Construction joints and joints

Why a joint leaks

No real continuity forms between hardened concrete and fresh concrete: what is left is an interface with limited adhesion, often with a build-up of laitance and imperfect compaction. It is the preferred path for water in every below-grade structure, and the most frequent cause of leaks in tanks and basements.

The available technologies

Crystalline waterstop sheets. Galvanised steel strips coated on both sides, which lengthen the water's path, bond with the pour through their cementitious coating and seal cracks up to 0.4 mm thanks to the active crystalline coating.

Water-swellable joints. Profiles of sodium bentonite and butyl rubber, confined between the two pours: on contact with water they gradually increase in volume and seal by compression. They require adequate cover to confine the swelling.

Water-swellable polyurethane sealants. In cartridge form, extrudable with a gun: they solve irregular geometries, holes, cavities and points where a rigid profile does not fit.

Injection tubes. Embedded in the joint, they allow resin to be injected after the pour, either once a leak has occurred or as a preventive safeguard.

Formwork spacer holes

Every formwork spacer tube leaves a through-hole across the full thickness of the wall. On a below-grade wall there can be dozens of such deliberate perforations. They are closed with water-swellable rubber caps with a rigid core, tested against negative pressure, and protected on the outside with water-swellable annular gaskets.