JOINTS AND WATERSTOPS

November 16, 2022
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In addition to membranes, coatings, and drainage, large commercial structures usually require some type of waterstop to keep groundwater from seeping into the building through joints and seams in the concrete.

These are available in a wide variety of shapes, sizes, and materials in order to meet the requirements of the different types of joints, amount of expected movement, hydrostatic pressure and chemical exposure.

SELECTING A WATERSTOP
For non-moving joints, such as the cold joint between a footing and foundation, expanding waterstops may be a good choice. Many products in this category use bentonite clay as the active component, but others use some other compound that is more forgiving of saltwater, chemicals, repeated wet/dry cycles and so on.

Regardless of the precise form-ulation, 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 is usually a matter of fastening the strip in or along the joint. Again, because this seal is easily broken, hydrophilic waterstops are suitable for non-moving joints only.

Crystalline products are also sometimes used to waterproof non-moving cold joints. Moving joints require mechanical waterstops, the type that spans both sides of the joint to create a diaphragm. Neoprene, PVC, and rubber are commonly used materials. These are ribbed, or have a thicker “dumbbell” of material on the ends to keep them in place and ensure maximum water-sealing performance. Profiles with a “bubble” in the middle of the strip are best for joints with lots of movement. In new construction, one side of the stop is embedded in the concrete during the first pour. The other half of the waterstop is encased in concrete when the other side of the joint is poured. Obviously, keeping the waterstop in place, with no folding or movement, requires considerable attention to detail. Usually it is fastened to the vertical rebar or form ties to keep it in place.

In the past decade, waterstops with integral injectable grout hoses have been developed, which allow joints to be sealed if leaks develop after construction is completed.

Regardless of the type installed, workers must ensure good consolidation around the waterstop. Those placed horizontally in slabs require particular attention, as it’s difficult to get concrete to flow into the gap between the bottom of the stop and the top of the forming bed.

T-shaped waterstops are available as a retrofit option. The flat side of the waterstop is secured to the existing concrete using epoxy or other specified adhesive, after which the new concrete is placed.

Read more: JOINTS AND WATERSTOPS

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