How to Seal Leaking Concrete Cracks with PU Foam Injection

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1 March 2022 - 16:42, by , in PU Injection, No comments

The choice of repair to resolve water bearing crack leaks was injection of polyurethane foam resin into concrete cracks. The damage was located under a lofted area with multiple windows and decorative shotcrete structures where gorillas were able to sit and be viewed by visitors.

Cracks were covered in efflorescence around the cold joints around the precast window frames as well as on the walls below the lofted area.

There were various degrees of water intrusion and leaks causing heavy efflorescence build-ups in cracks ranging from hairline to 1/4″ in joint seams. During snow melt and heavy rains, the roof and lofted area capture and feed water.

Singapore Waterproofing provided an on-site technical representative to consult with the contractor on injection methods using NSF/ANSI 61 Drinking Water Contact Certified injection grout,  a high-pressure injection pump and mechanical injection packers.

The Crack Injection Procedure Explained


Repair Method

A wire brush was used to remove efflorescence and dirt build up from the crack face before injection.

Once the cracks were visible, an injection plan was developed to fix the leaks from the lowest point upward.

Singapore Waterproofing uses its high pressure injection system – hydro-active, hydrophobic polyurethane foam resin, injection packers, and polyurethane crack injection pump – to create an airtight seal and to displace water from cracks.

Crack Injection Details



The Complex Injection Procedure

The placement of injection packers had to be modified in some areas due to more complex leaks and cold joints.

A spider-web crack pattern had developed as a result of multiple cracks connecting to an initial crack. We modified the injection procedure from the standard alternating “zipper” pattern typically recommended because of the complexity of the crack system and intersections of cracks. Because cracks were so close, packers needed to be strategically positioned in order to enhance the chance of each drill hole intersecting the crack – resulting in a less orderly placement pattern.

Starting at the low point of crack, the Water Stop Foam was injected till and foam travel was observed at a distance from the point of injection intersecting into other cracks. This meant that multiple cracks could be addressed from one point of injection without the need for drilling too many injection port holes.

Injection of the specific crack would be halted as the resin moved up and out of the crack, allowing the resin to expand fully and seal the crack.

Following the first injection, a second injection of the same packer was performed to penetrate even deeper into the crack and allow for visible vertical travel of foam resin.


After the cracks were successfully injected, the injection ports were removed, and a hydraulic cement patch was used to patch the ½” dill holes.


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