves are cut in the floor concrete and the edge of the coating is bevelled by special termination tape. This has a wire in it, which cuts the polymer at an angle as the tape is removed. Baker said, “Applied correctly, our polymers have attachment loads of 6 to 10 MPa. The concrete substrate would give way before the coating peeled off.”

It is important to prepare the substrate properly before applying any coating. This is done by ‘profiling’ the surface of the structure to the appropriate standard. Profiling involves blasting sand or similar material at a surface under high pressure to roughen the surface, which allows the coating to better ‘key’ to the substrate.

The water tank floor showing repaired seals between concrete segments and between the steel walls and ring beam.

In repairing the water storage reservoir, the surface was given a Class 2½ blast profile as specified by the relevant Australian Standard. For steel surfaces, a Rhino primer is applied to further improve adhesion, which is then coated. For concrete, the profile used is usually between 3 and 5 according to the standard profiles established by the International Concrete Repair Institute. After profiling, a Rhino primer is again applied and then the polymer coating is sprayed on.

“Rhino Linings is committed to the development of new technologies, products and services that offer the best solutions to the needs of our customers, applicators and distributors,” Baker concluded.