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Injection Connection – Using Urethane Injection Grout to Save the Foundation of a Historic Building

When the construction of a new condominium had compromised the structural integrity and waterproof qualities of the neighboring 120-year-old foundation wall, Scott Henson Architect was contacted to assist and monitor the experts repairing it to stabilize and prevent further damage.

It was determined that, over time, cracks had developed throughout the foundation walls of the building leading to water infiltration damage, mineral deposits, and staining. Contractors had previously installed a cast-in-place reinforced concrete matt bolted to the historic rubble foundation wall to provide structural reinforcing. Then they utilized a urethane injection grout system to repair the cracks and improve the foundation water proofing.

This system utilized urethane grout injected throughout the foundation of the building to improve its water proofing integrity. The process of installing urethane grout requires only the one-part grout, pumps for injection, and water to activate the urethane grout. The inexpensive nature, relatively simple installation, and the long-lasting results of urethane grout often makes this method ideal for underground foundation repair, even in older buildings.

Before beginning the process of injecting the grout, the contractor prepared the foundation wall by drilling a number of 5/8” – 3/4” diameter holes in the affected foundation wall in a grid, about 1 ½ to 2 feet apart. Next, expanding injection ports were installed in approximately half of the holes to allow for grout injection. The holes with no ports allowed for the team to observe spread and expansion of the urethane grout and spillage of extraneous water.

The urethane grout uses water as a catalyst to foam and expand to fill cavities. When the polyurethane reacts with water, rapid expansion throughout the structure will begin. We observed the contractor priming each port with water before injecting the grout material.

Using pumps, urethane grout was injected into each port at a pressure of 500-1,500 PSI. The contractor added water periodically to the foundation cavity to activate the urethane grout as it was injected. They were extremely careful to apply appropriate pressure to deliver grout throughout the cavity but not too much which could damage the rubble wall.

This process was repeated two to three times at each port to completely fill the foundation cavities and improve its integrity. The grout can expand to more than 15 times its original capacity when it reacts with water. Because only half of the holes are injected with the grout, it has room to spread throughout the cracks and imperfections in the foundation. As the grout activates and expands, it traveled up to 6 feet without spilling from the open holes. The grout also adheres to the concrete foundation as it expands and moves through the cavities.

Once all cracks were sealed and grout has cured, excess grout that leaked from gaps and holes can be removed for aesthetic purposes. At this point, if the work was thorough and carefully done, the grout should be strong enough to prevent water infiltration staining inside the foundation.

This method of urethane injection can be used for foundation wall repairs, or in this case, waterproofing. Once activated and cured, urethane grout improved the foundation of the building not only by sealing cracks and holes to prevent water infiltration, but also adding strength to the building foundation. Even buildings over a century old can maintain structural integrity and withstand many more years of use as new construction rises around it.

Scott Henson Architect was proud to be a part of preserving and restoring this historic building for the community. If you have damage to an older or historic building, reach out to us today for a consultation. We are proud to lend our expertise in both traditional and modern building preservation techniques, approaching each case with a creative emphasis on sustainability as well as an awareness of each building’s unique and storied past.