Waterstops & Joint Sealing Systems

Which waterstop for which joint

Cast-in PVC and rubber waterstops handle movement joints, where the joint is expected to open and close. Centrally placed profiles sit within the section; externally placed profiles sit on the outside face. The profile, including bulb arrangement and flange width, is selected for the expected movement and the hydrostatic head.

Hydrophilic strips swell on contact with water to seal construction joints, where the joint is not expected to move. They are fixed to the prepared joint face before the next pour and are simple to install, but they must be protected from rain and standing water before the pour, because premature swelling consumes the expansion capacity.

Injectable hose systems are cast into construction joints and allow resin injection later, either as planned practice or as a remedial fallback if the joint leaks. They give a second chance on critical joints where access after construction would be difficult.

Installation failures that cause leaks

Displacement during the pour is the most common problem. A waterstop that folds over, floats or is pushed aside no longer forms a barrier, and the defect is invisible once the concrete is placed. Fix the waterstop securely using the eyelets or purpose-made supports, and check it immediately before and during the pour.

Splices and junctions are the second common failure. PVC waterstops must be heat-welded with the correct jig, not overlapped, taped or glued. Factory-made junction pieces for tees, crosses and corners are more reliable than site-fabricated ones. Finally, compaction around the waterstop matters: honeycombing beside the flange creates the exact water path the waterstop was meant to prevent.

• •Fix securely so the waterstop cannot displace during the pour
• •Heat-weld splices with the correct jig, never overlap or tape
• •Use factory junction pieces for tees, crosses and corners
• •Compact carefully around the flange to avoid honeycombing
• •Keep hydrophilic strips dry until the pour
• •Maintain the specified concrete cover to the waterstop

Water-retaining structures

AS 3735 covers concrete structures retaining liquids and sets the design framework for crack control and joint design in tanks and reservoirs. Waterstop selection follows the joint design in that context rather than being chosen independently.

Where the retained liquid is drinking water, products in contact with it need to be suitable for potable water use, which is where AS/NZS 4020 testing is relevant. Confirm the grade for the specific product rather than assuming it applies to a whole range.