How to Seal Leaking Concrete Cracks with PU Foam Injection

Concrete crack injection with polyurethane foam resin was the choice of repair to resolve water bearing crack leaks. Crack related damages were located at a walkway under a lofted area with multiple windows and decorative shotcrete structures where gorillas could sit and be viewed by people walking through the exhibit.

The cracks were covered in efflorescence could be seen on the walls below the lofted area as well as cracks coming off the cold joints around the precast window framing.

The crack dimensions ranged from hairline to 1/4″ joint seams with varying degrees of water intrusion and active leaks causing heavy efflorescence build up. The roof and lofted area collect and feed water during snow melt and heavy rains.


The Crack Injection Procedure Explained

Repair Method

Prior to injection, the contractor had to first prep the cracks by removing any efflorescence and dirt build-up from the face of the crack using a wire brush.

Once the cracks were visible an injection plan was established to address the leaks working from the low point up.

Using the high pressure injection system — hydro-active, hydrophobic polyurethane foam resin, injection packers and polyurethane crack injection pump — hydro-active foam resin is injected into the cracks, expanding on contact with moisture and displacing any water in the process while creating an airtight & watertight seal.

Crack Injection Details

The Standard Injection Procedure

One side of the lofted area had three significant cracks that resulted in substantial active leaks.  The east wall presented larger actively leaking cracks. Further, cracks and cold joints from a precast window frame created an area of leakage that needed to be injected.

Starting with the lowest point of the cracks,  Leak Sealing Foam Grout was injected until positive refusal was observed on the interior and exterior of the wall. Due to the temperature of the wall, around 36 degrees Fahrenheit, the contractor was advised to condition the resin to room temperature prior to use as well as adding 15% of  Accelerator/Catalyst to compensate for the cooler ambient and substrate temperature — cold temperatures slow down the chemical reaction of the injection grout.

The Complex Injection Procedure

The placement of injection packers had to be modified in some cases to seal complex cracks and joints that leaked.

A spider-web crack pattern developed when multiple cracks connected to a larger crack. As a result of the complicated crack system and intersections of cracks, the injection procedure was modified from the standard alternating “zipper” pattern typically prescribed. The cracks were so close together that packers had to be placed strategically to increase the chance that each packer drill hole intersected the crack, resulting in a less orderly packer placement pattern.

Foam travel was observed at a distance from the point of injection intersecting other cracks after injecting Water Stop Foam at the low point of crack. Thus, multiple cracks could be injected simultaneously without needing to drill a large number of injection ports.

Injection of that specific crack would be stopped as the resin moves upward and out of the crack face, allowing the resin to fully expand and create a seal.

Afterwards, a second injection of the same packer was performed to penetrate even further into the crack and enable visible vertical foam resin travel to continue.


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