When it comes to repairing cracks in basement walls, there is no one-size-fits-all solution. Depending on the type of crack, the severity of the damage, and the desired outcome, different materials may be used. Two of the most popular materials for crack injection are epoxy and polyurethane. Epoxy has a more plastic texture and forms a hard bond once cured.
Epoxy injection is typically done on dry substrates, while polyurethane injection works well on wet and actively leaking substrates. Epoxy injection is the preferred method when structural crack repair is desired. The tensile strength of epoxy far exceeds that of the surrounding concrete base once cured. 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 and will stand the test of time without being worn out by water or the elements. The only downside to using epoxy is that it requires a trained technician to install it. This material does not come in do-it-yourself kits sold in box stores.
Proper training is required to properly install epoxy, but it is by far the strongest material for injecting into a concrete crack. For crack repair, a low viscosity injection resin specifically designed for structural crack repairs is typically used. This method requires 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. 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 polyurethanes are used, is gradual introduction of liquid polymer into the crack at low pressures (20 to 40 psi). Surface or low-pressure port injections involve 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 clay product can get through the cracks in wall, so it is definitely not recommended with finished basement. It could be changing earth that causes house to move or settle, pockets of rock on wall that over time allow water to enter basement or contractions from curing of concrete. When it comes to cracks in basement walls, repairing them requires careful consideration of all factors involved.