With waterstop, two is often better than one. If your concrete joint has the appropriate clearance, why not use one waterstop as your primary barrier and another as a secondary barrier as a kind of insurance policy? If the first system fails in any way due to manufacture or installation, the second system is there to ensure fluid-tight integrity at the concrete joint.
Because waterstop systems are relatively low cost, having a secondary product installed can be a wise and inexpensive investment.
Let me be clear, if a hydrophobic waterstop is properly installed, there really is no need for a secondary waterstop system. Regardless of polymer or manufacturer, these waterstop products really only leak from poor installation procedures and a lack of quality assurance. In my over 20 years in this industry, I am yet to see a waterstop burst or fail due to high hydrostatic water pressure. However, I often see improperly installed product that will result in failure and leakage.
A typical “belt and suspenders” approach would be to have an embedded hydrophobic on the high-pressure side of the joint and a hydrophilic or mastic strip-applied waterstop several inches away from it on the low pressure side. An alternative secondary waterstop would be an injection tube system placed on the low pressure side.
Another great option would be to utilize JPEB375 Integrated Capseal as the “belt” and JP211 Base Seal as the suspenders.
The benefits of redundancy in installed waterstop systems is great and the cost is low, especially when amortized over the extended life of the concrete structure they are installed in.