Waterstops play a crucial role in concrete construction, preventing seepage of water or other liquids through construction, contraction, and expansion joints. Some waterstops, made from materials such as polyvinyl chloride or rubber, are installed during the first concrete pour, generally requiring users to split formwork, tie the waterstop to reinforcing steel, or use special fabrications to go around corners. Other waterstops, supplied in preformed strips, are placed after the first concrete pour, easing the installation process. These strips of various materials and sizes are simple to install, but it's almost impossible for contractors to determine and correct problems after the second concrete placement. Therefore, it's critical that even strip-applied waterstops be selected and installed with care.
Choosing the proper strip-applied waterstop requires answers to at least two key questions: Can the waterstop withstand exposure to aggressive liquids without degrading? And, can the waterstop accommodate the expected joint movement?
Concrete surface preparation and waterstop installation procedures vary slightly depending on the type of product used. Products made with hydrophillic (water-loving) materials absorb water and swell to seal the joint--also filling honeycombed areas or cracks within the concrete. Products made with hydrophobic (water-repelling) materials are applied with an adhesive that creates a continuous chemical bond between the waterstop and the concrete.
Strip-applied waterstops are made from a wide variety of materials: bituminous strips; bentonite-based strips; hydrophillic rubber strips; and hydrophillic vinylester gaskets.