Over the years the action of the tides and the waves of passing river craft had eroded the blocks of this seawall at Drummoyne on Sydney Harbour.
Gaps had developed between the twenty-six metres of sandstone blockwork and more and more fines were being washed out by the action of the water.
The spaces between the blocks had been gradually enlarged until some were quite big gaps. This continuing erosion could have eventually destroyed the wall itself if it were not attended to.
The well-known Apees Marlan Company was contacted by the property owners. Having devised the best way to rectify the problem, John Jarvie of Apees Marlan called in the team from Uretek under the direction of Steve Williams, Uretek's senior area manager.
The Uretek Operations technicians drilled and inserted injection tubes all along the frontage about half a metre behind the wall. By injection of Uretek patented structural resins, the voids were filled at various depths. Then extra pressure was exerted by injecting more expanding resin to plug the holes between the sandstone blocks.
Great care was taken to avoid any tendency to push the wall outwards, because Uretek resins can produce very substantial pressure.
Williams explained that in repairing voiding in seawalls the Uretek method has some great advantages over concrete.
"Firstly with Uretek there's no excavation," he said "that'd be laborious, time-consuming and perhaps even dangerous, as the water could rush in, or even push the wall.
"Secondly the expanding Uretek resin seals itself instantly, so that it does not mix with the water. And being light, it stays on top of the water in the void, pushing the water down and out. Then the Uretek resin plugs the wall cracks so that the water can't return.
"On the other hand, concrete poured into the voids would sink to the bottom, mix with the water and be weakened and perhaps sucked out into the river or canal.
"It's also important and reassuring that the injected Uretek resin is completely inert, environmentally neutral and will not leach out into the waterway.
"Frequently the area behind seawalls sinks down due to the voids developing down behind the walls. If that has happened, Uretek expanding resins can bring such areas back up to their proper levels while the voids and gaps are being treated."
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