The Role of Waterstops in Waterproofing

About this course.

A waterstop is a purpose-made barrier placed within or across a joint in concrete to stop water passing through that joint. The short answer to what it does is that it creates a continuous seal along the line of the joint, so that even though the concrete on either side was cast at different times or is designed to move, water cannot travel through the gap between them. It is, in essence, a deliberate obstacle built into the weakest part of a concrete structure to force water to stay on one side.

To understand why this is necessary, picture how a large concrete structure is actually built. Concrete cannot usually be placed in one continuous pour; a basement wall, a tank, a retaining structure or a slab is cast in sections, and each place where fresh concrete meets already-hardened concrete is a construction joint. Even with good practice, the bond across such a joint is never as watertight as solid concrete, and a fine path can exist for water to seep through. Separately, structures are often designed to move — to expand and contract with temperature, to accommodate settlement or shrinkage — and this movement is managed by deliberate movement or expansion joints, which are intended gaps that must be allowed to open and close. Both kinds of joint are, by their nature, discontinuities in what we would otherwise want to be a continuous watertight envelope. The waterstop is the component that restores continuity of the water barrier across that discontinuity.