Literally dozens of different waterstop designs are currently on the market, made from a wide range of materials. However, they can be grouped into two categories, depending on whether the joint is expected to move.

Non-Moving Joints: For non-moving joints, such as the cold-joint between a footing and foundation, hydrophilic waterstops may be a good choice. Most products in this category used expanding Bentonite clay as the active component. The others use materials with similar properties. Hydrotite, for instance, uses a non-Bentonite, modified chloroprene rubber, and Duro-Seal uses an acrylate polymer.

The architectural data sheet for PolyStop, another brand of hydrophilic waterstops, notes that, thanks to its non-Bentonite formula, “controlled swelling cuts risk of concrete spalling and reduces the possibility of premature expansion.”

In any case, all of these products work on a similar principle: Exposure to water makes the material expand dramatically, enough to create a compression seal and stop water from penetrating the joint.

Application technique is usually a simple matter of fastening the rubber strips in or along the joint. Again, because this seal is easily broken, hydrophilic waterstops are suitable for non-moving joints only.

There are few other products on the market designed to seal non-moving joints, although they’re not technically waterstops.

Mastic “waterstops” are basically a joint-sealing flashing. They’re applied with a primer adhesive along the joint to create a self-sealing moisture barrier.

Crystalline products are also sometimes used to waterproof non-moving cold joints. They’re roller- or spray-applied between pours. In the presence of water, the material produces millions of microscopic crystals which grow large enough to seal the joint.

Finally, Fuko Injection Waterstops are installed like a crack-injection or grouting operation, in which super-fine cement or epoxy resin is injected into the joint to seal all cracks and voids in the area. Once again, it’s not a traditional waterstop, but it does seal non-moving joints very effectively.

Joints With Movement: Moving joints require mechanical waterstops, the type that spans both sides of the joint to create a diaphragm. When designers and specifiers are speaking about waterstops, they’re usually referring to mechanical waterstops.

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