Clarifier Launder and Weir Resurfacing

The challenge

The concrete launder and weir trough around a clarifier carries the constant wash of water running over the lip and into the trough. Over time that surface spalled and roughened, and the weir lip lost its true line. Once the edge is no longer even, the water no longer spreads evenly across the weir, so the flow channels to the low spots and the wash concentrates there. That uneven flow keeps breaking the surface down, the spalling works back into the trough, and the launder can no longer carry an even overflow the way the clarifier was designed to run.

Our approach

We chip out all the failed and spalled concrete back to a solid base and clean the launder and the weir lip down to sound substrate. Then we rebuild the lost concrete in the launder and along the weir lip with a cold-applied repair mortar, bringing the section back to profile. We reprofile the lip to a true, even edge so the water can spread across it the way it should. Once the substrate is sound and shaped, we line the wetted launder against the water with a coating that leaves a smooth surface, so the trough carries an even overflow and stands up to the constant wash instead of spalling back open.

1. Assess and mapWe survey the launder and weir to map the spalled and roughened areas and check where the lip has lost its true line.
2. Chip out and cleanWe chip out the failed concrete back to a solid base and clean the launder and weir lip down to sound substrate.
3. Rebuild with repair mortarWe rebuild the lost concrete in the trough and along the lip with a cold-applied repair mortar, returning the section to profile.
4. Reprofile the weir lipWe reprofile the lip to a true, even edge so the water spreads evenly across the weir.
5. Line and return to serviceWe line the wetted launder with a smooth coating against the water and hand the trough back ready to carry an even overflow.