Concrete: The Universal Medium
Concrete is the universal medium. It is used more than any other artificial material in the world. In fact, the only naturally occurring material used more than concrete is water.
It is the perfect medium for water-retaining and water-excluding structures such as dams, viaducts, swimming pools, and basements.
However, a concrete structure is only as watertight as its construction or expansion joints. This is where concrete waterstops come in.
Your Guide to Concrete Waterstops
As the name suggests, a waterstop acts to stop water. It is typically a centrally placed seal between joints within concrete to prevent water from passing through.
Depending on the type of joint, different types of waterstops may be required, such as PVC or swellable waterstops.
What is the difference between a PVC and a swellable waterstop?
The main difference lies in their installation. PVC waterstops are generally cast 50% into the first concrete pour, with the remaining 50% cast into the second pour. This creates a physical barrier within the joint. The waterstop is effectively locked into both pours, preventing water from passing through in either direction.
Swellable waterstops, on the other hand, are typically adhered to the face of the first pour once the concrete has set. The waterstop then begins to swell when it comes into contact with water from the second pour. It can expand by over 200%, thereby creating a pressure seal.
About PVC Waterstops
There are a number of different types of PVC waterstops designed for various applications; however, they are typically joined at intersections by welding.
The ends of the joint are cut square or to the desired angle and fitted into a welding jig specific to the type of waterstop being welded. The ends are then heated to melting point using a welding iron. Once molten, they are brought together to fuse and form a continuous waterstop.
Hydrostop
Hydrostop is used as a waterstop between two new concrete structures. The two main types are centrally placed and externally placed. In short, the centrally placed (or centre stop) is placed in the center of the pour.
Generally speaking, the width of the waterstop is determined by the thickness of the concrete. For example, a 250mm thick slab requires a 250mm waterstop. However, this will usually be specified by an engineer.
The externally placed waterstop (or rearguard waterstop) is placed at the back of the joint between the two pours. This is typically adhered to the formwork.
Within these two types, there are two further common variations: waterstops for expansion joints or construction joints. The expansion joint waterstop features a "centre bulb" which allows for expansion and contraction of the joint, whereas the construction joint has no bulb.
