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What is a Waterstop?

Jeremy Laukkonen
Jeremy Laukkonen

A waterstop is a component that can be used to waterproof a concrete structure. The joints that exist where sections of concrete meet can present an opportunity for water to leak, so a number of methods have been developed to deal with this issue. Two two main types of waterstops are hydrophilic and hydrophobic, which are materials that either attract or repel water. The type of waterstop used in any given application depends on factors such as the type of structure and whether any initial leaking will be permissible. Some materials commonly used to construct waterstops include plastics such as polyvinyl chloride (PVC), metals such as copper or steel, and various natural or synthetic rubbers.

Most concrete is fairly waterproof, so it is often used in structures that need to withstand hydrostatic pressure. The weak point in any concrete structure is the joints where sections are connected, so this is where waterstops are required. A waterstop typically consists of some type of material that is placed between sections of concrete to effectively seal them together. Hydrophobic waterstops are designed to prevent water from entering the joints, while hydrophilic materials actually attract water, swell up, and tightly plug the joint. Each of these methods of plugging concrete joints are well suited to different applications.

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Man with a drill

Common hydrophobic waterstops include PVC, thermoplastic vulcanizate rubber (TPV), and various metals. These waterstops are best suited to applications where the concrete structure must be sealed up immediately and no initial leaking is permissible. Materials such as PVC and metals are typically used if there will be any movement of the joint. Hydrophobic rubbers may also be used in applications where the joint may move, since they can typically withstand both shear movements and hydrostatic pressure well. A secondary purpose of many waterstops is to provide a limited ability for the different concrete slabs to move in relationship to each other.

Hydrophilic waterstops are usually made of rubber that has been treated with chemicals such as bentonite. This type of waterstop is inserted into concrete joints, but does not provide any waterproofing ability until moisture is actually present. A hydrophilic waterstop will absorb water and swell up until it fills and plugs the joint it was inserted in. This can allow some amount of leakage until the waterstop has reached its final size. Hydrophilic waterstops can provide excellent resistance to hydrostatic pressure, though they typically do not withstand shear movement very well.

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