Epoxy has a more plastic texture and forms a hard bond once cured. Once cured, the tensile strength far exceeds that of the surrounding concrete base. Epoxy injection is typically done on dry substrates versus polyurethane injection which works very well on wet and actively leaking substrates. Epoxy injection is the preferred method when structural crack repair is desired.
Polyurethane foam also fills the crack or joint with a resin that expands in the presence of moisture. Unlike epoxy, polyurethane foam is flexible enough to adapt to movement in the crack or joint due to changing ground pressures or minor settling. Non-expandable epoxy adheres better to concrete. This resin will stand the test of time and will not be worn out by water or the elements.
The only downside to using Epoxy is that you need a trained and trained technician to install it. This material does not come in the do-it-yourself kits that are sold in box stores. Again, proper training is required to properly install, but this is by far the strongest material to inject into a concrete crack. For crack repair, a low viscosity injection resin specifically designed for structural crack repairs is typically used.
This method requires a little patience, but it allows the applicator to control the injection process and ensure that the crack is completely filled. Like epoxy, injected polyurethane fills the crack through the entire thickness of the foundation wall (typically 8”), thus preventing water from entering the crack. These types of cracks are usually smaller, and polyurethane is better suited to concrete that has shifted slightly. Most homeowners better identify concrete cracks in their basement, either in the foundation wall or in the floor.
Epoxy resins usually take several hours to harden after injection, which is ideal when it comes to filling large holes with many different cracks. Epoxy crack injections are typically performed at lower injection pressures (20-200 psi) and with surface mounted ports. The secret to effective injection of cracks, whether epoxies or polyurethane foams are used, is the gradual introduction of the liquid polymer into the crack at low pressures (20 to 40 psi). Surface or low-pressure port injections involve the use of surface-mounted injection ports to insert polyurethane into cracks.
In fact, because polyurethane resin systems are reactive to moisture, they may actually require that the crack be pre-wetted with a small amount of water to trigger full expansion of the resin. Epoxy resins formulated for use in structural and load-bearing applications are classified and specified in accordance with ASTM C-881 specifications for type, grade, and class. Polyurethane injections can be done by low-pressure or “surface port” (about 20-40 psi) or high-pressure injections (usually between 1500 and 3200 psi). The problem with this is that the repair is not instantaneous (it may take some rains to completely seal) and the clay product can get through the cracks in the wall, so it is definitely not recommended with a finished basement.
It could be the changing earth that causes the house to move or settle, the pockets of rock on the wall that, over time, allow water to enter the basement or the contractions from the curing of concrete. When it comes to cracks in basement walls, repairing them is not just a one-size-fits-all solution.