An electrical substation built to support a major road tunnel infrastructure project in greater Sydney required protection from gas and water leaks. The substation would contain critical electrical and mechanical services to support the tunnel’s daily operations and maintenance, including ventilation systems, once it was complete and fully accessible by the public. 

The substation was built partially underground with the inside area consisting of 790m2 of concrete floor and 150m2 of piled walls with shotcrete infill. The structure was located adjacent to an old waste disposal area known to emit methane gases from decomposing waste, and the project managers and engineers were concerned about potential gas build up. In addition, being 4m underground, there were also concerns that over time the substation may be impacted by ground water.

The project engineers sought an extremely hard wearing barrier application with the ability to mitigate water and gas leaks. Following a referral through a subcontractor’s tender, Mainmark was engaged by the project engineers to provide a suitable water and gas barrier to protect the walls and floors from future structural degradation.

The large-scale project required flexibility, with Mainmark needing to coordinate the work around key construction stages without impacting on other contractors working simultaneously on site.


The client required the supply and install of a sprayed waterproof membrane to the concrete substrates inside the electrical substation to mitigate the risk of water and gas leaks. It was important that the solution came with a 20-year manufacturer’s product warranty and was able to be applied without impacting the project’s workflow and timelines.


Mainmark was contracted to supply and install a high-performance specialised resin and coating system that would provide exceptional resistance and long-term structural protection to the substation’s floor and walls. 

The water and gas membrane system was applied in stages using two different solutions. The first solution was a waterproofing membrane for the structure’s walls and floor at specific engineered thicknesses. 

The second component to the walls was a smoothing layer which was applied underneath and over the top of the waterproofing membrane; the first smoothing layer providing a supporting substrate and the second adding a protective coating for added strength and protection. The second component to the floors was provided by a third party using a blinding slab under the membrane and a finishing structural slab over the membrane.

The two smoothing layers consisted of a superfine engineered cement solution that on application provides a water-tight grouted mass with the ability to penetrate tight joints and fissures. The superfine grout solution was applied over the rough existing shotcrete to provide a smooth base for the waterproof membrane, an elastomeric liquid rubber coating that creates a tightly sealed barrier against water, gas, methane and carbon dioxide.

The large-scale infrastructure project was the first time that this elastomeric liquid rubber coating had been used in Australia and, given the significance of the project, from the early planning phase it was evident that an innovative applicator was required to apply the product. This was the perfect opportunity for Mainmark to demonstrate its expertise, application innovation and flexibility.

Mainmark worked closely with the project management team, applying the multi-layered system across two key construction phases as the substation was being built, starting with the main floor and wall area. Several months later, a secondary treatment was applied, having first ensured the floor and wall surfaces were free of defects. An initial 25mm smoothing layer was sprayed to remove surface defects that could potentially compromise the waterproofing membrane, smoothing out any undulation, pitting, corners and edges. The smoothing layer extended to the shotcrete infill walls, lapping into the piles, headstock and floor slab to ensure total coverage was achieved. The water stop membrane and final smoothing coating were then applied over the top of the first smoothing layer.

Mainmark’s expertise and precision when spraying the specialised engineered coatings ensured the product was able to be applied quickly and easily, compared to alternative solutions such as PVC welded membranes, which can be more challenging to cover corners and different surface junctions. Mainmark’s specialised solutions successfully coated the curved and irregular surface junctions, making the application process much simpler and allowing the project to be completed on time to the client’s satisfaction. The ease of delivery, coupled with Mainmark’s expertise, also minimised over-spray, preventing unnecessary product wastage.